Jim Tcl(n)

# Jim Tcl(n) Manual Page

## NAME

Jim Tcl v0.79 - reference manual for the Jim Tcl scripting language

## SYNOPSIS

    cc <source> -ljim

or

    jimsh [<scriptfile>|-]
    jimsh -e '<immediate-script>'
    jimsh --version
    jimsh --help

Quick Index

- Command Reference

- Operator Precedence

- Builtin Variables

- Backslash Sequences

## INTRODUCTION

Jim Tcl is a small footprint reimplementation of the Tcl scripting language. The core language engine is compatible with Tcl 8.5+, while implementing a significant subset of the Tcl 8.6 command set, plus additional features available only in Jim Tcl.

Some notable differences with Tcl 8.5/8.6 are:

1. Object-based I/O (aio), but with a Tcl-compatibility layer

2. I/O: Support for sockets and pipes including udp, unix domain sockets and IPv6

3. Integers are 64bit

4. Support for references (`ref`/`getref`/`setref`) and garbage collection

5. Builtin dictionary type (`dict`) with some limitations compared to Tcl 8.6

6. `env` command to access environment variables

7. Operating system features: `os.fork`, `os.uptime`, `wait`, `signal`, `alarm`, `sleep`

8. Much better error reporting. `info` `stacktrace` as a replacement for $errorInfo, $errorCode

9. Support for "static" variables in procedures

10. Threads and coroutines are not supported

11. Command and variable traces are not supported

12. Built-in command line editing

13. Expression shorthand syntax: `$(…)`

14. Modular build allows many features to be omitted or built as dynamic, loadable modules

15. Highly suitable for use in an embedded environment

16. Support for UDP, IPv6, Unix-Domain sockets in addition to TCP sockets

## RECENT CHANGES

### Changes between 0.78 and 0.79

1. Add `file` `mtimeus` for high resolution file timestamps

2. `aio` now supports datagram Unix-Domain sockets

3. Add support for `aio` `lock -wait`

4. Add `signal` `block` to prevent delivery of signals

5. Add support for `file` `split`

6. Add support for `json::encode` and `json::decode`

7. `aio` `tty` now allows setting `echo` without full `raw` mode

### Changes between 0.77 and 0.78

1. Add serial/tty support with `aio` `tty`

2. Add support for jimsh -

3. Add hidden -commands option to many commands

4. Add scriptable autocompletion support in interactive mode with `tcl::autocomplete`

5. Add `aio` `sockopt`

6. Add scriptable autocompletion support with `history` `completion`

7. Add support for `tree` `delete`

8. Add support for `defer` and $jim::defer

9. Renamed `os.wait` to `wait`, now more Tcl-compatible and compatible with `exec` `... &`

10. `pipe` is now a synonym for `socket` `pipe`

11. Closing a pipe open with `open` `|...` now returns Tcl-like status

12. It is now possible to used `exec` redirection with a pipe opened with `open` `|...`

13. Interactive line editing now supports multiline mode if $::history::multiline is set

### Changes between 0.76 and 0.77

1. Add support for `aio` `sync`

2. Add SSL and TLS support in aio

3. Added `zlib`

4. Added support for boolean constants in `expr`

5. `string` `is` now supports boolean class

6. Add support for `aio` `lock` and `aio` `unlock`

7. Add new `interp` command

### Changes between 0.75 and 0.76

1. `glob` now supports the `-tails` option

2. Add support for `string` `cat`

3. Allow `info` `source` to add source info

### Changes between 0.74 and 0.75

1. `binary`, `pack` and `unpack` now support floating point

2. `file` `copy` `-force` handles source and target as the same file

3. `format` now supports `%b` for binary conversion

4. `lsort` now supports `-unique` and `-real`

5. Add support for half-close with `aio` `close` `?r|w?`

6. Add `socket` `pair` for a bidirectional pipe

7. Add --random-hash to randomise hash tables for greater security

8. `dict` now supports for, values, incr, append, lappend, update, info and replace

9. `file` `stat` no longer requires the variable name

10. Add support for `file` `link`

## TCL INTRODUCTION

Tcl stands for tool command language and is pronounced tickle. It is actually two things: a language and a library.

First, Tcl is a simple textual language, intended primarily for issuing commands to interactive programs such as text editors, debuggers, illustrators, and shells. It has a simple syntax and is also programmable, so Tcl users can write command procedures to provide more powerful commands than those in the built-in set.

Second, Tcl is a library package that can be embedded in application programs. The Tcl library consists of a parser for the Tcl language, routines to implement the Tcl built-in commands, and procedures that allow each application to extend Tcl with additional commands specific to that application. The application program generates Tcl commands and passes them to the Tcl parser for execution. Commands may be generated by reading characters from an input source, or by associating command strings with elements of the application’s user interface, such as menu entries, buttons, or keystrokes.

When the Tcl library receives commands it parses them into component fields and executes built-in commands directly. For commands implemented by the application, Tcl calls back to the application to execute the commands. In many cases commands will invoke recursive invocations of the Tcl interpreter by passing in additional strings to execute (procedures, looping commands, and conditional commands all work in this way).

An application program gains three advantages by using Tcl for its command language. First, Tcl provides a standard syntax: once users know Tcl, they will be able to issue commands easily to any Tcl-based application. Second, Tcl provides programmability. All a Tcl application needs to do is to implement a few application-specific low-level commands. Tcl provides many utility commands plus a general programming interface for building up complex command procedures. By using Tcl, applications need not re-implement these features.

Third, Tcl can be used as a common language for communicating between applications. Inter-application communication is not built into the Tcl core described here, but various add-on libraries, such as the Tk toolkit, allow applications to issue commands to each other. This makes it possible for applications to work together in much more powerful ways than was previously possible.

Fourth, Jim Tcl includes a command processor, `jimsh`, which can be used to run standalone Tcl scripts, or to run Tcl commands interactively.

This manual page focuses primarily on the Tcl language. It describes the language syntax and the built-in commands that will be available in any application based on Tcl. The individual library procedures are described in more detail in separate manual pages, one per procedure.

## JIMSH COMMAND INTERPRETER

A simple, but powerful command processor, `jimsh`, is part of Jim Tcl. It may be invoked in interactive mode as:

    jimsh

or to process the Tcl script in a file with:

    jimsh filename

or to process the Tcl script from standard input:

    jimsh -

It may also be invoked to execute an immediate script with:

    jimsh -e "script"

### Interactive Mode

Interactive mode reads Tcl commands from standard input, evaluates those commands and prints the results.

    $ jimsh
    Welcome to Jim version 0.73, Copyright (c) 2005-8 Salvatore Sanfilippo
    . info version
    0.73
    . lsort [info commands p*]
    package parray pid popen proc puts pwd
    . foreach i {a b c} {
    {> puts $i
    {> }
    a
    b
    c
    . bad
    invalid command name "bad"
    [error] . exit
    $

If `jimsh` is configured with line editing (it is by default) and a VT-100-compatible terminal is detected, Emacs-style line editing commands are available, including: arrow keys, `^W` to erase a word, `^U` to erase the line, `^R` for reverse incremental search in history. Additionally, the `h` command may be used to display the command history.

Command line history is automatically saved and loaded from `~/.jim_history`

In interactive mode, `jimsh` automatically runs the script `~/.jimrc` at startup if it exists.

## INTERPRETERS

The central data structure in Tcl is an interpreter (C type Jim_Interp). An interpreter consists of a set of command bindings, a set of variable values, and a few other miscellaneous pieces of state. Each Tcl command is interpreted in the context of a particular interpreter.

Some Tcl-based applications will maintain multiple interpreters simultaneously, each associated with a different widget or portion of the application. Interpreters are relatively lightweight structures. They can be created and deleted quickly, so application programmers should feel free to use multiple interpreters if that simplifies the application.

## DATA TYPES

Tcl supports only one type of data: strings. All commands, all arguments to commands, all command results, and all variable values are strings.

Where commands require numeric arguments or return numeric results, the arguments and results are passed as strings. Many commands expect their string arguments to have certain formats, but this interpretation is up to the individual commands. For example, arguments often contain Tcl command strings, which may get executed as part of the commands. The easiest way to understand the Tcl interpreter is to remember that everything is just an operation on a string. In many cases Tcl constructs will look similar to more structured constructs from other languages. However, the Tcl constructs are not structured at all; they are just strings of characters, and this gives them a different behaviour than the structures they may look like.

Although the exact interpretation of a Tcl string depends on who is doing the interpretation, there are three common forms that strings take: commands, expressions, and lists. The major sections below discuss these three forms in more detail.

## BASIC COMMAND SYNTAX

The Tcl language has syntactic similarities to both the Unix shells and Lisp. However, the interpretation of commands is different in Tcl than in either of those other two systems. A Tcl command string consists of one or more commands separated by newline characters or semi-colons. Each command consists of a collection of fields separated by white space (spaces or tabs). The first field must be the name of a command, and the additional fields, if any, are arguments that will be passed to that command. For example, the command:

        set a 22

has three fields: the first, `set`, is the name of a Tcl command, and the last two, a and 22, will be passed as arguments to the `set` command. The command name may refer either to a built-in Tcl command, an application-specific command bound in with the library procedure Jim_CreateCommand, or a command procedure defined with the `proc` built-in command.

Arguments are passed literally as text strings. Individual commands may interpret those strings in any fashion they wish. The `set` command, for example, will treat its first argument as the name of a variable and its second argument as a string value to assign to that variable. For other commands arguments may be interpreted as integers, lists, file names, or Tcl commands.

Command names should normally be typed completely (e.g. no abbreviations). However, if the Tcl interpreter cannot locate a command it invokes a special command named `unknown` which attempts to find or create the command.

For example, at many sites `unknown` will search through library directories for the desired command and create it as a Tcl procedure if it is found. The `unknown` command often provides automatic completion of abbreviated commands, but usually only for commands that were typed interactively.

It’s probably a bad idea to use abbreviations in command scripts and other forms that will be re-used over time: changes to the command set may cause abbreviations to become ambiguous, resulting in scripts that no longer work.

## COMMENTS

If the first non-blank character in a command is `#`, then everything from the `#` up through the next newline character is treated as a comment and ignored. When comments are embedded inside nested commands (e.g. fields enclosed in braces) they must have properly-matched braces (this is necessary because when Tcl parses the top-level command it doesn’t yet know that the nested field will be used as a command so it cannot process the nested comment character as a comment).

## GROUPING ARGUMENTS WITH DOUBLE-QUOTES

Normally each argument field ends at the next white space, but double-quotes may be used to create arguments with embedded space.

If an argument field begins with a double-quote, then the argument isn’t terminated by white space (including newlines) or a semi-colon (see below for information on semi-colons); instead it ends at the next double-quote character. The double-quotes are not included in the resulting argument. For example, the command

        set a "This is a single argument"

will pass two arguments to `set`: a and This is a single argument.

Within double-quotes, command substitutions, variable substitutions, and backslash substitutions still occur, as described below. If the first character of a command field is not a quote, then quotes receive no special interpretation in the parsing of that field.

## GROUPING ARGUMENTS WITH BRACES

Curly braces may also be used for grouping arguments. They are similar to quotes except for two differences. First, they nest; this makes them easier to use for complicated arguments like nested Tcl command strings. Second, the substitutions described below for commands, variables, and backslashes do not occur in arguments enclosed in braces, so braces can be used to prevent substitutions where they are undesirable.

If an argument field begins with a left brace, then the argument ends at the matching right brace. Tcl will strip off the outermost layer of braces and pass the information between the braces to the command without any further modification. For example, in the command

        set a {xyz a {b c d}}

the `set` command will receive two arguments: a and xyz a {b c d}.

When braces or quotes are in effect, the matching brace or quote need not be on the same line as the starting quote or brace; in this case the newline will be included in the argument field along with any other characters up to the matching brace or quote. For example, the `eval` command takes one argument, which is a command string; `eval` invokes the Tcl interpreter to execute the command string. The command

        eval {
          set a 22
          set b 33
        }

will assign the value 22 to a and 33 to b.

If the first character of a command field is not a left brace, then neither left nor right braces in the field will be treated specially (except as part of variable substitution; see below).

## COMMAND SUBSTITUTION WITH BRACKETS

If an open bracket occurs in a field of a command, then command substitution occurs (except for fields enclosed in braces). All of the text up to the matching close bracket is treated as a Tcl command and executed immediately. Then the result of that command is substituted for the bracketed text. For example, consider the command

        set a [set b]

When the `set` command has only a single argument, it is the name of a variable and `set` returns the contents of that variable. In this case, if variable b has the value foo, then the command above is equivalent to the command

        set a foo

Brackets can be used in more complex ways. For example, if the variable b has the value foo and the variable c has the value gorp, then the command

        set a xyz[set b].[set c]

is equivalent to the command

        set a xyzfoo.gorp

A bracketed command may contain multiple commands separated by newlines or semi-colons in the usual fashion. In this case the value of the last command is used for substitution. For example, the command

        set a x[set b 22
        expr $b+2]x

is equivalent to the command

        set a x24x

If a field is enclosed in braces then the brackets and the characters between them are not interpreted specially; they are passed through to the argument verbatim.

## VARIABLE SUBSTITUTION WITH $

The dollar sign (`$`) may be used as a special shorthand form for substituting variable values. If `$` appears in an argument that isn’t enclosed in braces then variable substitution will occur. The characters after the `$`, up to the first character that isn’t a number, letter, or underscore, are taken as a variable name and the string value of that variable is substituted for the name.

For example, if variable foo has the value test, then the command

        set a $foo.c

is equivalent to the command

        set a test.c

There are two special forms for variable substitution. If the next character after the name of the variable is an open parenthesis, then the variable is assumed to be an array name, and all of the characters between the open parenthesis and the next close parenthesis are taken as an index into the array. Command substitutions and variable substitutions are performed on the information between the parentheses before it is used as an index.

For example, if the variable x is an array with one element named first and value 87 and another element named 14 and value more, then the command

        set a xyz$x(first)zyx

is equivalent to the command

        set a xyz87zyx

If the variable index has the value 14, then the command

        set a xyz$x($index)zyx

is equivalent to the command

        set a xyzmorezyx

For more information on arrays, see VARIABLES - SCALARS AND ARRAYS below.

The second special form for variables occurs when the dollar sign is followed by an open curly brace. In this case the variable name consists of all the characters up to the next curly brace.

Array references are not possible in this form: the name between braces is assumed to refer to a scalar variable. For example, if variable foo has the value test, then the command

        set a abc${foo}bar

is equivalent to the command

        set a abctestbar

Variable substitution does not occur in arguments that are enclosed in braces: the dollar sign and variable name are passed through to the argument verbatim.

The dollar sign abbreviation is simply a shorthand form. `$a` is completely equivalent to `[set a]`; it is provided as a convenience to reduce typing.

## SEPARATING COMMANDS WITH SEMI-COLONS

Normally, each command occupies one line (the command is terminated by a newline character). However, semi-colon (`;`) is treated as a command separator character; multiple commands may be placed on one line by separating them with a semi-colon. Semi-colons are not treated as command separators if they appear within curly braces or double-quotes.

## BACKSLASH SUBSTITUTION

Backslashes may be used to insert non-printing characters into command fields and also to insert special characters like braces and brackets into fields without them being interpreted specially as described above.

The backslash sequences understood by the Tcl interpreter are listed below. In each case, the backslash sequence is replaced by the given character:

`\b`

  Backspace (0x8)

`\f`

  Form feed (0xc)

`\n`

  Newline (0xa)

`\r`

  Carriage-return (0xd).

`\t`

  Tab (0x9).

`\v`

  Vertical tab (0xb).

`\{`

  Left brace ({).

`\}`

  Right brace (}).

`\[`

  Open bracket ([).

`\]`

  Close bracket (]).

`\$`

  Dollar sign ($).

`\<space>`

  Space ( ): doesn’t terminate argument.

`\;`

  Semi-colon: doesn’t terminate command.

`\"`

  Double-quote.

`\<newline>`

  Nothing: this joins two lines together into a single line. This backslash feature is unique in that it will be applied even when the sequence occurs within braces.

`\\`

  Backslash (\).

`\ddd`

  The digits `ddd` (one, two, or three of them) give the octal value of the character. Note that Jim supports null characters in strings.

`\unnnn`
`\u{nnn}`
`\Unnnnnnnn`

  The UTF-8 encoding of the unicode codepoint represented by the hex digits, `nnnn`, is inserted. The u form allows for one to four hex digits. The U form allows for one to eight hex digits. The u{nnn} form allows for one to eight hex digits, but makes it easier to insert characters UTF-8 characters which are followed by a hex digit.

For example, in the command

        set a \{x\[\ yz\141

the second argument to `set` will be `{x[ yza`.

If a backslash is followed by something other than one of the options described above, then the backslash is transmitted to the argument field without any special processing, and the Tcl scanner continues normal processing with the next character. For example, in the command

        set \*a \\\{foo

The first argument to `set` will be `\*a` and the second argument will be `\{foo`.

If an argument is enclosed in braces, then backslash sequences inside the argument are parsed but no substitution occurs (except for backslash-newline): the backslash sequence is passed through to the argument as is, without making any special interpretation of the characters in the backslash sequence. In particular, backslashed braces are not counted in locating the matching right brace that terminates the argument. For example, in the command

        set a {\{abc}

the second argument to `set` will be `\{abc`.

This backslash mechanism is not sufficient to generate absolutely any argument structure; it only covers the most common cases. To produce particularly complicated arguments it is probably easiest to use the `format` command along with command substitution.

## STRING AND LIST INDEX SPECIFICATIONS

Many string and list commands take one or more index parameters which specify a position in the string relative to the start or end of the string/list.

The index may be one of the following forms:

`integer`

  A simple integer, where 0 refers to the first element of the string or list.

`integer+integer` or
`integer-integer`

  The sum or difference of the two integers. e.g. `2+3` refers to the 5th element. This is useful when used with (e.g.) `$i+1` rather than the more verbose `[expr {$i+1}]`

`end`

  The last element of the string or list.

`end-integer`

  The nth-from-last element of the string or list.

## COMMAND SUMMARY

1. A command is just a string.

2. Within a string commands are separated by newlines or semi-colons (unless the newline or semi-colon is within braces or brackets or is backslashed).

3. A command consists of fields. The first field is the name of the command. The other fields are strings that are passed to that command as arguments.

4. Fields are normally separated by white space.

5. Double-quotes allow white space and semi-colons to appear within a single argument. Command substitution, variable substitution, and backslash substitution still occur inside quotes.

6. Braces defer interpretation of special characters. If a field begins with a left brace, then it consists of everything between the left brace and the matching right brace. The braces themselves are not included in the argument. No further processing is done on the information between the braces except that backslash-newline sequences are eliminated.

7. If a field doesn’t begin with a brace then backslash, variable, and command substitution are done on the field. Only a single level of processing is done: the results of one substitution are not scanned again for further substitutions or any other special treatment. Substitution can occur on any field of a command, including the command name as well as the arguments.

8. If the first non-blank character of a command is a `#`, everything from the `#` up through the next newline is treated as a comment and ignored.

## EXPRESSIONS

The second major interpretation applied to strings in Tcl is as expressions. Several commands, such as `expr`, `for`, and `if`, treat one or more of their arguments as expressions and call the Tcl expression processors (Jim_ExprLong, Jim_ExprBoolean, etc.) to evaluate them.

The operators permitted in Tcl expressions are a subset of the operators permitted in C expressions, and they have the same meaning and precedence as the corresponding C operators. Expressions almost always yield numeric results (integer or floating-point values). For example, the expression

        8.2 + 6

evaluates to 14.2.

Tcl expressions differ from C expressions in the way that operands are specified, and in that Tcl expressions support non-numeric operands and string comparisons.

A Tcl expression consists of a combination of operands, operators, and parentheses.

White space may be used between the operands and operators and parentheses; it is ignored by the expression processor. Where possible, operands are interpreted as integer values.

Integer values may be specified in decimal (the normal case) or in hexadecimal (if the first two characters of the operand are 0x). Note that Jim Tcl does not treat numbers with leading zeros as octal.

If an operand does not have one of the integer formats given above, then it is treated as a floating-point number if that is possible. Floating-point numbers may be specified in any of the ways accepted by an ANSI-compliant C compiler (except that the f, F, l, and L suffixes will not be permitted in most installations). For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16.

If no numeric interpretation is possible, then an operand is left as a string (and only a limited set of operators may be applied to it).

String constants representing boolean constants (`0`, `1`, `false`, `off`, `no`, `true`, `on`, `yes`) are also recognized and can be used in logical operations.

1. Operands may be specified in any of the following ways:

2. As a numeric value, either integer or floating-point.

3. As one of valid boolean constants

4. As a Tcl variable, using standard $ notation. The variable’s value will be used as the operand.

5. As a string enclosed in double-quotes. The expression parser will perform backslash, variable, and command substitutions on the information between the quotes, and use the resulting value as the operand

6. As a string enclosed in braces. The characters between the open brace and matching close brace will be used as the operand without any substitutions.

7. As a Tcl command enclosed in brackets. The command will be executed and its result will be used as the operand.

Where substitutions occur above (e.g. inside quoted strings), they are performed by the expression processor. However, an additional layer of substitution may already have been performed by the command parser before the expression processor was called.

As discussed below, it is usually best to enclose expressions in braces to prevent the command parser from performing substitutions on the contents.

For some examples of simple expressions, suppose the variable a has the value 3 and the variable b has the value 6. Then the expression on the left side of each of the lines below will evaluate to the value on the right side of the line:

        $a + 3.1                6.1
        2 + "$a.$b"             5.6
        4*[llength "6 2"]       8
        {word one} < "word $a"  0

The valid operators are listed below, grouped in decreasing order of precedence:

`int() double() round() abs(), rand(), srand()`

  Unary functions (except rand() which takes no arguments)

  - `int()` converts the numeric argument to an integer by truncating down.

  - `double()` converts the numeric argument to floating point.

  - `round()` converts the numeric argument to the closest integer value.

  - `abs()` takes the absolute value of the numeric argument.

  - `rand()` returns a pseudo-random floating-point value in the range (0,1).

  - `srand()` takes an integer argument to (re)seed the random number generator. Returns the first random number from that seed.

`sin() cos() tan() asin() acos() atan() sinh() cosh() tanh() ceil() floor() exp() log() log10() sqrt()`

  Unary math functions. If Jim is compiled with math support, these functions are available.

`- + ~ !`

  Unary minus, unary plus, bit-wise NOT, logical NOT. None of these operands may be applied to string operands, and bit-wise NOT may be applied only to integers.

`** pow(x,y)`

  Power. e.g. xy. If Jim is compiled with math support, supports doubles and integers. Otherwise supports integers only. (Note that the math-function form has the same highest precedence)

`* / %`

  Multiply, divide, remainder. None of these operands may be applied to string operands, and remainder may be applied only to integers.

`+ -`

  Add and subtract. Valid for any numeric operands.

`<< >> <<< >>>`

  Left and right shift, left and right rotate. Valid for integer operands only.

`< > <= >=`

  Boolean less, greater, less than or equal, and greater than or equal. Each operator produces 1 if the condition is true, 0 otherwise. These operators may be applied to strings as well as numeric operands, in which case string comparison is used.

`== !=`

  Boolean equal and not equal. Each operator produces a zero/one result. Valid for all operand types. Note that values will be converted to integers if possible, then floating point types, and finally strings will be compared. It is recommended that eq and ne should be used for string comparison.

`eq ne`

  String equal and not equal. Uses the string value directly without attempting to convert to a number first.

`in ni`

  String in list and not in list. For in, result is 1 if the left operand (as a string) is contained in the right operand (as a list), or 0 otherwise. The result for `{$a ni $list}` is equivalent to `{!($a in $list)}`.

`&`

  Bit-wise AND. Valid for integer operands only.

`|`

  Bit-wise OR. Valid for integer operands only.

`^`

  Bit-wise exclusive OR. Valid for integer operands only.

`&&`

  Logical AND. Produces a 1 result if both operands are non-zero, 0 otherwise. Valid for numeric operands only (integers or floating-point).

`||`

  Logical OR. Produces a 0 result if both operands are zero, 1 otherwise. Valid for numeric operands only (integers or floating-point).

`x ? y : z`

  If-then-else, as in C. If `x` evaluates to non-zero, then the result is the value of `y`. Otherwise the result is the value of `z`. The `x` operand must have a numeric value, while `y` and `z` can be of any type.

See the C manual for more details on the results produced by each operator. All of the binary operators group left-to-right within the same precedence level. For example, the expression

        4*2 < 7

evaluates to 0.

The `&&`, `||`, and `?:` operators have lazy evaluation, just as in C, which means that operands are not evaluated if they are not needed to determine the outcome. For example, in

        $v ? [a] : [b]

only one of `[a]` or `[b]` will actually be evaluated, depending on the value of `$v`.

All internal computations involving integers are done with the C type long long if available, or long otherwise, and all internal computations involving floating-point are done with the C type double.

When converting a string to floating-point, exponent overflow is detected and results in a Tcl error. For conversion to integer from string, detection of overflow depends on the behaviour of some routines in the local C library, so it should be regarded as unreliable. In any case, overflow and underflow are generally not detected reliably for intermediate results.

Conversion among internal representations for integer, floating-point, string operands is done automatically as needed. For arithmetic computations, integers are used until some floating-point number is introduced, after which floating-point is used. For example,

        5 / 4

yields the result 1, while

        5 / 4.0
        5 / ( [string length "abcd"] + 0.0 )

both yield the result 1.25.

String values may be used as operands of the comparison operators, although the expression evaluator tries to do comparisons as integer or floating-point when it can. If one of the operands of a comparison is a string and the other has a numeric value, the numeric operand is converted back to a string using the C sprintf format specifier %d for integers and %g for floating-point values. For example, the expressions

        "0x03" > "2"
        "0y" < "0x12"

both evaluate to 1. The first comparison is done using integer comparison, and the second is done using string comparison after the second operand is converted to the string 18.

In general it is safest to enclose an expression in braces when entering it in a command: otherwise, if the expression contains any white space then the Tcl interpreter will split it among several arguments. For example, the command

        expr $a + $b

results in three arguments being passed to `expr`: `$a`, +, and `$b`. In addition, if the expression isn’t in braces then the Tcl interpreter will perform variable and command substitution immediately (it will happen in the command parser rather than in the expression parser). In many cases the expression is being passed to a command that will evaluate the expression later (or even many times if, for example, the expression is to be used to decide when to exit a loop). Usually the desired goal is to re-do the variable or command substitutions each time the expression is evaluated, rather than once and for all at the beginning. For example, the command

        for {set i 1} $i<=10 {incr i} {...}        ** WRONG **

is probably intended to iterate over all values of `i` from 1 to 10. After each iteration of the body of the loop, `for` will pass its second argument to the expression evaluator to see whether or not to continue processing. Unfortunately, in this case the value of `i` in the second argument will be substituted once and for all when the `for` command is parsed. If `i` was 0 before the `for` command was invoked then the second argument of `for` will be `0<=10` which will always evaluate to 1, even though `i` eventually becomes greater than 10. In the above case the loop will never terminate. Instead, the expression should be placed in braces:

        for {set i 1} {$i<=10} {incr i} {...}      ** RIGHT **

This causes the substitution of i to be delayed; it will be re-done each time the expression is evaluated, which is the desired result.

## LISTS

The third major way that strings are interpreted in Tcl is as lists. A list is just a string with a list-like structure consisting of fields separated by white space. For example, the string

        Al Sue Anne John

is a list with four elements or fields. Lists have the same basic structure as command strings, except that a newline character in a list is treated as a field separator just like space or tab. Conventions for braces and quotes and backslashes are the same for lists as for commands. For example, the string

        a b\ c {d e {f g h}}

is a list with three elements: `a`, `b c`, and `d e {f g h}`.

Whenever an element is extracted from a list, the same rules about braces and quotes and backslashes are applied as for commands. Thus in the example above when the third element is extracted from the list, the result is

        d e {f g h}

(when the field was extracted, all that happened was to strip off the outermost layer of braces). Command substitution and variable substitution are never made on a list (at least, not by the list-processing commands; the list can always be passed to the Tcl interpreter for evaluation).

The Tcl commands `concat`, `foreach`, `lappend`, `lindex`, `linsert`, `list`, `llength`, `lrange`, `lreplace`, `lsearch`, and `lsort` allow you to build lists, extract elements from them, search them, and perform other list-related functions.

Advanced list commands include `lrepeat`, `lreverse`, `lmap`, `lassign`, `lset`.

## LIST EXPANSION

A new addition to Tcl 8.5 is the ability to expand a list into separate arguments. Support for this feature is also available in Jim.

Consider the following attempt to exec a list:

        set cmd {ls -l}
        exec $cmd

This will attempt to exec a command named "ls -l", which will clearly not work. Typically eval and concat are required to solve this problem, however it can be solved much more easily with `{*}`.

        exec {*}$cmd

This will expand the following argument into individual elements and then evaluate the resulting command.

Note that the official Tcl syntax is `{*}`, however `{expand}` is retained for backward compatibility with experimental versions of this feature.

## REGULAR EXPRESSIONS

Tcl provides two commands that support string matching using regular expressions, `regexp` and `regsub`, as well as `switch` `-regexp` and `lsearch` `-regexp`.

Regular expressions may be implemented one of two ways. Either using the system’s C library POSIX regular expression support, or using the built-in regular expression engine. The differences between these are described below.

NOTE Tcl 7.x and 8.x use perl-style Advanced Regular Expressions (`ARE`).

### POSIX Regular Expressions

If the system supports POSIX regular expressions, and UTF-8 support is not enabled, this support will be used by default. The type of regular expressions supported are Extended Regular Expressions (`ERE`) rather than Basic Regular Expressions (`BRE`). See REG_EXTENDED in the documentation.

Using the system-supported POSIX regular expressions will typically make for the smallest code size, but some features such as UTF-8 and `\w`, `\d`, `\s` are not supported, and null characters in strings are not supported.

See regex(3) and regex(7) for full details.

### Jim built-in Regular Expressions

The Jim built-in regular expression engine may be selected with `./configure --with-jim-regexp` or it will be selected automatically if UTF-8 support is enabled.

This engine supports UTF-8 as well as some `ARE` features. The differences with both Tcl 7.x/8.x and POSIX are highlighted below.

1. UTF-8 strings and patterns are both supported

2. All Tcl character classes are supported (e.g. `[:alnum:]`, `[:digit:]`, `[:space:]`), but…

3. Character classes apply to ASCII characters only

4. Supported shorthand character classes: `\w` = `[:alnum:]`, `\W` = `[:alnum:]`, `\d` = `[:digit:],` `\D` = `[:digit:],` `\s` = `[:space:]`, + `\S` = `^[:space:]`

5. Supported constraint escapes: `\m` = `\<` = start of word, `\M` = `\>` = end of word

6. Backslash escapes may be used within regular expressions, such as `\n` = newline, `\uNNNN` = unicode

7. Partially supported constraint escapes: `\A` = start of string, `\Z` = end of string

8. Support for the `?` non-greedy quantifier. e.g. `*?`

9. Support for non-capturing parentheses `(?:…)`

10. Jim Tcl considers that both patterns and strings end at a null character (`\x00`)

## COMMAND RESULTS

Each command produces two results: a code and a string. The code indicates whether the command completed successfully or not, and the string gives additional information. The valid codes are defined in jim.h, and are:

`JIM_OK(0)`

  This is the normal return code, and indicates that the command completed successfully. The string gives the command’s return value.

`JIM_ERR(1)`

  Indicates that an error occurred; the string gives a message describing the error.

`JIM_RETURN(2)`

  Indicates that the `return` command has been invoked, and that the current procedure (or top-level command or `source` command) should return immediately. The string gives the return value for the procedure or command.

`JIM_BREAK(3)`

  Indicates that the `break` command has been invoked, so the innermost loop should abort immediately. The string should always be empty.

`JIM_CONTINUE(4)`

  Indicates that the `continue` command has been invoked, so the innermost loop should go on to the next iteration. The string should always be empty.

`JIM_SIGNAL(5)`

  Indicates that a signal was caught while executing a commands. The string contains the name of the signal caught. See the `signal` and `catch` commands.

`JIM_EXIT(6)`

  Indicates that the command called the `exit` command. The string contains the exit code.

Tcl programmers do not normally need to think about return codes, since `JIM_OK` is almost always returned. If anything else is returned by a command, then the Tcl interpreter immediately stops processing commands and returns to its caller. If there are several nested invocations of the Tcl interpreter in progress, then each nested command will usually return the error to its caller, until eventually the error is reported to the top-level application code. The application will then display the error message for the user.

In a few cases, some commands will handle certain `error` conditions themselves and not return them upwards. For example, the `for` command checks for the `JIM_BREAK` code; if it occurs, then `for` stops executing the body of the loop and returns `JIM_OK` to its caller. The `for` command also handles `JIM_CONTINUE` codes and the procedure interpreter handles `JIM_RETURN` codes. The `catch` command allows Tcl programs to catch errors and handle them without aborting command interpretation any further.

The `info` `returncodes` command may be used to programmatically map between return codes and names.

## PROCEDURES

Tcl allows you to extend the command interface by defining procedures. A Tcl procedure can be invoked just like any other Tcl command (it has a name and it receives one or more arguments). The only difference is that its body isn’t a piece of C code linked into the program; it is a string containing one or more other Tcl commands.

The `proc` command is used to create a new Tcl command procedure:

`proc name arglist ?statics? body`

The new command is named `name`, and it replaces any existing command there may have been by that name. Whenever the new command is invoked, the contents of `body` will be executed by the Tcl interpreter.

`arglist` specifies the formal arguments to the procedure. It consists of a list, possibly empty, of the following argument specifiers:

`name`

  Required Argument - A simple argument name.

`{name default}`

  Optional Argument - A two-element list consisting of the argument name, followed by the default value, which will be used if the corresponding argument is not supplied.

`&name`

  Reference Argument - The caller is expected to pass the name of an existing variable. An implicit ``upvar` 1 origname name` is done to make the variable available in the proc scope.

`args`

  Variable Argument - The special name `args`, which is assigned all remaining arguments (including none) as a list. The variable argument may only be specified once. Note that the syntax `{args newname}` may be used to retain the special behaviour of `args` with a different local name. In this case, the variable is named `newname` rather than `args`.

When the command is invoked, a local variable will be created for each of the formal arguments to the procedure; its value will be the value of corresponding argument in the invoking command or the argument’s default value.

Arguments with default values need not be specified in a procedure invocation. However, there must be enough actual arguments for all required arguments, and there must not be any extra actual arguments (unless the Variable Argument is specified).

Actual arguments are assigned to formal arguments as in left-to-right order with the following precedence.

1. Required Arguments (including Reference Arguments)

2. Optional Arguments

3. Variable Argument

The following example illustrates precedence. Assume a procedure declaration:

        proc p {{a A} args b {c C} d} {...}

This procedure requires at least two arguments, but can accept an unlimited number. The following table shows how various numbers of arguments are assigned. Values marked as `-` are assigned the default value.

Number of arguments | a | args | b | c | d
--- | --- | --- | --- | --- | ---
2 | - | - | 1 | - | 2
3 | 1 | - | 2 | - | 3
4 | 1 | - | 2 | 3 | 4
5 | 1 | 2 | 3 | 4 | 5
6 | 1 | 2,3 | 4 | 5 | 6

When `body` is being executed, variable names normally refer to local variables, which are created automatically when referenced and deleted when the procedure returns. One local variable is automatically created for each of the procedure’s arguments. Global variables can be accessed by invoking the `global` command or via the `::` prefix.

### New in Jim

In addition to procedure arguments, Jim procedures may declare static variables. These variables scoped to the procedure and initialised at procedure definition. Either from the static variable definition, or from the enclosing scope.

Consider the following example:

        . set a 1
        . proc a {} {a {b 2}} {
            set c 1
            puts "$a $b $c"
            incr a
            incr b
            incr c
        }
        . a
        1 2 1
        . a
        2 3 1

The static variable `a` has no initialiser, so it is initialised from the enclosing scope with the value 1. (Note that it is an error if there is no variable with the same name in the enclosing scope). However `b` has an initialiser, so it is initialised to 2.

Unlike a local variable, the value of a static variable is retained across invocations of the procedure.

See the `proc` command for information on how to define procedures and what happens when they are invoked. See also NAMESPACES.

## VARIABLES - SCALARS AND ARRAYS

Tcl allows the definition of variables and the use of their values either through $-style variable substitution, the `set` command, or a few other mechanisms.

Variables need not be declared: a new variable will automatically be created each time a new variable name is used.

Tcl supports two types of variables: scalars and arrays. A scalar variable has a single value, whereas an array variable can have any number of elements, each with a name (called its index) and a value.

Array indexes may be arbitrary strings; they need not be numeric. Parentheses are used refer to array elements in Tcl commands. For example, the command

        set x(first) 44

will modify the element of x whose index is first so that its new value is 44.

Two-dimensional arrays can be simulated in Tcl by using indexes that contain multiple concatenated values. For example, the commands

        set a(2,3) 1
        set a(3,6) 2

set the elements of a whose indexes are 2,3 and 3,6.

In general, array elements may be used anywhere in Tcl that scalar variables may be used.

If an array is defined with a particular name, then there may not be a scalar variable with the same name.

Similarly, if there is a scalar variable with a particular name then it is not possible to make array references to the variable.

To convert a scalar variable to an array or vice versa, remove the existing variable with the `unset` command.

The `array` command provides several features for dealing with arrays, such as querying the names of all the elements of the array and converting between an array and a list.

Variables may be either global or local. If a variable name is used when a procedure isn’t being executed, then it automatically refers to a global variable. Variable names used within a procedure normally refer to local variables associated with that invocation of the procedure. Local variables are deleted whenever a procedure exits. Either `global` command may be used to request that a name refer to a global variable for the duration of the current procedure (this is somewhat analogous to extern in C), or the variable may be explicitly scoped with the `::` prefix. For example

        . set a 1
        . set b 2
        . proc p {} {
            set c 3
            global a

            puts "$a $::b $c"
        }
        . p

will output:

    1 2 3

## ARRAYS AS LISTS IN JIM

Unlike Tcl, Jim can automatically convert between a list (with an even number of elements) and an array value. This is similar to the way Tcl can convert between a string and a list.

For example:

      set a {1 one 2 two}
      puts $a(2)

will output:

      two

Thus `array` `set` is equivalent to `set` when the variable does not exist or is empty.

The reverse is also true where an array will be converted into a list.

      set a(1) one; set a(2) two
      puts $a

will output:

      1 one 2 two

## DICTIONARY VALUES

Tcl 8.5 introduced the dict command, and Jim Tcl has added a version of this command. Dictionaries provide efficient access to key-value pairs, just like arrays, but dictionaries are pure values. This means that you can pass them to a procedure just as a list or a string. Tcl dictionaries are therefore much more like Tcl lists, except that they represent a mapping from keys to values, rather than an ordered sequence.

You can nest dictionaries, so that the value for a particular key consists of another dictionary. That way you can elegantly build complicated data structures, such as hierarchical databases. You can also combine dictionaries with other Tcl data structures. For instance, you can build a list of dictionaries that themselves contain lists.

Dictionaries are values that contain an efficient, order-preserving mapping from arbitrary keys to arbitrary values. Each key in the dictionary maps to a single value. They have a textual format that is exactly that of any list with an even number of elements, with each mapping in the dictionary being represented as two items in the list. When a command takes a dictionary and produces a new dictionary based on it (either returning it or writing it back into the variable that the starting dictionary was read from) the new dictionary will have the same order of keys, modulo any deleted keys and with new keys added on to the end. When a string is interpreted as a dictionary and it would otherwise have duplicate keys, only the last value for a particular key is used; the others are ignored, meaning that, "apple banana" and "apple carrot apple banana" are equivalent dictionaries (with different string representations).

Note that in Jim, arrays are implemented as dictionaries. Thus automatic conversion between lists and dictionaries applies as it does for arrays.

      . dict set a 1 one
      1 one
      . dict set a 2 two
      1 one 2 two
      . puts $a
      1 one 2 two
      . puts $a(2)
      two
      . dict set a 3 T three
      1 one 2 two 3 {T three}

See the `dict` command for more details.

## NAMESPACES

Tcl added namespaces as a mechanism avoiding name clashes, especially in applications including a number of 3rd party components. While there is less need for namespaces in Jim Tcl (which does not strive to support large applications), it is convenient to provide a subset of the support for namespaces to easy porting code from Tcl.

Jim Tcl currently supports "light-weight" namespaces which should be adequate for most purposes. This feature is currently experimental. See README.namespaces for more information and the documentation of the `namespace` command.

## GARBAGE COLLECTION, REFERENCES, LAMBDA FUNCTION

Unlike Tcl, Jim has some sophisticated support for functional programming. These are described briefly below.

More information may be found at http://wiki.tcl.tk/13847

### References

A reference can be thought of as holding a value with one level of indirection, where the value may be garbage collected when unreferenced. Consider the following example:

        . set r [ref "One String" test]
        <reference.<test___>.00000000000000000000>
        . getref $r
        One String

The operation `ref` creates a references to the value specified by the first argument. (The second argument is a "type" used for documentation purposes).

The operation `getref` is the dereferencing operation which retrieves the value stored in the reference.

        . setref $r "New String"
        New String
        . getref $r
        New String

The operation `setref` replaces the value stored by the reference. If the old value is no longer accessible by any reference, it will eventually be automatically be garbage collected.

### Garbage Collection

Normally, all values in Tcl are passed by value. As such values are copied and released automatically as necessary.

With the introduction of references, it is possible to create values whose lifetime transcend their scope. To support this, case, the Jim system will periodically identify and discard objects which are no longer accessible by any reference.

The `collect` command may be used to force garbage collection. Consider a reference created with a finalizer:

        . proc f {ref value} { puts "Finaliser called for $ref,$value" }
        . set r [ref "One String" test f]
        <reference.<test___>.00000000000
        . collect
        0
        . set r ""
        . collect
        Finaliser called for <reference.<test___>.00000000000,One String
        1

Note that once the reference, r, was modified so that it no longer contained a reference to the value, the garbage collector discarded the value (after calling the finalizer).

The finalizer for a reference may be examined or changed with the `finalize` command

        . finalize $r
        f
        . finalize $r newf
        newf

### Lambda Function

Jim provides a garbage collected `lambda` function. This is a procedure which is able to create an anonymous procedure. Consider:

        . set f [lambda {a} {{x 0}} { incr x $a }]
        . $f 1
        1
        . $f 2
        3
        . set f ""

This create an anonymous procedure (with the name stored in f), with a static variable which is incremented by the supplied value and the result returned.

Once the procedure name is no longer accessible, it will automatically be deleted when the garbage collector runs.

The procedure may also be delete immediately by renaming it "". e.g.

        . rename $f ""

## UTF-8 AND UNICODE

If Jim is built with UTF-8 support enabled (configure --enable-utf), then most string-related commands become UTF-8 aware. These include, but are not limited to, `string` `match`, `split`, `glob`, `scan` and `format`.

UTF-8 encoding has many advantages, but one of the complications is that characters can take a variable number of bytes. Thus the addition of `string` `bytelength` which returns the number of bytes in a string, while `string` `length` returns the number of characters.

If UTF-8 support is not enabled, all commands treat bytes as characters and `string` `bytelength` returns the same value as `string` `length`.

Note that even if UTF-8 support is not enabled, the `\uNNNN` and related syntax is still available to embed UTF-8 sequences.

Jim Tcl supports all currently defined unicode codepoints. That is 21 bits, up to +U+1FFFFF.

### String Matching

Commands such as `string` `match`, `lsearch` `-glob`, `array` `names` and others use string pattern matching rules. These commands support UTF-8. For example:

      string match a\[\ua0-\ubf\]b "a\u00a3b"

### format and scan

`format %c` allows a unicode codepoint to be be encoded. For example, the following will return a string with two bytes and one character. The same as `\ub5`

      format %c 0xb5

`format` respects widths as character widths, not byte widths. For example, the following will return a string with three characters, not three bytes.

      format %.3s \ub5\ub6\ub7\ub8

Similarly, `scan … %c` allows a UTF-8 to be decoded to a unicode codepoint. The following will set `a` to 181 (0xb5) and `b` to 65 (0x41).

      scan \u00b5A %c%c a b

`scan` `%s` will also accept a character class, including unicode ranges.

### String Classes

`string` `is` has not been extended to classify UTF-8 characters. Therefore, the following will return 0, even though the string may be considered to be alphabetic.

      string is alpha \ub5Test

This does not affect the string classes ascii, control, digit, double, integer or xdigit.

### Case Mapping and Conversion

Jim provides a simplified unicode case mapping. This means that case conversion and comparison will not increase or decrease the number of characters in a string. (Although it may change the number of bytes).

`string` `toupper` will convert any lowercase letters to their uppercase equivalent. Any character which is not a letter or has no uppercase equivalent is left unchanged. Similarly for `string` `tolower` and `string` `totitle`.

Commands which perform case insensitive matches, such as `string` `compare -nocase` and `lsearch` `-nocase` fold both strings to uppercase before comparison.

### Invalid UTF-8 Sequences

Some UTF-8 character sequences are invalid, such as those beginning with 0xff, those which represent character sequences longer than 3 bytes (greater than U+FFFF), and those which end prematurely, such as a lone 0xc2.

In these situations, the offending bytes are treated as single characters. For example, the following returns 2.

      string bytelength \xff\xff

### Regular Expressions

If UTF-8 support is enabled, the built-in regular expression engine will be selected which supports UTF-8 strings and patterns.

See REGULAR EXPRESSIONS

## BUILT-IN COMMANDS

The Tcl library provides the following built-in commands, which will be available in any application using Tcl. In addition to these built-in commands, there may be additional commands defined by each application, plus commands defined as Tcl procedures.

In the command syntax descriptions below, words in `boldface` are literals that you type verbatim to Tcl.

Words in `italics` are meta-symbols; they serve as names for any of a range of values that you can type.

Optional arguments or groups of arguments are indicated by enclosing them in `?question-marks?`.

Ellipses (`...`) indicate that any number of additional arguments or groups of arguments may appear, in the same format as the preceding argument(s).

### Command Index

`after` | `aio` | `alarm` | `alias` | `append` | `apply` | `array` | `binary`
`break` | `case` | `catch` | `cd` | `class` | `clock` | `close` | `collect`
`concat` | `continue` | `curry` | `defer` | `dict` | `env` | `eof` | `error`
`eval` | `eventloop` | `exec` | `exists` | `exit` | `expr` | `fconfigure` | `file`
`finalize` | `flush` | `for` | `foreach` | `format` | `getref` | `gets` | `glob`
`global` | `history` | `if` | `incr` | `info` | `interp` | `join` | `json::decode`
`json::encode` | `kill` | `lambda` | `lappend` | `lassign` | `lindex` | `linsert` | `list`
`llength` | `lmap` | `load` | `local` | `loop` | `lrange` | `lrepeat` | `lreplace`
`lreverse` | `lsearch` | `lset` | `lsort` | `namespace` | `oo` | `open` | `os.fork`
`os.gethostname` | `os.getids` | `os.uptime` | `pack` | `pack` | `package` | `pid` | `pipe`
`posix` | `proc` | `puts` | `pwd` | `rand` | `range` | `read` | `ref`
`regexp` | `regsub` | `rename` | `return` | `scan` | `seek` | `set` | `setref`
`signal` | `sleep` | `socket` | `source` | `split` | `stackdump` | `stacktrace` | `string`
`subst` | `super` | `switch` | `syslog` | `tailcall` | `tcl::autocomplete` | `tcl::prefix` | `tell`
`throw` | `time` | `tree` | `try` | `unknown` | `unpack` | `unset` | `upcall`
`update` | `uplevel` | `upvar` | `vwait` | `wait` | `while` | `zlib` |

### alarm

`alarm seconds`

Delivers the `SIGALRM` signal to the process after the given number of seconds. If the platform supports ualarm(3) then the argument may be a floating point value. Otherwise it must be an integer.

Note that unless a signal handler for `SIGALRM` has been installed (see `signal`), the process will exit on this signal.

### alias

`alias name args...`

Creates a single word alias (command) for one or more words. For example, the following creates an alias for the command `info` `exists`.

        alias e info exists
        if {[e var]} {
          ...
        }

`alias` returns `name`, allowing it to be used with `local`.

See also `proc`, `curry`, `lambda`, `local`, `info` `alias`, `exists` `-alias`

### append

`append varName value ?value value …?`

Append all of the `value` arguments to the current value of variable `varName`. If `varName` doesn’t exist, it is given a value equal to the concatenation of all the `value` arguments.

This command provides an efficient way to build up long variables incrementally. For example, "`append` `a $b`" is much more efficient than "`set` `a $a$b`" if `$a` is long.

### apply

`apply lambdaExpr ?arg1 arg2 ...?`

The command `apply` provides for anonymous procedure calls, similar to `lambda`, but without command name being created, even temporarily.

The function `lambdaExpr` is a two element list `{args body}` or a three element list `{args body namespace}`. The first element args specifies the formal arguments, in the same form as the `proc` and `lambda` commands.

### array

`array option arrayName ?arg...?`

This command performs one of several operations on the variable given by `arrayName`.

Note that in general, if the named array does not exist, the `array` command behaves as though the array exists but is empty.

The `option` argument determines what action is carried out by the command. The legal `options` (which may be abbreviated) are:

`array exists arrayName`

  Returns 1 if arrayName is an array variable, 0 if there is no variable by that name.

`array get arrayName ?pattern?`

  Returns a list containing pairs of elements. The first element in each pair is the name of an element in arrayName and the second element of each pair is the value of the array element. The order of the pairs is undefined. If pattern is not specified, then all of the elements of the array are included in the result. If pattern is specified, then only those elements whose names match pattern (using the matching rules of string match) are included. If arrayName isn’t the name of an array variable, or if the array contains no elements, then an empty list is returned.

`array names arrayName ?pattern?`

  Returns a list containing the names of all of the elements in the array that match pattern. If pattern is omitted then the command returns all of the element names in the array. If pattern is specified, then only those elements whose names match pattern (using the matching rules of string match) are included. If there are no (matching) elements in the array, or if arrayName isn’t the name of an array variable, then an empty string is returned.

`array set arrayName list`

  Sets the values of one or more elements in arrayName. list must have a form like that returned by array get, consisting of an even number of elements. Each odd-numbered element in list is treated as an element name within arrayName, and the following element in list is used as a new value for that array element. If the variable arrayName does not already exist and list is empty, arrayName is created with an empty array value.

`array size arrayName`

  Returns the number of elements in the array. If arrayName isn’t the name of an array then 0 is returned.

`array unset arrayName ?pattern?`

  Unsets all of the elements in the array that match pattern (using the matching rules of string match). If arrayName isn’t the name of an array variable or there are no matching elements in the array, no error will be raised. If pattern is omitted and arrayName is an array variable, then the command unsets the entire array. The command always returns an empty string.

### break

`break`

This command may be invoked only inside the body of a loop command such as `for` or `foreach` or `while`. It returns a `JIM_BREAK` code to signal the innermost containing loop command to return immediately.

### case

The obsolete `case` command has been removed from Jim Tcl since v0.75. Use `switch` instead.

### catch

`catch ?-?no?code ...? ?--? command ?resultVarName? ?optionsVarName?`

The `catch` command may be used to prevent errors from aborting command interpretation. `catch` evaluates `command`, and returns a `JIM_OK` code, regardless of any errors that might occur while executing `command` (with the possible exception of `JIM_SIGNAL` - see below).

The return value from `catch` is a decimal string giving the code returned by the Tcl interpreter after executing `command`. This will be 0 (`JIM_OK`) if there were no errors in `command`; otherwise it will have a non-zero value corresponding to one of the exceptional return codes (see jim.h for the definitions of code values, or the `info` `returncodes` command).

If the `resultVarName` argument is given, then it gives the name of a variable; `catch` will set the value of the variable to the string returned from `command` (either a result or an error message).

If the `optionsVarName` argument is given, then it gives the name of a variable; `catch` will set the value of the variable to a dictionary. For any return code other than `JIM_RETURN`, the value for the key `-code` will be set to the return code. For `JIM_RETURN` it will be set to the code given in `return` `-code`. Additionally, for the return code `JIM_ERR`, the value of the key `-errorinfo` will contain the current stack trace (the same result as `info` `stacktrace`), the value of the key `-errorcode` will contain the same value as the global variable $::errorCode, and the value of the key `-level` will be the current return level (see `return` `-level`). This can be useful to rethrow an error:

        if {[catch {...} msg opts]} {
            ...maybe do something with the error...
            incr opts(-level)
            return {*}$opts $msg
        }

Normally `catch` will `not` catch any of the codes `JIM_EXIT`, `JIM_EVAL` or `JIM_SIGNAL`. The set of codes which will be caught may be modified by specifying the one more codes before `command`.

e.g. To catch `JIM_EXIT` but not `JIM_BREAK` or `JIM_CONTINUE`

        catch -exit -nobreak -nocontinue -- { ... }

The use of `--` is optional. It signifies that no more return code options follow.

Note that if a signal marked as `signal` `handle` is caught with `catch` `-signal`, the return value (stored in `resultVarName`) is name of the signal caught.

### cd

`cd dirName`

Change the current working directory to `dirName`.

Returns an empty string.

This command can potentially be disruptive to an application, so it may be removed in some applications.

### clock

`clock seconds`

  Returns the current time as seconds since the epoch.

`clock clicks`

  Returns the current time in "clicks", a system-dependent, high-resolution time.

`clock microseconds`

  Returns the current time in microseconds.

`clock milliseconds`

  Returns the current time in milliseconds.

`clock format seconds ?-format format? ?-gmt boolean?`

  Format the given time (seconds since the epoch) according to the given format. See strftime(3) for supported formats. If no format is supplied, "%c" is used.

  If `boolean` is true, processing is performed in UTC. If `boolean` is false (the default), processing is performeed in the local time zone.

`clock scan str -format format ?-gmt boolean?`

  Scan the given time string using the given format string. See strptime(3) for supported formats. See `clock` `format` for the handling of -gmt.

### close

`close fileId`

`fileId close`

Closes the file given by `fileId`. `fileId` must be the return value from a previous invocation of the `open` command; after this command, it should not be used anymore.

### collect

`collect`

Normally reference garbage collection is automatically performed periodically. However it may be run immediately with the `collect` command.

See GARBAGE COLLECTION for more detail.

### concat

`concat arg ?arg ...?`

This command treats each argument as a list and concatenates them into a single list. It permits any number of arguments. For example, the command

        concat a b {c d e} {f {g h}}

will return

        a b c d e f {g h}

as its result.

### continue

`continue`

This command may be invoked only inside the body of a loop command such as `for` or `foreach` or `while`. It returns a `JIM_CONTINUE` code to signal the innermost containing loop command to skip the remainder of the loop’s body but continue with the next iteration of the loop.

### curry

`alias args...`

Similar to `alias` except it creates an anonymous procedure (lambda) instead of a named procedure.

the following creates a local, unnamed alias for the command `info` `exists`.

        set e [local curry info exists]
        if {[$e var]} {
          ...
        }

`curry` returns the name of the procedure.

See also `proc`, `alias`, `lambda`, `local`.

### dict

`dict option ?arg...?`

Performs one of several operations on dictionary values.

The `option` argument determines what action is carried out by the command. The legal `options` are:

`dict create ?key value ...?`

  Create and return a new dictionary value that contains each of the key/value mappings listed as arguments (keys and values alternating, with each key being followed by its associated value.)

`dict exists dictionary key ?key ...?`

  Returns a boolean value indicating whether the given key (or path of keys through a set of nested dictionaries) exists in the given dictionary value. This returns a true value exactly when `dict` `get` on that path will succeed.

`dict get dictionary ?key ...?`

  Given a dictionary value (first argument) and a key (second argument), this will retrieve the value for that key. Where several keys are supplied, the behaviour of the command shall be as if the result of "`dict` `get $dictVal $key`" was passed as the first argument to dict get with the remaining arguments as second (and possibly subsequent) arguments. This facilitates lookups in nested dictionaries. If no keys are provided, dict would return a list containing pairs of elements in a manner similar to array get. That is, the first element of each pair would be the key and the second element would be the value for that key. It is an error to attempt to retrieve a value for a key that is not present in the dictionary.

`dict keys dictionary ?pattern?`

  Returns a list of the keys in the dictionary. If pattern is specified, then only those keys whose names match `pattern` (using the matching rules of string match) are included.

`dict merge ?dictionary ...?`

  Return a dictionary that contains the contents of each of the `dictionary` arguments. Where two (or more) dictionaries contain a mapping for the same key, the resulting dictionary maps that key to the value according to the last dictionary on the command line containing a mapping for that key.

`dict set dictionaryName key ?key ...? value`

  This operation takes the `name` of a variable containing a dictionary value and places an updated dictionary value in that variable containing a mapping from the given key to the given value. When multiple keys are present, this operation creates or updates a chain of nested dictionaries.

`dict size dictionary`

  Return the number of key/value mappings in the given dictionary value.

`dict unset dictionaryName key ?key ...? value`

  This operation (the companion to `dict` `set`) takes the name of a variable containing a dictionary value and places an updated dictionary value in that variable that does not contain a mapping for the given key. Where multiple keys are present, this describes a path through nested dictionaries to the mapping to remove. At least one key must be specified, but the last key on the key-path need not exist. All other components on the path must exist.

`dict with dictionaryName key ?key ...? script`

  Execute the Tcl script in `script` with the value for each key in `dictionaryName` mapped to a variable with the same name. Where one or more keys are given, these indicate a chain of nested dictionaries, with the innermost dictionary being the one opened out for the execution of body. Making `dictionaryName` unreadable will make the updates to the dictionary be discarded, and this also happens if the contents of `dictionaryName` are adjusted so that the chain of dictionaries no longer exists. The result of `dict` `with` is (unless some kind of error occurs) the result of the evaluation of body.

  The variables are mapped in the scope enclosing the `dict` `with`; it is recommended that this command only be used in a local scope (procedure). Because of this, the variables set by `dict` `with` will continue to exist after the command finishes (unless explicitly unset). Note that changes to the contents of `dictionaryName` only happen when `script` terminates.

`dict for, values, incr, append, lappend, update, info, replace` to be documented…

### env

`env ?name? ?default?`

If `name` is supplied, returns the value of `name` from the initial environment (see getenv(3)). An error is returned if `name` does not exist in the environment, unless `default` is supplied - in which case that value is returned instead.

If no arguments are supplied, returns a list of all environment variables and their values as `{name value ...}`

See also the global variable `::env`

### eof

`eof fileId`

`fileId eof`

Returns 1 if an end-of-file condition has occurred on `fileId`, 0 otherwise.

`fileId` must have been the return value from a previous call to `open`, or it may be `stdin`, `stdout`, or `stderr` to refer to one of the standard I/O channels.

### error

`error message ?stacktrace?`

Returns a `JIM_ERR` code, which causes command interpretation to be unwound. `message` is a string that is returned to the application to indicate what went wrong.

If the `stacktrace` argument is provided and is non-empty, it is used to initialize the stacktrace.

This feature is most useful in conjunction with the `catch` command: if a caught error cannot be handled successfully, `stacktrace` can be used to return a stack trace reflecting the original point of occurrence of the error:

        catch {...} errMsg
        ...
        error $errMsg [info stacktrace]

See also `errorInfo`, `info` `stacktrace`, `catch` and `return`

### errorInfo

`errorInfo error ?stacktrace?`

Returns a human-readable representation of the given error message and stack trace. Typical usage is:

        if {[catch {...} error]} {
            puts stderr [errorInfo $error [info stacktrace]]
            exit 1
        }

See also `error`.

### eval

`eval arg ?arg...?`

`eval` takes one or more arguments, which together comprise a Tcl command (or collection of Tcl commands separated by newlines in the usual way). `eval` concatenates all its arguments in the same fashion as the `concat` command, passes the concatenated string to the Tcl interpreter recursively, and returns the result of that evaluation (or any error generated by it).

### exec

`exec arg ?arg...?`

This command treats its arguments as the specification of one or more UNIX commands to execute as subprocesses. The commands take the form of a standard shell pipeline; `|` arguments separate commands in the pipeline and cause standard output of the preceding command to be piped into standard input of the next command (or `|&` for both standard output and standard error).

Under normal conditions the result of the `exec` command consists of the standard output produced by the last command in the pipeline followed by the standard error output.

If any of the commands writes to its standard error file, then this will be included in the result after the standard output of the last command.

Note that unlike Tcl, data written to standard error does not cause `exec` to return an error.

If any of the commands in the pipeline exit abnormally or are killed or suspended, then `exec` will return an error. If no standard error output was produced, or is redirected, the error message will include the normal result, as above, followed by error messages describing the abnormal terminations.

If any standard error output was produced, these abnormal termination messages are suppressed.

If the last character of the result or error message is a newline then that character is deleted from the result or error message for consistency with normal Tcl return values.

An `arg` may have one of the following special forms:

`>filename`

  The standard output of the last command in the pipeline is redirected to the file. In this situation `exec` will normally return an empty string.

`>>filename`

  As above, but append to the file.

`>@fileId`

  The standard output of the last command in the pipeline is redirected to the given (writable) file descriptor (e.g. stdout, stderr, or the result of `open`). In this situation `exec` will normally return an empty string.

`2>filename`

  The standard error of the last command in the pipeline is redirected to the file.

`2>>filename`

  As above, but append to the file.

`2>@fileId`

  The standard error of the last command in the pipeline is redirected to the given (writable) file descriptor.

`2>@1`

  The standard error of the last command in the pipeline is redirected to the same file descriptor as the standard output.

`>&filename`

  Both the standard output and standard error of the last command in the pipeline is redirected to the file.

`>>&filename`

  As above, but append to the file.

`<filename`

  The standard input of the first command in the pipeline is taken from the file.

`<<string`

  The standard input of the first command is taken as the given immediate value.

`<@fileId`

  The standard input of the first command in the pipeline is taken from the given (readable) file descriptor.

If there is no redirection of standard input, standard error or standard output, these are connected to the corresponding input or output of the application.

If the last `arg` is `&` then the command will be executed in background. In this case the standard output from the last command in the pipeline will go to the application’s standard output unless redirected in the command, and error output from all the commands in the pipeline will go to the application’s standard error file. The return value of exec in this case is a list of process ids (pids) in the pipeline.

Each `arg` becomes one word for a command, except for `|`, `<`, `<<`, `>`, and `&` arguments, and the arguments that follow `<`, `<<`, and `>`.

The first word in each command is taken as the command name; the directories in the PATH environment variable are searched for an executable by the given name.

No `glob` expansion or other shell-like substitutions are performed on the arguments to commands.

If the command fails, the global $::errorCode (and the -errorcode option in `catch`) will be set to a list, as follows:

`CHILDKILLED pid sigName msg`

  This format is used when a child process has been killed because of a signal. The pid element will be the process’s identifier (in decimal). The sigName element will be the symbolic name of the signal that caused the process to terminate; it will be one of the names from the include file signal.h, such as SIGPIPE. The msg element will be a short human-readable message describing the signal, such as "write on pipe with no readers" for SIGPIPE.

`CHILDSUSP pid sigName msg`

  This format is used when a child process has been suspended because of a signal. The pid element will be the process’s identifier, in decimal. The sigName element will be the symbolic name of the signal that caused the process to suspend; this will be one of the names from the include file signal.h, such as SIGTTIN. The msg element will be a short human-readable message describing the signal, such as "background tty read" for SIGTTIN.

`CHILDSTATUS pid code`

  This format is used when a child process has exited with a non-zero exit status. The pid element will be the process’s identifier (in decimal) and the code element will be the exit code returned by the process (also in decimal).

The environment for the executed command is set from $::env (unless this variable is unset, in which case the original environment is used).

### exists

`exists ?-var|-proc|-command|-alias? name`

Checks the existence of the given variable, procedure, command or alias respectively and returns 1 if it exists or 0 if not. This command provides a more simplified/convenient version of `info` `exists`, `info` `procs` and `info` `commands`.

If the type is omitted, a type of -var is used. The type may be abbreviated.

### exit

`exit ?returnCode?`

Terminate the process, returning `returnCode` to the parent as the exit status.

If `returnCode` isn’t specified then it defaults to 0.

Note that exit can be caught with `catch`.

### expr

`expr arg`

Calls the expression processor to evaluate `arg`, and returns the result as a string. See the section EXPRESSIONS above.

Note that Jim supports a shorthand syntax for `expr` as `$(...)` The following two are identical.

      set x [expr {3 * 2 + 1}]
      set x $(3 * 2 + 1)

### file

`file option name ?arg...?`

Operate on a file or a file name. `name` is the name of a file.

`option` indicates what to do with the file name. Any unique abbreviation for `option` is acceptable. The valid options are:

`file atime name`

  Return a decimal string giving the time at which file `name` was last accessed. The time is measured in the standard UNIX fashion as seconds from a fixed starting time (often January 1, 1970). If the file doesn’t exist or its access time cannot be queried then an error is generated.

`file copy ?-force? source target`

  Copies file `source` to file `target`. The source file must exist. The target file must not exist, unless `-force` is specified.

`file delete ?-force? ?--? name...`

  Deletes file or directory `name`. If the file or directory doesn’t exist, nothing happens. If it can’t be deleted, an error is generated. Non-empty directories will not be deleted unless the `-force` options is given. In this case no errors will be generated, even if the file/directory can’t be deleted. Use `--` if there is any possibility of the first name being `-force`.

`file dirname name`

  Return all of the characters in `name` up to but not including the last slash character. If there are no slashes in `name` then return `.` (a single dot). If the last slash in `name` is its first character, then return `/`.

`file executable name`

  Return 1 if file `name` is executable by the current user, 0 otherwise.

`file exists name`

  Return 1 if file `name` exists and the current user has search privileges for the directories leading to it, 0 otherwise.

`file extension name`

  Return all of the characters in `name` after and including the last dot in `name`. If there is no dot in `name` then return the empty string.

`file isdirectory name`

  Return 1 if file `name` is a directory, 0 otherwise.

`file isfile name`

  Return 1 if file `name` is a regular file, 0 otherwise.

`file join arg...`

  Joins multiple path components. Note that if any components is an absolute path, the preceding components are ignored. Thus `"`file` join /tmp /root"` returns `"/root"`.

`file link ?-hard|-symbolic? newname target`

  Creates a hard link (default) or symbolic link from `newname` to `target`. Note that the sense of this command is the opposite of `file` `rename` and `file` `copy` and also of `ln`, but this is compatible with Tcl. An error is returned if `target` doesn’t exist or `newname` already exists.

`file lstat name varName`

  Same as stat option (see below) except uses the `lstat` kernel call instead of `stat`. This means that if `name` refers to a symbolic link the information returned in `varName` is for the link rather than the file it refers to. On systems that don’t support symbolic links this option behaves exactly the same as the stat option.

`file mkdir dir1 ?dir2...?`

  Creates each directory specified. For each pathname `dir` specified, this command will create all non-existing parent directories as well as `dir` itself. If an existing directory is specified, then no action is taken and no error is returned. Trying to overwrite an existing file with a directory will result in an error. Arguments are processed in the order specified, halting at the first error, if any.

`file mtime name ?time?`

  Return a decimal string giving the time at which file `name` was last modified. The time is measured in the standard UNIX fashion as seconds from a fixed starting time (often January 1, 1970). If the file doesn’t exist or its modified time cannot be queried then an error is generated. If `time` is given, sets the modification time of the file to the given value.

`file mtimeus name ?time_us?`

  As for `file` `mtime` except the time value is in microseconds since the epoch (see also `clock` `microseconds`). Note that some platforms and some filesystems don’t support high resolution timestamps for files.

`file normalize name`

  Return the normalized path of `name`. See realpath(3).

`file owned name`

  Return 1 if file `name` is owned by the current user, 0 otherwise.

`file readable name`

  Return 1 if file `name` is readable by the current user, 0 otherwise.

`file readlink name`

  Returns the value of the symbolic link given by `name` (i.e. the name of the file it points to). If `name` isn’t a symbolic link or its value cannot be read, then an error is returned. On systems that don’t support symbolic links this option is undefined.

`file rename ?-force? oldname newname`

  Renames the file from the old name to the new name. If `newname` already exists, an error is returned unless `-force` is specified.

`file rootname name`

  Return all of the characters in `name` up to but not including the last . character in the name. If `name` doesn’t contain a dot, then return `name`.

`file split name`

  Returns a list whose elements are the path components in `name`. The first element of the list will have the same path type as `name`. All other elements will be relative. Path separators will be discarded.

`file stat name ?varName?`

  Invoke the stat kernel call on `name`, and return the result as a dictionary with the following keys: atime, ctime, dev, gid, ino, mode, mtime, nlink, size, type, uid, mtimeus (if supported - see `file` `mtimeus`) Each element except type is a decimal string with the value of the corresponding field from the stat return structure; see the manual entry for stat for details on the meanings of the values. The type element gives the type of the file in the same form returned by the command `file` `type`. If `varName` is specified, it is taken to be the name of an array variable and the values are also stored into the array.

`file tail name`

  Return all of the characters in `name` after the last slash. If `name` contains no slashes then return `name`.

`file tempfile ?template?`

  Creates and returns the name of a unique temporary file. If `template` is omitted, a default template will be used to place the file in /tmp. See mkstemp(3) for the format of the template and security concerns.

`file type name`

  Returns a string giving the type of file `name`, which will be one of `file`, `directory`, `characterSpecial`, `blockSpecial`, `fifo`, `link`, or `socket`.

`file writable name`

  Return 1 if file `name` is writable by the current user, 0 otherwise.

The `file` commands that return 0/1 results are often used in conditional or looping commands, for example:

        if {![file exists foo]} {
            error {bad file name}
        } else {
            ...
        }

### finalize

`finalize reference ?command?`

If `command` is omitted, returns the finalizer command for the given reference.

Otherwise, sets a new finalizer command for the given reference. `command` may be the empty string to remove the current finalizer.

The reference must be a valid reference create with the `ref` command.

See GARBAGE COLLECTION for more detail.

### flush

`flush fileId`

`fileId flush`

Flushes any output that has been buffered for `fileId`. `fileId` must have been the return value from a previous call to `open`, or it may be `stdout` or `stderr` to access one of the standard I/O streams; it must refer to a file that was opened for writing. This command returns an empty string.

### for

`for start test next body`

`for` is a looping command, similar in structure to the C `for` statement. The `start`, `next`, and `body` arguments must be Tcl command strings, and `test` is an expression string.

The `for` command first invokes the Tcl interpreter to execute `start`. Then it repeatedly evaluates `test` as an expression; if the result is non-zero it invokes the Tcl interpreter on `body`, then invokes the Tcl interpreter on `next`, then repeats the loop. The command terminates when `test` evaluates to 0.

If a `continue` command is invoked within `body` then any remaining commands in the current execution of `body` are skipped; processing continues by invoking the Tcl interpreter on `next`, then evaluating `test`, and so on.

If a `break` command is invoked within `body` or `next`, then the `for` command will return immediately.

The operation of `break` and `continue` are similar to the corresponding statements in C.

`for` returns an empty string.

### foreach

`foreach varName list body`

`foreach varList list ?varList2 list2 ...? body`

In this command, `varName` is the name of a variable, `list` is a list of values to assign to `varName`, and `body` is a collection of Tcl commands.

For each field in `list` (in order from left to right), `foreach` assigns the contents of the field to `varName` (as if the `lindex` command had been used to extract the field), then calls the Tcl interpreter to execute `body`.

If instead of being a simple name, `varList` is used, multiple assignments are made each time through the loop, one for each element of `varList`.

For example, if there are two elements in `varList` and six elements in the list, the loop will be executed three times.

If the length of the list doesn’t evenly divide by the number of elements in `varList`, the value of the remaining variables in the last iteration of the loop are undefined.

The `break` and `continue` statements may be invoked inside `body`, with the same effect as in the `for` command.

`foreach` returns an empty string.

### format

`format formatString ?arg ...?`

This command generates a formatted string in the same way as the C sprintf procedure (it uses sprintf in its implementation). `formatString` indicates how to format the result, using `%` fields as in sprintf, and the additional arguments, if any, provide values to be substituted into the result.

All of the sprintf options are valid; see the sprintf man page for details. Each `arg` must match the expected type from the `%` field in `formatString`; the `format` command converts each argument to the correct type (floating, integer, etc.) before passing it to sprintf for formatting.

The only unusual conversion is for `%c`; in this case the argument must be a decimal string, which will then be converted to the corresponding ASCII (or UTF-8) character value.

In addition, Jim Tcl provides basic support for conversion to binary with `%b`.

`format` does backslash substitution on its `formatString` argument, so backslash sequences in `formatString` will be handled correctly even if the argument is in braces.

The return value from `format` is the formatted string.

### getref

`getref reference`

Returns the string associated with `reference`. The reference must be a valid reference create with the `ref` command.

See GARBAGE COLLECTION for more detail.

### gets

`gets fileId ?varName?`

`fileId gets ?varName?`

Reads the next line from the file given by `fileId` and discards the terminating newline character.

If `varName` is specified, then the line is placed in the variable by that name and the return value is a count of the number of characters read (not including the newline).

If the end of the file is reached before reading any characters then -1 is returned and `varName` is set to an empty string.

If `varName` is not specified then the return value will be the line (minus the newline character) or an empty string if the end of the file is reached before reading any characters.

An empty string will also be returned if a line contains no characters except the newline, so `eof` may have to be used to determine what really happened.

If the last character in the file is not a newline character, then `gets` behaves as if there were an additional newline character at the end of the file.

`fileId` must be `stdin` or the return value from a previous call to `open`; it must refer to a file that was opened for reading.

### glob

`glob ?-nocomplain? ?-directory dir? ?-tails? ?--? pattern ?pattern ...?`

This command performs filename globbing, using csh rules. The returned value from `glob` is the list of expanded filenames.

If `-nocomplain` is specified as the first argument then an empty list may be returned; otherwise an error is returned if the expanded list is empty. The `-nocomplain` argument must be provided exactly: an abbreviation will not be accepted.

If `-directory` is given, the `dir` is understood to contain a directory name to search in. This allows globbing inside directories whose names may contain glob-sensitive characters. The returned names include the directory name unless `-tails` is specified.

If `-tails` is specified, along with `-directory`, the returned names are relative to the given directory.

### global

`global varName ?varName ...?`

This command is ignored unless a Tcl procedure is being interpreted. If so, then it declares each given `varName` to be a global variable rather than a local one. For the duration of the current procedure (and only while executing in the current procedure), any reference to `varName` will be bound to a global variable instead of a local one.

An alternative to using `global` is to use the `::` prefix to explicitly name a variable in the global scope.

### if

`if expr1 ?then? body1 elseif expr2 ?then? body2 elseif ... ?else? ?bodyN?`

The `if` command evaluates `expr1` as an expression (in the same way that `expr` evaluates its argument). The value of the expression must be numeric; if it is non-zero then `body1` is executed by passing it to the Tcl interpreter.

Otherwise `expr2` is evaluated as an expression and if it is non-zero then `body2` is executed, and so on.

If none of the expressions evaluates to non-zero then `bodyN` is executed.

The `then` and `else` arguments are optional "noise words" to make the command easier to read.

There may be any number of `elseif` clauses, including zero. `bodyN` may also be omitted as long as `else` is omitted too.

The return value from the command is the result of the body script that was executed, or an empty string if none of the expressions was non-zero and there was no `bodyN`.

### incr

`incr varName ?increment?`

Increment the value stored in the variable whose name is `varName`. The value of the variable must be integral.

If `increment` is supplied then its value (which must be an integer) is added to the value of variable `varName`; otherwise 1 is added to `varName`.

The new value is stored as a decimal string in variable `varName` and also returned as result.

If the variable does not exist, the variable is implicitly created and set to `0` first.

### info

`info option ?arg...?`

  Provide information about various internals to the Tcl interpreter. The legal `option`'s (which may be abbreviated) are:

`info args procname`

  Returns a list containing the names of the arguments to procedure `procname`, in order. `procname` must be the name of a Tcl command procedure.

`info alias command`

  `command` must be an alias created with `alias`. In which case the target command and arguments, as passed to `alias` are returned. See `exists` `-alias`

`info body procname`

  Returns the body of procedure `procname`. `procname` must be the name of a Tcl command procedure.

`info channels`

  Returns a list of all open file handles from `open` or `socket`

`info commands ?pattern?`

  If `pattern` isn’t specified, returns a list of names of all the Tcl commands, including both the built-in commands written in C and the command procedures defined using the `proc` command. If `pattern` is specified, only those names matching `pattern` are returned. Matching is determined using the same rules as for `string` `match`.

`info complete command ?missing?`

  Returns 1 if `command` is a complete Tcl command in the sense of having no unclosed quotes, braces, brackets or array element names, If the command doesn’t appear to be complete then 0 is returned. This command is typically used in line-oriented input environments to allow users to type in commands that span multiple lines; if the command isn’t complete, the script can delay evaluating it until additional lines have been typed to complete the command. If `varName` is specified, the missing character is stored in the variable with that name.

`info exists varName`

  Returns 1 if the variable named `varName` exists in the current context (either as a global or local variable), returns 0 otherwise.

`info frame ?number?`

  If `number` is not specified, this command returns a number which is the same result as `info` `level` - the current stack frame level. If `number` is specified, then the result is a list consisting of the procedure, filename and line number for the procedure call at level `number` on the stack. If `number` is positive then it selects a particular stack level (1 refers to the top-most active procedure, 2 to the procedure it called, and so on); otherwise it gives a level relative to the current level (0 refers to the current procedure, -1 to its caller, and so on). The level has an identical meaning to `info` `level`.

`info globals ?pattern?`

  If `pattern` isn’t specified, returns a list of all the names of currently-defined global variables. If `pattern` is specified, only those names matching `pattern` are returned. Matching is determined using the same rules as for `string` `match`.

`info hostname`

  An alias for `os.gethostname` for compatibility with Tcl 6.x

`info level ?number?`

  If `number` is not specified, this command returns a number giving the stack level of the invoking procedure, or 0 if the command is invoked at top-level. If `number` is specified, then the result is a list consisting of the name and arguments for the procedure call at level `number` on the stack. If `number` is positive then it selects a particular stack level (1 refers to the top-most active procedure, 2 to the procedure it called, and so on); otherwise it gives a level relative to the current level (0 refers to the current procedure, -1 to its caller, and so on). See the `uplevel` command for more information on what stack levels mean.

`info locals ?pattern?`

  If `pattern` isn’t specified, returns a list of all the names of currently-defined local variables, including arguments to the current procedure, if any. Variables defined with the `global` and `upvar` commands will not be returned. If `pattern` is specified, only those names matching `pattern` are returned. Matching is determined using the same rules as for `string` `match`.

`info nameofexecutable`

  Returns the name of the binary file from which the application was invoked. A full path will be returned, unless the path can’t be determined, in which case the empty string will be returned.

`info procs ?pattern?`

  If `pattern` isn’t specified, returns a list of all the names of Tcl command procedures. If `pattern` is specified, only those names matching `pattern` are returned. Matching is determined using the same rules as for `string` `match`.

`info references`

  Returns a list of all references which have not yet been garbage collected.

`info returncodes ?code?`

  Returns a list representing the mapping of standard return codes to names. e.g. `{0 ok 1 error 2 return ...}`. If a code is given, instead returns the name for the given code.

`info script`

  If a Tcl script file is currently being evaluated (i.e. there is a call to Jim_EvalFile active or there is an active invocation of the `source` command), then this command returns the name of the innermost file being processed. Otherwise the command returns an empty string.

`info source script ?filename line?`

  With a single argument, returns the original source location of the given script as a list of `{filename linenumber}`. If the source location can’t be determined, the list `{{} 0}` is returned. If `filename` and `line` are given, returns a copy of `script` with the associate source information. This can be useful to produce useful messages from `eval`, etc. if the original source information may be lost.

`info stacktrace`

  After an error is caught with `catch`, returns the stack trace as a list of `{procedure filename line ...}`.

`info statics procname`

  Returns a dictionary of the static variables of procedure `procname`. `procname` must be the name of a Tcl command procedure. An empty dictionary is returned if the procedure has no static variables.

`info version`

  Returns the version number for this version of Jim in the form `x.yy`.

`info vars ?pattern?`

  If `pattern` isn’t specified, returns a list of all the names of currently-visible variables, including both locals and currently-visible globals. If `pattern` is specified, only those names matching `pattern` are returned. Matching is determined using the same rules as for `string` `match`.

### join

`join list ?joinString?`

The `list` argument must be a valid Tcl list. This command returns the string formed by joining all of the elements of `list` together with `joinString` separating each adjacent pair of elements.

The `joinString` argument defaults to a space character.

### kill

`kill ?SIG|-0? pid`

Sends the given signal to the process identified by `pid`.

The signal may be specified by name or number in one of the following forms:

- `TERM`

- `SIGTERM`

- `-TERM`

- `15`

- `-15`

The signal name may be in either upper or lower case.

The special signal name `-0` simply checks that a signal `could` be sent.

If no signal is specified, SIGTERM is used.

An error is raised if the signal could not be delivered.

### lambda

`lambda args ?statics? body`

The `lambda` command is identical to `proc`, except rather than creating a named procedure, it creates an anonymous procedure and returns the name of the procedure.

See `proc` and GARBAGE COLLECTION for more detail.

### lappend

`lappend varName value ?value value ...?`

Treat the variable given by `varName` as a list and append each of the `value` arguments to that list as a separate element, with spaces between elements.

If `varName` doesn’t exist, it is created as a list with elements given by the `value` arguments. `lappend` is similar to `append` except that each `value` is appended as a list element rather than raw text.

This command provides a relatively efficient way to build up large lists. For example,

        lappend a $b

is much more efficient than

        set a [concat $a [list $b]]

when `$a` is long.

### lassign

`lassign list varName ?varName ...?`

This command treats the value `list` as a list and assigns successive elements from that list to the variables given by the `varName` arguments in order. If there are more variable names than list elements, the remaining variables are set to the empty string. If there are more list elements than variables, a list of unassigned elements is returned.

        . lassign {1 2 3} a b; puts a=$a,b=$b
        3
        a=1,b=2

### local

`local cmd ?arg...?`

First, `local` evaluates `cmd` with the given arguments. The return value must be the name of an existing command, which is marked as having local scope. This means that when the current procedure exits, the specified command is deleted. This can be useful with `lambda`, local procedures or to automatically close a filehandle.

In addition, if a command already exists with the same name, the existing command will be kept rather than deleted, and may be called via `upcall`. The previous command will be restored when the current procedure exits. See `upcall` for more details.

In this example, a local procedure is created. Note that the procedure continues to have global scope while it is active.

        proc outer {} {
          # proc ... returns "inner" which is marked local
          local proc inner {} {
            # will be deleted when 'outer' exits
          }

          inner
          ...
        }

In this example, the lambda is deleted at the end of the procedure rather than waiting until garbage collection.

        proc outer {} {
          set x [lambda inner {args} {
            # will be deleted when 'outer' exits
          }]
          # Use 'function' here which simply returns $x
          local function $x

          $x ...
          ...
        }

### loop

`loop var first limit ?incr? body`

Similar to `for` except simpler and possibly more efficient. With a positive increment, equivalent to:

        for {set var $first} {$var < $limit} {incr var $incr} $body

If `incr` is not specified, 1 is used. Note that setting the loop variable inside the loop does not affect the loop count.

### lindex

`lindex list ?index …?`

Treats `list` as a Tcl list and returns element `index` from it (0 refers to the first element of the list). See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `index`.

In extracting the element, `lindex` observes the same rules concerning braces and quotes and backslashes as the Tcl command interpreter; however, variable substitution and command substitution do not occur.

If no index values are given, simply returns `list`

If `index` is negative or greater than or equal to the number of elements in `list`, then an empty string is returned.

If additional index arguments are supplied, then each argument is used in turn to select an element from the previous indexing operation, allowing the script to select elements from sublists.

### linsert

`linsert list index element ?element element ...?`

This command produces a new list from `list` by inserting all of the `element` arguments just before the element `index` of `list`. Each `element` argument will become a separate element of the new list. If `index` is less than or equal to zero, then the new elements are inserted at the beginning of the list. If `index` is greater than or equal to the number of elements in the list, then the new elements are appended to the list.

See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `index`.

### list

`list arg ?arg ...?`

This command returns a list comprised of all the arguments, `arg`. Braces and backslashes get added as necessary, so that the `lindex` command may be used on the result to re-extract the original arguments, and also so that `eval` may be used to execute the resulting list, with `arg1` comprising the command’s name and the other args comprising its arguments. `list` produces slightly different results than `concat`: `concat` removes one level of grouping before forming the list, while `list` works directly from the original arguments. For example, the command

        list a b {c d e} {f {g h}}

will return

        a b {c d e} {f {g h}}

while `concat` with the same arguments will return

        a b c d e f {g h}

### llength

`llength list`

Treats `list` as a list and returns a decimal string giving the number of elements in it.

### lset

`lset varName ?index ..? newValue`

Sets an element in a list.

The `lset` command accepts a parameter, `varName`, which it interprets as the name of a variable containing a Tcl list. It also accepts zero or more indices into the list. Finally, it accepts a new value for an element of varName. If no indices are presented, the command takes the form:

        lset varName newValue

In this case, newValue replaces the old value of the variable varName.

When presented with a single index, the `lset` command treats the content of the varName variable as a Tcl list. It addresses the index’th element in it (0 refers to the first element of the list). When interpreting the list, `lset` observes the same rules concerning braces and quotes and backslashes as the Tcl command interpreter; however, variable substitution and command substitution do not occur. The command constructs a new list in which the designated element is replaced with newValue. This new list is stored in the variable varName, and is also the return value from the `lset` command.

If index is negative or greater than or equal to the number of elements in $varName, then an error occurs.

See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `index`.

If additional index arguments are supplied, then each argument is used in turn to address an element within a sublist designated by the previous indexing operation, allowing the script to alter elements in sublists. The command,

        lset a 1 2 newValue

replaces element 2 of sublist 1 with `newValue`.

The integer appearing in each index argument must be greater than or equal to zero. The integer appearing in each index argument must be strictly less than the length of the corresponding list. In other words, the `lset` command cannot change the size of a list. If an index is outside the permitted range, an error is reported.

### lmap

`lmap varName list body`

`lmap varList list ?varList2 list2 ...? body`

`lmap` is a "collecting" `foreach` which returns a list of its results.

For example:

        . lmap i {1 2 3 4 5} {expr $i*$i}
        1 4 9 16 25
        . lmap a {1 2 3} b {A B C} {list $a $b}
        {1 A} {2 B} {3 C}

If the body invokes `continue`, no value is added for this iteration. If the body invokes `break`, the loop ends and no more values are added.

### load

`load filename`

Loads the dynamic extension, `filename`. Generally the filename should have the extension `.so`. The initialisation function for the module must be based on the name of the file. For example loading `hwaccess.so` will invoke the initialisation function, `Jim_hwaccessInit`. Normally the `load` command should not be used directly. Instead it is invoked automatically by `package` `require`.

### lrange

`lrange list first last`

`list` must be a valid Tcl list. This command will return a new list consisting of elements `first` through `last`, inclusive.

See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `first` and `last`.

If `last` is greater than or equal to the number of elements in the list, then it is treated as if it were `end`.

If `first` is greater than `last` then an empty string is returned.

Note: `"`lrange` list first first"` does not always produce the same result as `"`lindex` list first"` (although it often does for simple fields that aren’t enclosed in braces); it does, however, produce exactly the same results as `"`list` [`lindex` list first]"`

### lreplace

`lreplace list first last ?element element ...?`

Returns a new list formed by replacing one or more elements of `list` with the `element` arguments.

`first` gives the index in `list` of the first element to be replaced.

If `first` is less than zero then it refers to the first element of `list`; the element indicated by `first` must exist in the list.

`last` gives the index in `list` of the last element to be replaced; it must be greater than or equal to `first`.

See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `first` and `last`.

The `element` arguments specify zero or more new arguments to be added to the list in place of those that were deleted.

Each `element` argument will become a separate element of the list.

If no `element` arguments are specified, then the elements between `first` and `last` are simply deleted.

### lrepeat

`lrepeat number element1 ?element2 ...?`

Build a list by repeating elements `number` times (which must be a positive integer).

        . lrepeat 3 a b
        a b a b a b

### lreverse

`lreverse list`

Returns the list in reverse order.

        . lreverse {1 2 3}
        3 2 1

### lsearch

`lsearch ?options? list pattern`

This command searches the elements `list` to see if one of them matches `pattern`. If so, the command returns the index of the first matching element (unless the options `-all`, `-inline` or `-bool` are specified.) If not, the command returns -1. The option arguments indicates how the elements of the list are to be matched against pattern and must have one of the values below:

Note that this command is different from Tcl in that default match type is `-exact` rather than `-glob`.

`-exact`

  `pattern` is a literal string that is compared for exact equality against each list element. This is the default.

`-glob`

  `pattern` is a glob-style pattern which is matched against each list element using the same rules as the string match command.

`-regexp`

  `pattern` is treated as a regular expression and matched against each list element using the rules described by `regexp`.

`-command cmdname`

  `cmdname` is a command which is used to match the pattern against each element of the list. It is invoked as `cmdname ?-nocase? pattern listvalue` and should return 1 for a match, or 0 for no match.

`-all`

  Changes the result to be the list of all matching indices (or all matching values if `-inline` is specified as well). If indices are returned, the indices will be in numeric order. If values are returned, the order of the values will be the order of those values within the input list.

`-inline`

  The matching value is returned instead of its index (or an empty string if no value matches). If `-all` is also specified, then the result of the command is the list of all values that matched. The `-inline` and `-bool` options are mutually exclusive.

`-bool`

  Changes the result to 1 if a match was found, or 0 otherwise. If `-all` is also specified, the result will be a list of 0 and 1 for each element of the list depending upon whether the corresponding element matches. The `-inline` and `-bool` options are mutually exclusive.

`-not`

  This negates the sense of the match, returning the index (or value if `-inline` is specified) of the first non-matching value in the list. If `-bool` is also specified, the 0 will be returned if a match is found, or 1 otherwise. If `-all` is also specified, non-matches will be returned rather than matches.

`-nocase`

  Causes comparisons to be handled in a case-insensitive manner.

### lsort

`lsort ?-index listindex? ?-nocase|-integer|-real|-command cmdname? ?-unique? ?-decreasing|-increasing? list`

Sort the elements of `list`, returning a new list in sorted order. By default, ASCII (or UTF-8) sorting is used, with the result in increasing order.

If `-nocase` is specified, comparisons are case-insensitive.

If `-integer` is specified, numeric sorting is used.

If `-real` is specified, floating point number sorting is used.

If `-command cmdname` is specified, `cmdname` is treated as a command name. For each comparison, `cmdname $value1 $value2` is called which should compare the values and return an integer less than, equal to, or greater than zero if the `$value1` is to be considered less than, equal to, or greater than `$value2`, respectively.

If `-decreasing` is specified, the resulting list is in the opposite order to what it would be otherwise. `-increasing` is the default.

If `-unique` is specified, then only the last set of duplicate elements found in the list will be retained. Note that duplicates are determined relative to the comparison used in the sort. Thus if `-index 0` is used, `{1 a}` and `{1 b}` would be considered duplicates and only the second element, `{1 b}`, would be retained.

If `-index listindex` is specified, each element of the list is treated as a list and the given index is extracted from the list for comparison. The list index may be any valid list index, such as `1`, `end` or `end-2`.

### defer

`defer script`

This command is a simple helper command to add a script to the `$jim::defer` variable that will run when the current proc or interpreter exits. For example:

        . proc a {} { defer {puts "Leaving a"}; puts "Exit" }
        . a
        Exit
        Leaving a

If the `$jim::defer` variable exists, it is treated as a list of scripts to run when the proc or interpreter exits.

### open

`open fileName ?access?`

`open |command-pipeline ?access?`

Opens a file and returns an identifier that may be used in future invocations of commands like `read`, `puts`, and `close`. `fileName` gives the name of the file to open.

The `access` argument indicates the way in which the file is to be accessed. It may have any of the following values:

`r`

  Open the file for reading only; the file must already exist.

`r`+

  Open the file for both reading and writing; the file must already exist.

`w`

  Open the file for writing only. Truncate it if it exists. If it doesn’t exist, create a new file.

`w`+

  Open the file for reading and writing. Truncate it if it exists. If it doesn’t exist, create a new file.

`a`

  Open the file for writing only. The file must already exist, and the file is positioned so that new data is appended to the file.

`a`+

  Open the file for reading and writing. If the file doesn’t exist, create a new empty file. Set the initial access position to the end of the file.

`access` defaults to r.

If a file is opened for both reading and writing, then `seek` must be invoked between a read and a write, or vice versa.

If the first character of `fileName` is "|" then the remaining characters of `fileName` are treated as a list of arguments that describe a command pipeline to invoke, in the same style as the arguments for exec. In this case, the channel identifier returned by open may be used to write to the command’s input pipe or read from its output pipe, depending on the value of `access`. If write-only access is used (e.g. `access` is w), then standard output for the pipeline is directed to the current standard output unless overridden by the command. If read-only access is used (e.g. `access` is r), standard input for the pipeline is taken from the current standard input unless overridden by the command.

The `pid` command may be used to return the process ids of the commands forming the command pipeline.

See also `socket`, `pid`, `exec`

### package

`package provide name ?version?`

Indicates that the current script provides the package named `name`. If no version is specified, 1.0 is used.

Any script which provides a package may include this statement as the first statement, although it is not required.

`package require name ?version?*`

Searches for the package with the given `name` by examining each path in $::auto_path and trying to load $path/$name.so as a dynamic extension, or $path/$name.tcl as a script package.

The first such file which is found is considered to provide the package. (The version number is ignored).

If $name.so exists, it is loaded with the `load` command, otherwise if $name.tcl exists it is loaded with the `source` command.

If `load` or `source` fails, `package` `require` will fail immediately. No further attempt will be made to locate the file.

### pid

`pid`

`pid fileId`

The first form returns the process identifier of the current process.

The second form accepts a handle returned by `open` and returns a list of the process ids forming the pipeline in the same form as `exec` `... &`. If fileId represents a regular file handle rather than a command pipeline, the empty string is returned instead.

See also `open`, `exec`

### proc

`proc name args ?statics? body`

The `proc` command creates a new Tcl command procedure, `name`. When the new command is invoked, the contents of `body` will be executed. Tcl interpreter. `args` specifies the formal arguments to the procedure. If specified, `statics`, declares static variables which are bound to the procedure.

See <<_procedures,PROCEDURES> for detailed information about Tcl procedures.

The `proc` command returns `name` (which is useful with `local`).

When a procedure is invoked, the procedure’s return value is the value specified in a `return` command. If the procedure doesn’t execute an explicit `return`, then its return value is the value of the last command executed in the procedure’s body.

If an error occurs while executing the procedure body, then the procedure-as-a-whole will return that same error.

### puts

`puts ?-nonewline? ?fileId? string`

`fileId puts ?-nonewline? string`

Writes the characters given by `string` to the file given by `fileId`. `fileId` must have been the return value from a previous call to `open`, or it may be `stdout` or `stderr` to refer to one of the standard I/O channels; it must refer to a file that was opened for writing.

In the first form, if no `fileId` is specified then it defaults to `stdout`. `puts` normally outputs a newline character after `string`, but this feature may be suppressed by specifying the `-nonewline` switch.

Output to files is buffered internally by Tcl; the `flush` command may be used to force buffered characters to be output.

### pipe

Creates a pair of `aio` channels and returns the handles as a list: `{read write}`

        lassign [pipe] r w

        # Must close $w after exec
        exec ps >@$w &
        $w close

        $r readable ...

### pwd

`pwd`

Returns the path name of the current working directory.

### rand

`rand ?min? ?max?`

Returns a random integer between `min` (defaults to 0) and `max` (defaults to the maximum integer).

If only one argument is given, it is interpreted as `max`.

### range

`range ?start? end ?step?`

Returns a list of integers starting at `start` (defaults to 0) and ranging up to but not including `end` in steps of `step` defaults to 1).

        . range 5
        0 1 2 3 4
        . range 2 5
        2 3 4
        . range 2 10 4
        2 6
        . range 7 4 -2
        7 5

### read

`read ?-nonewline? fileId`

`fileId read ?-nonewline?`

`read fileId numBytes`

`fileId read numBytes`

In the first form, all of the remaining bytes are read from the file given by `fileId`; they are returned as the result of the command. If the `-nonewline` switch is specified then the last character of the file is discarded if it is a newline.

In the second form, the extra argument specifies how many bytes to read; exactly this many bytes will be read and returned, unless there are fewer than `numBytes` bytes left in the file; in this case, all the remaining bytes are returned.

`fileId` must be `stdin` or the return value from a previous call to `open`; it must refer to a file that was opened for reading.

### regexp

`regexp ?-nocase? ?-line? ?-indices? ?-start offset? ?-all? ?-inline? ?--? exp string ?matchVar? ?subMatchVar subMatchVar ...?`

Determines whether the regular expression `exp` matches part or all of `string` and returns 1 if it does, 0 if it doesn’t.

See REGULAR EXPRESSIONS above for complete information on the syntax of `exp` and how it is matched against `string`.

If additional arguments are specified after `string` then they are treated as the names of variables to use to return information about which part(s) of `string` matched `exp`. `matchVar` will be set to the range of `string` that matched all of `exp`. The first `subMatchVar` will contain the characters in `string` that matched the leftmost parenthesized subexpression within `exp`, the next `subMatchVar` will contain the characters that matched the next parenthesized subexpression to the right in `exp`, and so on.

Normally, `matchVar` and the each `subMatchVar` are set to hold the matching characters from `string`, however see `-indices` and `-inline` below.

If there are more values for `subMatchVar` than parenthesized subexpressions within `exp`, or if a particular subexpression in `exp` doesn’t match the string (e.g. because it was in a portion of the expression that wasn’t matched), then the corresponding `subMatchVar` will be set to `"-1 -1"` if `-indices` has been specified or to an empty string otherwise.

The following switches modify the behaviour of `regexp`

`-nocase`

  Causes upper-case and lower-case characters to be treated as identical during the matching process.

`-line`

  Use newline-sensitive matching. By default, newline is a completely ordinary character with no special meaning in either REs or strings. With this flag, `[` bracket expressions and `.` never match newline, an `` anchor matches the null string after any newline in the string in addition to its normal function, and the `$` anchor matches the null string before any newline in the string in addition to its normal function.

`-indices`

  Changes what is stored in the subMatchVars. Instead of storing the matching characters from string, each variable will contain a list of two decimal strings giving the indices in string of the first and last characters in the matching range of characters.

`-start offset`

  Specifies a character index offset into the string at which to start matching the regular expression. If `-indices` is specified, the indices will be indexed starting from the absolute beginning of the input string. `offset` will be constrained to the bounds of the input string.

`-all`

  Causes the regular expression to be matched as many times as possible in the string, returning the total number of matches found. If this is specified with match variables, they will contain information for the last match only.

`-inline`

  Causes the command to return, as a list, the data that would otherwise be placed in match variables. When using `-inline`, match variables may not be specified. If used with `-all`, the list will be concatenated at each iteration, such that a flat list is always returned. For each match iteration, the command will append the overall match data, plus one element for each subexpression in the regular expression.

`--`

  Marks the end of switches. The argument following this one will be treated as `exp` even if it starts with a `-`.

### regsub

`regsub ?-nocase? ?-all? ?-line? ?-start offset? ?--? exp string subSpec ?varName?`

This command matches the regular expression `exp` against `string` using the rules described in REGULAR EXPRESSIONS above.

If `varName` is specified, the commands stores `string` to `varName` with the substitutions detailed below, and returns the number of substitutions made (normally 1 unless `-all` is specified). This is 0 if there were no matches.

If `varName` is not specified, the substituted string will be returned instead.

When copying `string`, the portion of `string` that matched `exp` is replaced with `subSpec`. If `subSpec` contains a `&` or `\0`, then it is replaced in the substitution with the portion of `string` that matched `exp`.

If `subSpec` contains a `\n`, where `n` is a digit between 1 and 9, then it is replaced in the substitution with the portion of `string` that matched the `n`'-th parenthesized subexpression of `exp`. Additional backslashes may be used in `subSpec` to prevent special interpretation of `&` or `\0` or `\n` or backslash.

The use of backslashes in `subSpec` tends to interact badly with the Tcl parser’s use of backslashes, so it’s generally safest to enclose `subSpec` in braces if it includes backslashes.

The following switches modify the behaviour of `regsub`

`-nocase`

  Upper-case characters in `string` are converted to lower-case before matching against `exp`; however, substitutions specified by `subSpec` use the original unconverted form of `string`.

`-all`

  All ranges in `string` that match `exp` are found and substitution is performed for each of these ranges, rather than only the first. The `&` and `\n` sequences are handled for each substitution using the information from the corresponding match.

`-line`

  Use newline-sensitive matching. By default, newline is a completely ordinary character with no special meaning in either REs or strings. With this flag, `[` bracket expressions and `.` never match newline, an `` anchor matches the null string after any newline in the string in addition to its normal function, and the `$` anchor matches the null string before any newline in the string in addition to its normal function.

`-start offset`

  Specifies a character index offset into the string at which to start matching the regular expression. `offset` will be constrained to the bounds of the input string.

`--`

  Marks the end of switches. The argument following this one will be treated as `exp` even if it starts with a `-`.

### ref

`ref string tag ?finalizer?`

Create a new reference containing `string` of type `tag`. If `finalizer` is specified, it is a command which will be invoked when the a garbage collection cycle runs and this reference is no longer accessible.

The finalizer is invoked as:

        finalizer reference string

See GARBAGE COLLECTION for more detail.

### rename

`rename oldName newName`

Rename the command that used to be called `oldName` so that it is now called `newName`. If `newName` is an empty string (e.g. {}) then `oldName` is deleted. The `rename` command returns an empty string as result.

### return

`return ?-code code? ?-errorinfo stacktrace? ?-errorcode errorcode? ?-level n? ?value?`

Return immediately from the current procedure (or top-level command or `source` command), with `value` as the return value. If `value` is not specified, an empty string will be returned as result.

If `-code` is specified (as either a number or ok, error, break, continue, signal, return or exit), this code will be used instead of `JIM_OK`. This is generally useful when implementing flow of control commands.

If `-level` is specified and greater than 1, it has the effect of delaying the new return code from `-code`. This is useful when rethrowing an error from `catch`. See the implementation of try/catch in tclcompat.tcl for an example of how this is done.

Note: The following options are only used when `-code` is JIM_ERR.

If `-errorinfo` is specified (as returned from `info` `stacktrace`) it is used to initialize the stacktrace.

If `-errorcode` is specified, it is used to set the global variable $::errorCode.

### scan

`scan string format varName1 ?varName2 ...?`

This command parses fields from an input string in the same fashion as the C sscanf procedure. `string` gives the input to be parsed and `format` indicates how to parse it, using % fields as in sscanf. All of the sscanf options are valid; see the sscanf man page for details. Each `varName` gives the name of a variable; when a field is scanned from `string`, the result is converted back into a string and assigned to the corresponding `varName`. The only unusual conversion is for %c. For %c conversions a single character value is converted to a decimal string, which is then assigned to the corresponding `varName`; no field width may be specified for this conversion.

### seek

`seek fileId offset ?origin?`

`fileId seek offset ?origin?`

Change the current access position for `fileId`. The `offset` and `origin` arguments specify the position at which the next read or write will occur for `fileId`. `offset` must be a number (which may be negative) and `origin` must be one of the following:

`start`

  The new access position will be `offset` bytes from the start of the file.

`current`

  The new access position will be `offset` bytes from the current access position; a negative `offset` moves the access position backwards in the file.

`end`

  The new access position will be `offset` bytes from the end of the file. A negative `offset` places the access position before the end-of-file, and a positive `offset` places the access position after the end-of-file.

The `origin` argument defaults to `start`.

`fileId` must have been the return value from a previous call to `open`, or it may be `stdin`, `stdout`, or `stderr` to refer to one of the standard I/O channels.

This command returns an empty string.

### set

`set varName ?value?`

Returns the value of variable `varName`.

If `value` is specified, then set the value of `varName` to `value`, creating a new variable if one doesn’t already exist, and return its value.

If `varName` contains an open parenthesis and ends with a close parenthesis, then it refers to an array element: the characters before the open parenthesis are the name of the array, and the characters between the parentheses are the index within the array. Otherwise `varName` refers to a scalar variable.

If no procedure is active, then `varName` refers to a global variable.

If a procedure is active, then `varName` refers to a parameter or local variable of the procedure, unless the `global` command has been invoked to declare `varName` to be global.

The `::` prefix may also be used to explicitly reference a variable in the global scope.

### setref

`setref reference string`

Store a new string in `reference`, replacing the existing string. The reference must be a valid reference create with the `ref` command.

See GARBAGE COLLECTION for more detail.

### signal

Command for signal handling.

See `kill` for the different forms which may be used to specify signals.

Commands which return a list of signal names do so using the canonical form: "`SIGINT SIGTERM`".

`signal handle ?signals ...?`

  If no signals are given, returns a list of all signals which are currently being handled. If signals are specified, these are added to the list of signals currently being handled.

`signal ignore ?signals ...?`

  If no signals are given, returns a lists all signals which are currently being ignored. If signals are specified, these are added to the list of signals currently being ignored. These signals are still delivered, but are not considered by `catch` `-signal` or `try` `-signal`. Use `signal` `check` to determine which signals have occurred but been ignored.

`signal block ?signals ...?`

  If no signals are given, returns a lists all signals which are currently being blocked. If signals are specified, these are added to the list of signals currently being blocked. These signals are not delivered to the process. This can be useful for signals such as `SIGPIPE`, especially in conjunction with `exec` as child processes inherit the parent’s signal disposition.

`signal default ?signals ...?`

  If no signals are given, returns a lists all signals which currently have the default behaviour. If signals are specified, these are added to the list of signals which have the default behaviour.

`signal check ?-clear? ?signals ...?`

  Returns a list of signals which have been delivered to the process but are ignored. If signals are specified, only that set of signals will be checked, otherwise all signals will be checked. If `-clear` is specified, any signals returned are removed and will not be returned by subsequent calls to `signal` `check` unless delivered again.

`signal throw ?signal?`

  Raises the given signal, which defaults to `SIGINT` if not specified. The behaviour is identical to:

        kill signal [pid]

Note that `signal` `handle` and `signal` `ignore` represent two forms of signal handling. `signal` `handle` is used in conjunction with `catch` `-signal` or `try` `-signal` to immediately abort execution when the signal is delivered. Alternatively, `signal` `ignore` is used in conjunction with `signal` `check` to handle signal synchronously. Consider the two examples below.

Prevent a processing from taking too long

        signal handle SIGALRM
        alarm 20
        try -signal {
            .. possibly long running process ..
            alarm 0
        } on signal {sig} {
            puts stderr "Process took too long"
        }

Handle SIGHUP to reconfigure:

        signal ignore SIGHUP
        while {1} {
            ... handle configuration/reconfiguration ...
            while {[signal check -clear SIGHUP] eq ""} {
                ... do processing ..
            }
            # Received SIGHUP, so reconfigure
        }

Note: signal handling is currently not supported in child interpreters. In these interpreters, the signal command does not exist.

### sleep

`sleep seconds`

Pauses for the given number of seconds, which may be a floating point value less than one to sleep for less than a second, or an integer to sleep for one or more seconds.

### source

`source fileName`

Read file `fileName` and pass the contents to the Tcl interpreter as a sequence of commands to execute in the normal fashion. The return value of `source` is the return value of the last command executed from the file. If an error occurs in executing the contents of the file, then the `source` command will return that error.

If a `return` command is invoked from within the file, the remainder of the file will be skipped and the `source` command will return normally with the result from the `return` command.

### split

`split string ?splitChars?`

Returns a list created by splitting `string` at each character that is in the `splitChars` argument.

Each element of the result list will consist of the characters from `string` between instances of the characters in `splitChars`.

Empty list elements will be generated if `string` contains adjacent characters in `splitChars`, or if the first or last character of `string` is in `splitChars`.

If `splitChars` is an empty string then each character of `string` becomes a separate element of the result list.

`splitChars` defaults to the standard white-space characters. For example,

        split "comp.unix.misc" .

returns `"comp unix misc"` and

        split "Hello world" {}

returns `"H e l l o { } w o r l d"`.

### stackdump

`stackdump stacktrace`

Creates a human readable representation of a stack trace.

### stacktrace

`stacktrace`

Returns a live stack trace as a list of `proc file line proc file line ...`. Iteratively uses `info` `frame` to create the stack trace. This stack trace is in the same form as produced by `catch` and `info` `stacktrace`

See also `stackdump`.

### string

`string option arg ?arg ...?`

Perform one of several string operations, depending on `option`. The legal options (which may be abbreviated) are:

`string bytelength string`

  Returns the length of the string in bytes. This will return the same value as `string` `length` if UTF-8 support is not enabled, or if the string is composed entirely of ASCII characters. See UTF-8 AND UNICODE.

`string byterange string first last`

  Like `string` `range` except works on bytes rather than characters. These commands are identical if UTF-8 support is not enabled.

`string cat ?string1 string2 ...?`

  Concatenates the given strings into a single string.

`string compare ?-nocase? ?-length len? string1 string2`

  Perform a character-by-character comparison of strings `string1` and `string2` in the same way as the C strcmp procedure. Return -1, 0, or 1, depending on whether `string1` is lexicographically less than, equal to, or greater than `string2`. If `-length` is specified, then only the first `len` characters are used in the comparison. If `len` is negative, it is ignored. Performs a case-insensitive comparison if `-nocase` is specified.

`string equal ?-nocase? ?-length len? string1 string2`

  Returns 1 if the strings are equal, or 0 otherwise. If `-length` is specified, then only the first `len` characters are used in the comparison. If `len` is negative, it is ignored. Performs a case-insensitive comparison if `-nocase` is specified.

`string first string1 string2 ?firstIndex?`

  Search `string2` for a sequence of characters that exactly match the characters in `string1`. If found, return the index of the first character in the first such match within `string2`. If not found, return -1. If `firstIndex` is specified, matching will start from `firstIndex` of `string1`.

  See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `firstIndex`.

`string index string charIndex`

  Returns the `charIndex`th character of the `'string` argument. A `charIndex` of 0 corresponds to the first character of the string. If `charIndex` is less than 0 or greater than or equal to the length of the string then an empty string is returned.

  See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `charIndex`.

`string is class ?-strict? string`

  Returns 1 if `string` is a valid member of the specified character class, otherwise returns 0. If `-strict` is specified, then an empty string returns 0, otherwise an empty string will return 1 on any class. The following character classes are recognized (the class name can be abbreviated):

  `alnum`

    Any alphabet or digit character.

  `alpha`

    Any alphabet character.

  `ascii`

    Any character with a value less than 128 (those that are in the 7-bit ascii range).

  `boolean`

    Any of the valid string formats for a boolean value in Tcl (0, false, no, off, 1, true, yes, on)

  `control`

    Any control character.

  `digit`

    Any digit character.

  `double`

    Any of the valid forms for a double in Tcl, with optional surrounding whitespace. In case of under/overflow in the value, 0 is returned.

  `graph`

    Any printing character, except space.

  `integer`

    Any of the valid string formats for an integer value in Tcl, with optional surrounding whitespace.

  `lower`

    Any lower case alphabet character.

  `print`

    Any printing character, including space.

  `punct`

    Any punctuation character.

  `space`

    Any space character.

  `upper`

    Any upper case alphabet character.

  `xdigit`

    Any hexadecimal digit character ([0-9A-Fa-f]).

  Note that string classification does `not` respect UTF-8. See UTF-8 AND UNICODE.

  Note that only `lowercase` boolean values are recognized (Tcl accepts any case).

`string last string1 string2 ?lastIndex?`

  Search `string2` for a sequence of characters that exactly match the characters in `string1`. If found, return the index of the first character in the last such match within `string2`. If there is no match, then return -1. If `lastIndex` is specified, only characters up to `lastIndex` of `string2` will be considered in the match.

  See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `lastIndex`.

`string length string`

  Returns a decimal string giving the number of characters in `string`. If UTF-8 support is enabled, this may be different than the number of bytes. See UTF-8 AND UNICODE.

`string map ?-nocase? mapping string`

  Replaces substrings in `string` based on the key-value pairs in `mapping`, which is a list of `key value key value ...` as in the form returned by `array` `get`. Each instance of a key in the string will be replaced with its corresponding value. If `-nocase` is specified, then matching is done without regard to case differences. Both key and value may be multiple characters. Replacement is done in an ordered manner, so the key appearing first in the list will be checked first, and so on. `string` is only iterated over once, so earlier key replacements will have no affect for later key matches. For example,

          string map {abc 1 ab 2 a 3 1 0} 1abcaababcabababc

  will return the string `01321221`.

  Note that if an earlier key is a prefix of a later one, it will completely mask the later one. So if the previous example is reordered like this,

          string map {1 0 ab 2 a 3 abc 1} 1abcaababcabababc

  it will return the string `02c322c222c`.

`string match ?-nocase? pattern string`

  See if `pattern` matches `string`; return 1 if it does, 0 if it doesn’t. Matching is done in a fashion similar to that used by the C-shell. For the two strings to match, their contents must be identical except that the following special sequences may appear in `pattern`:

  `*`

    Matches any sequence of characters in `string`, including a null string.

  `?`

    Matches any single character in `string`.

  `[chars]`

    Matches any character in the set given by `chars`. If a sequence of the form `x-y` appears in `chars`, then any character between `x` and `y`, inclusive, will match.

  `\x`

    Matches the single character `x`. This provides a way of avoiding the special interpretation of the characters `\*?[]` in `pattern`.

  Performs a case-insensitive comparison if `-nocase` is specified.

`string range string first last`

  Returns a range of consecutive characters from `string`, starting with the character whose index is `first` and ending with the character whose index is `last`. An index of 0 refers to the first character of the string.

  See STRING AND LIST INDEX SPECIFICATIONS for all allowed forms for `first` and `last`.

  If `first` is less than zero then it is treated as if it were zero, and if `last` is greater than or equal to the length of the string then it is treated as if it were `end`. If `first` is greater than `last` then an empty string is returned.

`string repeat string count`

  Returns a new string consisting of `string` repeated `count` times.

`string replace string first last ?newstring?`

  Removes a range of consecutive characters from `string`, starting with the character whose index is `first` and ending with the character whose index is `last`. If `newstring` is specified, then it is placed in the removed character range. If `first` is less than zero then it is treated as if it were zero, and if `last` is greater than or equal to the length of the string then it is treated as if it were `end`. If `first` is greater than `last` or the length of the initial string, or `last` is less than 0, then the initial string is returned untouched.

`string reverse string`

  Returns a string that is the same length as `string` but with its characters in the reverse order.

`string tolower string`

  Returns a value equal to `string` except that all upper case letters have been converted to lower case.

`string totitle string`

  Returns a value equal to `string` except that the first character is converted to title case (or upper case if there is no UTF-8 titlecase variant) and all remaining characters have been converted to lower case.

`string toupper string`

  Returns a value equal to `string` except that all lower case letters have been converted to upper case.

`string trim string ?chars?`

  Returns a value equal to `string` except that any leading or trailing characters from the set given by `chars` are removed. If `chars` is not specified then white space is removed (spaces, tabs, newlines, and carriage returns).

`string trimleft string ?chars?`

  Returns a value equal to `string` except that any leading characters from the set given by `chars` are removed. If `chars` is not specified then white space is removed (spaces, tabs, newlines, and carriage returns).

`string trimright string ?chars?`

  Returns a value equal to `string` except that any trailing characters from the set given by `chars` are removed. If `chars` is not specified then white space is removed (spaces, tabs, newlines, and carriage returns). Null characters are always removed.

### subst

`subst ?-nobackslashes? ?-nocommands? ?-novariables? string`

This command performs variable substitutions, command substitutions, and backslash substitutions on its string argument and returns the fully-substituted result. The substitutions are performed in exactly the same way as for Tcl commands. As a result, the string argument is actually substituted twice, once by the Tcl parser in the usual fashion for Tcl commands, and again by the subst command.

If any of the `-nobackslashes`, `-nocommands`, or `-novariables` are specified, then the corresponding substitutions are not performed. For example, if `-nocommands` is specified, no command substitution is performed: open and close brackets are treated as ordinary characters with no special interpretation.

Note: when it performs its substitutions, subst does not give any special treatment to double quotes or curly braces. For example, the following script returns `xyz {44}`, not `xyz {$a}`.

        set a 44
        subst {xyz {$a}}

### switch

`switch ?options? string pattern body ?pattern body ...?`

`switch ?options? string {pattern body ?pattern body ...?}`

The `switch` command matches its string argument against each of the pattern arguments in order. As soon as it finds a pattern that matches string it evaluates the following body and returns the result of that evaluation. If the last pattern argument is default then it matches anything. If no pattern argument matches string and no default is given, then the `switch` command returns an empty string. If the initial arguments to switch start with - then they are treated as options. The following options are currently supported:

`-exact`

  Use exact matching when comparing string to a pattern. This is the default.

`-glob`

  When matching string to the patterns, use glob-style matching (i.e. the same as implemented by the string match command).

`-regexp`

  When matching string to the patterns, use regular expression matching (i.e. the same as implemented by the regexp command).

`-command commandname`

  When matching string to the patterns, use the given command, which must be a single word. The command is invoked as commandname pattern string, or commandname -nocase pattern string and must return 1 if matched, or 0 if not.

`--`

  Marks the end of options. The argument following this one will be treated as string even if it starts with a `-`.

Two syntaxes are provided for the pattern and body arguments. The first uses a separate argument for each of the patterns and commands; this form is convenient if substitutions are desired on some of the patterns or commands. The second form places all of the patterns and commands together into a single argument; the argument must have proper list structure, with the elements of the list being the patterns and commands. The second form makes it easy to construct multi-line `switch` commands, since the braces around the whole list make it unnecessary to include a backslash at the end of each line. Since the pattern arguments are in braces in the second form, no command or variable substitutions are performed on them; this makes the behaviour of the second form different than the first form in some cases.

If a body is specified as `-` it means that the body for the next pattern should also be used as the body for this pattern (if the next pattern also has a body of `-` then the body after that is used, and so on). This feature makes it possible to share a single body among several patterns.

Below are some examples of `switch` commands:

        switch abc a - b {format 1} abc {format 2} default {format 3}

will return 2,

        switch -regexp aaab {
               ^a.*b$ -
               b {format 1}
               a* {format 2}
               default {format 3}
        }

will return 1, and

        switch xyz {
               a -
               b {format 1}
               a* {format 2}
               default {format 3}
        }

will return 3.

### tailcall

`tailcall cmd ?arg...?`

The `tailcall` command provides an optimised way of invoking a command whilst replacing the current call frame. This is similar to exec in Bourne Shell.

The following are identical except the first immediately replaces the current call frame.

      tailcall a b c

      return [uplevel 1 [list a b c]]

`tailcall` is useful as a dispatch mechanism:

      proc a {cmd args} {
        tailcall sub_$cmd {*}$args
      }
      proc sub_cmd1 ...
      proc sub_cmd2 ...

### tell

`tell fileId`

`fileId tell`

Returns a decimal string giving the current access position in `fileId`.

`fileId` must have been the return value from a previous call to `open`, or it may be `stdin`, `stdout`, or `stderr` to refer to one of the standard I/O channels.

### throw

`throw code ?msg?`

This command throws an exception (return) code along with an optional message. This command is mostly for convenient usage with `try`.

The command `throw break` is equivalent to `break`. The command `throw 20 message` can be caught with an `on 20 ...` clause to `try`.

### time

`time command ?count?`

This command will call the Tcl interpreter `count` times to execute `command` (or once if `count` isn’t specified). It will then return a string of the form

        503 microseconds per iteration

which indicates the average amount of time required per iteration, in microseconds.

Time is measured in elapsed time, not CPU time.

### try

`try ?catchopts? tryscript ?on returncodes {?resultvar? ?optsvar?} handlerscript ...? ?finally finalscript?`

The `try` command is provided as a convenience for exception handling.

This interpeter first evaluates `tryscript` under the effect of the catch options `catchopts` (e.g. `-signal -noexit --`, see `catch`).

It then evaluates the script for the first matching on handler (there many be zero or more) based on the return code from the `try` section. For example a normal `JIM_ERR` error will be matched by an on error handler.

Finally, any `finalscript` is evaluated.

The result of this command is the result of `tryscript`, except in the case where an exception occurs in a matching on handler script or the finally script, in which case the result is this new exception.

The specified `returncodes` is a list of return codes either as names (ok, error, break, etc.) or as integers.

If `resultvar` and `optsvar` are specified, they are set as for `catch` before evaluating the matching handler.

For example:

        set f [open input]
        try -signal {
            process $f
        } on {continue break} {} {
            error "Unexpected break/continue"
        } on error {msg opts} {
            puts "Dealing with error"
            return {*}$opts $msg
        } on signal sig {
            puts "Got signal: $sig"
        } finally {
            $f close
        }

If break, continue or error are raised, they are dealt with by the matching handler.

In any case, the file will be closed via the finally clause.

See also `throw`, `catch`, `return`, `error`.

### unknown

`unknown cmdName ?arg arg …?`

This command doesn’t actually exist as part of Tcl, but Tcl will invoke it if it does exist.

If the Tcl interpreter encounters a command name for which there is not a defined command, then Tcl checks for the existence of a command named `unknown`.

If there is no such command, then the interpreter returns an error.

If the `unknown` command exists, then it is invoked with arguments consisting of the fully-substituted name and arguments for the original non-existent command.

The `unknown` command typically does things like searching through library directories for a command procedure with the name `cmdName`, or expanding abbreviated command names to full-length, or automatically executing unknown commands as UNIX sub-processes.

In some cases (such as expanding abbreviations) `unknown` will change the original command slightly and then (re-)execute it. The result of the `unknown` command is used as the result for the original non-existent command.

### unset

`unset ?-nocomplain? ?--? ?name name …?`

Remove variables. Each `name` is a variable name, specified in any of the ways acceptable to the `set` command.

If a `name` refers to an element of an array, then that element is removed without affecting the rest of the array.

If a `name` consists of an array name with no parenthesized index, then the entire array is deleted.

The `unset` command returns an empty string as result.

An error occurs if any of the variables doesn’t exist, unless -nocomplain is specified. The -- argument may be specified to stop option processing in case the variable name may be -nocomplain.

### upcall

`upcall command ?args …?`

May be used from within a proc defined as `local` `proc` in order to call the previous, hidden version of the same command.

If there is no previous definition of the command, an error is returned.

### uplevel

`uplevel ?level? command ?command …?`

All of the `command` arguments are concatenated as if they had been passed to `concat`; the result is then evaluated in the variable context indicated by `level`. `uplevel` returns the result of that evaluation. If `level` is an integer, then it gives a distance (up the procedure calling stack) to move before executing the command. If `level` consists of `#` followed by a number then the number gives an absolute level number. If `level` is omitted then it defaults to `1`. `level` cannot be defaulted if the first `command` argument starts with a digit or `#`.

For example, suppose that procedure a was invoked from top-level, and that it called b, and that b called c. Suppose that c invokes the `uplevel` command. If `level` is `1` or `#2` or omitted, then the command will be executed in the variable context of b. If `level` is `2` or `#1` then the command will be executed in the variable context of a.

If `level` is 3 or `#0` then the command will be executed at top-level (only global variables will be visible). The `uplevel` command causes the invoking procedure to disappear from the procedure calling stack while the command is being executed. In the above example, suppose c invokes the command

        uplevel 1 {set x 43; d}

where d is another Tcl procedure. The `set` command will modify the variable x in b’s context, and 'd will execute at level 3, as if called from b. If it in turn executes the command

        uplevel {set x 42}

then the `set` command will modify the same variable x in b’s context: the procedure 'c does not appear to be on the call stack when d is executing. The command `info` `level` may be used to obtain the level of the current procedure.

`uplevel` makes it possible to implement new control constructs as Tcl procedures (for example, `uplevel` could be used to implement the `while` construct as a Tcl procedure).

### upvar

`upvar ?level? otherVar myVar ?otherVar myVar …?`

This command arranges for one or more local variables in the current procedure to refer to variables in an enclosing procedure call or to global variables.

`level` may have any of the forms permitted for the `uplevel` command, and may be omitted if the first letter of the first `otherVar` isn’t `#` or a digit (it defaults to 1).

For each `otherVar` argument, `upvar` makes the variable by that name in the procedure frame given by `level` (or at global level, if `level` is `#0`) accessible in the current procedure by the name given in the corresponding `myVar` argument.

The variable named by `otherVar` need not exist at the time of the call; it will be created the first time `myVar` is referenced, just like an ordinary variable.

`upvar` may only be invoked from within procedures.

`upvar` returns an empty string.

The `upvar` command simplifies the implementation of call-by-name procedure calling and also makes it easier to build new control constructs as Tcl procedures. For example, consider the following procedure:

        proc add2 name {
            upvar $name x
            set x [expr $x+2]
        }

add2 is invoked with an argument giving the name of a variable, and it adds two to the value of that variable. Although add2 could have been implemented using `uplevel` instead of `upvar`, `upvar` makes it simpler for add2 to access the variable in the caller’s procedure frame.

### wait

`wait`

`wait -nohang pid`

With no arguments, cleans up any processes started by `exec` `... &` that have completed (reaps zombie processes).

With one or two arguments, waits for a process by id, either returned by `exec` `... &` or by `os.fork` (if supported).

Waits for the process to complete, unless `-nohang` is specified, in which case returns immediately if the process is still running.

Returns a list of 3 elements.

`{NONE x x}` if the process does not exist or has already been waited for, or if -nohang is specified, and the process is still alive.

`{CHILDSTATUS <pid> <exit-status>}` if the process exited normally.

`{CHILDKILLED <pid> <signal>}` if the process terminated on a signal.

`{CHILDSUSP <pid> none}` if the process terminated for some other reason.

Note that on platforms supporting waitpid(2), `pid` can also be given special values such as 0 or -1. See waitpid(2) for more detail.

### while

`while test body`

The `while` command evaluates `test` as an expression (in the same way that `expr` evaluates its argument). The value of the expression must be numeric; if it is non-zero then `body` is executed by passing it to the Tcl interpreter.

Once `body` has been executed then `test` is evaluated again, and the process repeats until eventually `test` evaluates to a zero numeric value. `continue` commands may be executed inside `body` to terminate the current iteration of the loop, and `break` commands may be executed inside `body` to cause immediate termination of the `while` command.

The `while` command always returns an empty string.

## OPTIONAL-EXTENSIONS

The following extensions may or may not be available depending upon what options were selected when Jim Tcl was built.

### posix: os.fork, os.gethostname, os.getids, os.uptime

`os.fork`

  Invokes fork(2) and returns the result.

`os.gethostname`

  Invokes gethostname(3) and returns the result.

`os.getids`

  Returns the various user/group ids for the current process.

        . os.getids
        uid 1000 euid 1000 gid 100 egid 100

`os.uptime`

  Returns the number of seconds since system boot. See description of uptime in sysinfo(2).

## ANSI I/O (aio) and EVENTLOOP API

Jim provides an alternative object-based API for I/O.

See `open` and `socket` for commands which return an I/O handle.

### aio

`$handle accept ?addrvar?`

  Server socket only: Accept a connection and return stream. If `addrvar` is specified, the address of the connected client is stored in the named variable in the form addr:port for IP sockets or path for Unix domain sockets. See `socket` for details.

`$handle buffering none|line|full`

  Sets the buffering mode of the stream.

`$handle close ?r(ead)|w(rite)|-nodelete?`

  Closes the stream. The `read` and `write` arguments perform a "half-close" on a socket. See the shutdown(2) man page. The `-nodelete` option is applicable only for Unix domain sockets. It closes the socket but does not delete the bound path (e.g. after `os.fork`).

`$handle copyto tofd ?size?`

  Copy bytes to the file descriptor `tofd`. If `size` is specified, at most that many bytes will be copied. Otherwise copying continues until the end of the input file. Returns the number of bytes actually copied.

`$handle eof`

  Returns 1 if stream is at eof

`$handle filename`

  Returns the original filename associated with the handle. Handles returned by `socket` give the socket type instead of a filename.

`$handle flush`

  Flush the stream

`$handle gets ?var?`

  Read one line and return it or store it in the var

`$handle isatty`

  Returns 1 if the stream is a tty device.

`$handle lock ?-wait?`

  Apply a POSIX lock to the open file associated with the handle using fcntl(F_SETLK), or fcntl(F_SETLKW) to wait for the lock to be available if `-wait` is specified. The handle must be open for write access. Returns 1 if the lock was successfully obtained, 0 otherwise. An error occurs if the handle is not suitable for locking (e.g. if it is not open for write)

`$handle ndelay ?0|1?`

  Set O_NDELAY (if arg). Returns current/new setting. Note that in general ANSI I/O interacts badly with non-blocking I/O. Use with care.

`$handle peername`

  Returns the remote address or path of the connected socket. See getpeername(2).

`$handle puts ?-nonewline? str`

  Write the string, with newline unless -nonewline

`$handle read ?-nonewline? ?len?`

  Read and return bytes from the stream. To eof if no len.

`$handle recvfrom maxlen ?addrvar?`

  Receives a message from the handle via recvfrom(2) and returns it. At most `maxlen` bytes are read. If `addrvar` is specified, the sending address of the message is stored in the named variable in the form addr:port for IP sockets or path for Unix domain sockets. See `socket` for details.

`$handle seek offset ?start|current|end?`

  Seeks in the stream (default current)

`$handle sendto str ?address`

  Sends the string, `str`, to the given address (host:port or path) via the socket using sendto(2). This is intended for udp/dgram sockets and may give an error or behave in unintended ways for other handle types. Returns the number of bytes written.

`$handle sockname`

  Returns the bound address or path of the socket. See getsockname(2).

`$handle sockopt ?name value?`

  With no arguments, returns a dictionary of socket options currently set for the handle (will be empty for a non-socket). With `name` and `value`, sets the socket option to the given value. Currently supports the following boolean socket options: `broadcast, debug, keepalive, nosigpipe, oobinline, tcp_nodelay`, and the following integer socket options: `sndbuf, rcvbuf`

`$handle sync`

  Flush the stream, then fsync(2) to commit any changes to storage. Only available on platforms that support fsync(2).

`$handle tell`

  Returns the current seek position

`$handle tty ?settings?`

  If no arguments are given, returns a dictionary containing the tty settings for the stream. If arguments are given, they must either be a dictionary, or `setting value ...` Abbrevations are supported for both settings and values, so the following is acceptable: `$f tty parity e input c out raw`. Only available on platforms that support termios(3). Supported settings are:

  `baud rate`

    Baud rate. e.g. 115200

  `data 5|6|7|8`

    Number of data bits

  `stop 1|2`

    Number of stop bits

  `parity even|odd|none`

    Parity setting

  `handshake xonxoff|rtscts|none`

    Handshaking type

  `input raw|cooked`

    Input character processing. In raw mode, the usual key sequences such as ^C do not generate signals.

  `output raw|cooked`

    Output character processing. Typically CR → CRNL is disabled in raw mode.

  `echo 0|1`

    Disable or enable echo on input. Note that this is a set-only value. Setting `input` to `raw` or `cooked` will overwrite this setting.

  `vmin numchars`

    Minimum number of characters to read.

  `vtime time`

    Timeout for noncanonical read (units of 0.1 seconds)

`$handle ssl ?-server cert priv?`

  Upgrades the stream to a SSL/TLS session and returns the handle.

`$handle unlock`

  Release a POSIX lock previously acquired by `aio` `lock`.

`$handle verify`

  Verifies the certificate of a SSL/TLS stream peer

`load_ssl_certs dir`

  Loads SSL/TLS CA certificates for use during verification

### fconfigure

`fconfigure handle ?-blocking 0|1? ?-buffering noneline|full? ?-translation mode?`

  For compatibility with Tcl, a limited form of the `fconfigure` command is supported.

  - `fconfigure` `... -blocking` maps to `aio` `ndelay`

  - `fconfigure` `... -buffering` maps to `aio` `buffering`

  - `fconfigure` `... -translation` is accepted but ignored

### eventloop: after, vwait, update

The following commands allow a script to be invoked when the given condition occurs. If no script is given, returns the current script. If the given script is the empty, the handler is removed.

`$handle readable ?readable-script?`

  Sets or returns the script for when the socket is readable.

`$handle writable ?writable-script?`

  Sets or returns the script for when the socket is writable.

`$handle onexception ?exception-script?`

  Sets or returns the script for when oob data received.

For compatibility with Tcl, these may be prefixed with `fileevent`. e.g.

  `fileevent $handle readable ...`

Time-based execution is also available via the eventloop API.

`after ms`

  Sleeps for the given number of milliseconds. No events are processed during this time.

`after ms|idle script ?script ...?`

  The scripts are concatenated and executed after the given number of milliseconds have elapsed. If idle is specified, the script will run the next time the event loop is processed with `vwait` or `update`. The script is only run once and then removed. Returns an event id.

`after cancel id|command`

  Cancels an `after` event with the given event id or matching command (script). Returns the number of milliseconds remaining until the event would have fired. Returns the empty string if no matching event is found.

`after info ?id?`

  If `id` is not given, returns a list of current `after` events. If `id` is given, returns a list containing the associated script and either timer or idle to indicated the type of the event. An error occurs if `id` does not match an event.

`vwait variable`

  A call to `vwait` enters the eventloop. `vwait` processes events until the named (global) variable changes or all event handlers are removed. The variable need not exist beforehand. If there are no event handlers defined, `vwait` returns immediately.

`update ?idletasks?`

  A call to `update` enters the eventloop to process expired events, but no new events. If idletasks is specified, only expired time events are handled, not file events. Returns once handlers have been run for all expired events.

Scripts are executed at the global scope. If an error occurs during a handler script, an attempt is made to call (the user-defined command) `bgerror` with the details of the error. If the `bgerror` command does not exist, the error message details are printed to stderr instead.

If a file event handler script generates an error, the handler is automatically removed to prevent infinite errors. (A time event handler is always removed after execution).

`bgerror msg`

  Called when an event handler script generates an error. Note that the normal command resolution rules are used for bgerror. First the name is resolved in the current namespace, then in the global scope.

### socket

Various socket types may be created.

`socket unix path`

  A unix domain socket client connected to path

`socket unix.server path`

  A unix domain socket server listening on path

`socket unix.dgram ?path?`

  A unix domain socket datagram client, optionally connected to path

`socket unix.dgram.server path`

  A unix domain socket datagram server server listening on path

`socket ?-ipv6? stream addr:port`

  A TCP socket client. (See the forms for `addr` below)

`socket ?-ipv6? stream.server ?addr:?port`

  A TCP socket server (`addr` defaults to `0.0.0.0` for IPv4 or `[::]` for IPv6).

`socket ?-ipv6? dgram ?addr:port?`

  A UDP socket client. If the address is not specified, the client socket will be unbound and sendto must be used to indicated the destination.

`socket ?-ipv6? dgram.server addr:port`

  A UDP socket server.

`socket pipe`

  A synonym for `pipe`

`socket pair`

  A socketpair (see socketpair(2)). Like `pipe`, this command returns a list of two channels: {s1 s2}. These channels are both readable and writable.

This command creates a socket connected (client) or bound (server) to the given address.

The returned value is channel and may generally be used with the various file I/O commands (gets, puts, read, etc.), either as object-based syntax or Tcl-compatible syntax.

        . set f [socket stream www.google.com:80]
        aio.sockstream1
        . $f puts -nonewline "GET / HTTP/1.0\r\n\r\n"
        . $f gets
        HTTP/1.0 302 Found
        . $f close

Server sockets, however support only accept, which is most useful in conjunction with the EVENTLOOP API.

        set f [socket stream.server 80]
        $f readable {
            set client [$f accept]
            $client gets $buf
            ...
            $client puts -nonewline "HTTP/1.1 404 Not found\r\n"
            $client close
        }
        vwait done

The address, `addr`, can be given in one of the following forms:

1. For IPv4 socket types, an IPv4 address such as 192.168.1.1

2. For IPv6 socket types, an IPv6 address such as [fe80::1234] or [::]

3. A hostname

Note that on many systems, listening on an IPv6 address such as [::] will also accept requests via IPv4.

Where a hostname is specified, the `first` returned address is used which matches the socket type is used.

An unconnected dgram socket (either dgram or unix.dgram) must use `sendto` to specify the destination address.

The path for Unix domain sockets is automatically removed when the socket is closed. Use `close` `-nodelete` in the rare case where this behaviour should be avoided (e.g. after `os.fork`).

### syslog

`syslog ?options? ?priority? message`

This command sends message to system syslog facility with given priority. Valid priorities are:

    emerg, alert, crit, err, error, warning, notice, info, debug

If a message is specified, but no priority is specified, then a priority of info is used.

By default, facility user is used and the value of global tcl variable argv0 is used as ident string. However, any of the following options may be specified before priority to control these parameters:

`-facility value`

  Use specified facility instead of user. The following values for facility are recognized:

      authpriv, cron, daemon, kernel, lpr, mail, news, syslog, user,
      uucp, local0-local7

`-ident string`

  Use given string instead of argv0 variable for ident string.

`-options integer`

  Set syslog options such as `LOG_CONS`, `LOG_NDELAY`. You should use numeric values of those from your system syslog.h file, because I haven’t got time to implement yet another hash table.

### pack: pack, unpack

The optional pack extension provides commands to encode and decode binary strings.

`pack varName value -intle|-intbe|-floatle|-floatbe|-str bitwidth ?bitoffset?`

  Packs the binary representation of `value` into the variable `varName`. The value is packed according to the given type (integer/floating point/string, big-endian/little-endian), width and bit offset. The variable is created if necessary (like `append`). The variable is expanded if necessary.

`unpack binvalue -intbe|-intle|-uintbe|-uintle|-floatbe|-floatle|-str bitpos bitwidth`

  Unpacks bits from `binvalue` at bit position `bitpos` and with `bitwidth`. Interprets the value according to the type (integer/floating point/string, big-endian/little-endian and signed/unsigned) and returns it. For integer types, `bitwidth` may be up to the size of a Jim Tcl integer (typically 64 bits). For floating point types, `bitwidth` may be 32 bits (for single precision numbers) or 64 bits (for double precision). For the string type, both the width and the offset must be on a byte boundary (multiple of 8). Attempting to access outside the length of the value will return 0 for integer types, 0.0 for floating point types or the empty string for the string type.

### zlib

The optional zlib extension provides a Tcl-compatible subset of the `zlib` command.

`crc32 data ?startValue?`

  Returns the CRC32 checksum of a buffer. Optionally, an initial value may be specified; this is most useful for calculating the checksum of chunked data read from a stream (for instance, a pipe).

`deflate string ?level?`

  Compresses a buffer and outputs a raw, Deflate-compressed stream. Optionally, a compression level (1-9) may be specified to choose the desired speed vs. compression rate ratio.

`inflate data ?bufferSize?`

  Decompresses a raw, Deflate-compressed stream. When the uncompressed data size is known and specified, memory allocation is more efficient. Otherwise, decomperssion is chunked and therefore slower.

`gzip string ?-level level?`

  Compresses a buffer and adds a gzip header.

`gunzip data ?-buffersize size?`

  Decompresses a gzip-compressed buffer. Decompression is chunked, with a default, small buffer size of 64K which guarantees lower memory footprint at the cost of speed. It is recommended to use a bigger size, on systems without a severe memory constraint.

### binary

The optional, pure-Tcl binary extension provides the Tcl-compatible `binary` `scan` and `binary` `format` commands based on the low-level `pack` and `unpack` commands.

See the Tcl documentation at: http://www.tcl.tk/man/tcl8.5/TclCmd/binary.htm

Note that binary format with f/r/R specifiers (single-precision float) uses the value of Infinity in case of overflow.

### oo: class, super

The optional, pure-Tcl oo extension provides object-oriented (OO) support for Jim Tcl.

See the online documentation (http://jim.tcl.tk/index.html/doc/www/www/documentation/oo/) for more details.

`class classname ?baseclasses? classvars`

  Create a new class, `classname`, with the given dictionary (`classvars`) as class variables. These are the initial variables which all newly created objects of this class are initialised with. If a list of baseclasses is given, methods and instance variables are inherited.

`super method ?args ...?`

  From within a method, invokes the given method on the base class. Note that this will only call the last baseclass given.

### tree

The optional, pure-Tcl tree extension implements an OO, general purpose tree structure similar to that provided by tcllib ::struct::tree (http://core.tcl.tk/tcllib/doc/trunk/embedded/www/tcllib/files/modules/struct/struct_tree.html)

A tree is a collection of nodes, where each node (except the root node) has a single parent and zero or more child nodes (ordered), as well as zero or more attribute/value pairs.

`tree`

  Creates and returns a new tree object with a single node named "root". All operations on the tree are invoked through this object.

`$tree destroy`

  Destroy the tree and all it’s nodes. (Note that the tree will also be automatically garbage collected once it goes out of scope).

`$tree set nodename key value`

  Set the value for the given attribute key.

`$tree lappend nodename key value ...`

  Append to the (list) value(s) for the given attribute key, or set if not yet set.

`$tree keyexists nodename key`

  Returns 1 if the given attribute key exists.

`$tree get nodename key`

  Returns the value associated with the given attribute key.

`$tree getall nodename`

  Returns the entire attribute dictionary associated with the given key.

`$tree depth nodename`

  Returns the depth of the given node. The depth of "root" is 0.

`$tree parent nodename`

  Returns the node name of the parent node, or "" for the root node.

`$tree numchildren nodename`

  Returns the number of child nodes.

`$tree children nodename`

  Returns a list of the child nodes.

`$tree next nodename`

  Returns the next sibling node, or "" if none.

`$tree insert nodename ?index?`

  Add a new child node to the given node. The index is a list index such as `3` or `end-2`. The default index is `end`. Returns the name of the newly added node.

`$tree walk nodename dfs|bfs {actionvar nodevar} script`

  Walks the tree starting from the given node, either breadth first (`bfs`) depth first (`dfs`). The value `"enter"` or `"exit"` is stored in variable `actionvar`. The name of each node is stored in `nodevar`. The script is evaluated twice for each node, on entry and exit.

`$tree dump`

  Dumps the tree contents to stdout

### tcl::prefix

The optional tclprefix extension provides the Tcl8.6-compatible `tcl::prefix` command (http://www.tcl.tk/man/tcl8.6/TclCmd/prefix.htm) for matching strings against a table of possible values (typically commands or options).

`tcl::prefix all table string`

  Returns a list of all elements in `table` that begin with the prefix `string`.

`tcl::prefix longest table string`

  Returns the longest common prefix of all elements in `table` that begin with the prefix `string`.

`tcl::prefix match ?options? table string`

  If `string` equals one element in `table` or is a prefix to exactly one element, the matched element is returned. If not, the result depends on the `-error` option.

  - `-exact` Accept only exact matches.

  - `-message string` Use `string` in the error message at a mismatch. Default is "option".

  - `-error options` The options are used when no match is found. If `options` is empty, no error is generated and an empty string is returned. Otherwise the options are used as return options when generating the error message. The default corresponds to setting `-level 0`.

### tcl::autocomplete

Scriptable command line completion is supported in the interactive shell, jimsh, through the `tcl::autocomplete` callback. A simple implementation is provided, however this may be replaced with a custom command instead if desired.

In the interactive shell, press <TAB> to activate command line completion.

`tcl::autocomplete commandline`

  This command is called with the current command line when the user presses <TAB>. The command should return a list of all possible command lines that match the current command line. For example if `pr` is the current command line, the list `{prefix proc}` may be returned.

### history

The optional history extension provides script access to the command line editing and history support available in jimsh. See examples/jtclsh.tcl for an example. Note: if line editing support is not available, `history` `getline` acts like `gets` and the remaining subcommands do nothing.

`history load filename`

  Load history from a (text) file. If the file does not exist or is not readable, it is ignored.

`history getline prompt ?varname?`

  Displays the given prompt and allows a line to be entered. Similarly to `gets`, if `varname` is given, it receives the line and the length of the line is returned, or -1 on EOF. If `varname` is not given, the line is returned directly.

`history completion command`

  Sets an autocompletion command (see `tcl::autocomplete`) that is active during `history` `getline`. If the command is empty, autocompletion is disabled.

`history add line`

  Adds the given line to the history buffer.

`history save filename`

  Saves the current history buffer to the given file.

`history show`

  Displays the current history buffer to standard output.

### namespace

Provides namespace-related functions. See also: http://www.tcl.tk/man/tcl8.6/TclCmd/namespace.htm

`namespace code script`

  Captures the current namespace context for later execution of the script `script`. It returns a new script in which script has been wrapped in a `namespace inscope` command.

`namespace current`

  Returns the fully-qualified name for the current namespace.

`namespace delete ?namespace …?`

  Deletes all commands and variables with the given namespace prefixes.

`namespace eval namespace arg ?arg…?`

  Activates a namespace called `namespace` and evaluates some code in that context.

`namespace origin command`

  Returns the fully-qualified name of the original command to which the imported command `command` refers.

`namespace parent ?namespace?`

  Returns the fully-qualified name of the parent namespace for namespace `namespace`, if given, otherwise for the current namespace.

`namespace qualifiers string`

  Returns any leading namespace qualifiers for `string`

`namespace tail string`

  Returns the simple name at the end of a qualified string.

`namespace upvar namespace ?arg…?`

  This command arranges for zero or more local variables in the current procedure to refer to variables in `namespace`

`namespace which ?-command|-variable? name`

  Looks up `name` as either a command (the default) or variable and returns its fully-qualified name.

### interp

The optional interp command allows sub-interpreters to be created where commands may be run independently (but synchronously) of the main interpreter.

`interp`

  Creates and returns a new interpreter object (command). The created interpeter contains any built-in commands along with static extensions, but does not include any dynamically loaded commands (package require, load). These must be reloaded in the child interpreter if required.

`$interp delete`

  Deletes the interpeter object.

`$interp eval script …`

  Evaluates a script in the context for the child interpreter, in the same way as eval.

`$interp alias alias childcmd parentcmd ?arg …?`

  Similar to alias, but creates a command, `childcmd`, in the child interpreter that is an alias for `parentcmd` in the parent interpreter, with the given, fixed arguments. The alias may be deleted in the child with rename.

### json::encode

The Tcl → JSON encoder is part of the optional json package.

`json::encode value ?schema?`

  Encode a Tcl value as JSON according to the schema (defaults to `str`). The following schema types are supported:

  - str - Tcl string → JSON string

  - num - Tcl value → bare numeric value or null

  - bool - Tcl boolean value → true, false

  - obj ?name subschema …? - Tcl dict → JSON object. For each dict key matching name, the corresponding subschema is applied. The special name `*` matches any keys not otherwise matched, otherwise the default `str` is used.

  - list ?subschema? - Tcl list → JSON array. The subschema (default `str`) is applied for each element of the list/array.

  - mixed ?subschema …? = Tcl list → JSON array. Each subschema is applied for the corresponding element of the list/array.

  The following are examples:

        . json::encode {1 2 true false null 5.0} list
        [ "1", "2", "true", "false", "null", "5.0" ]
        . json::encode {1 2 true false null 5.0} {list num}
        [ 1, 2, true, false, null, 5.0 ]
        . json::encode {0 1 2 true false 5.0 off} {list bool}
        [ false, true, true, true, false, true, false ]
        . json::encode {a 1 b hello c {3 4}} obj
        { "a":"1", "b":"hello", "c":"3 4" }
        . json::encode {a 1 b hello c {3 4}} {obj a num c {list num}}
        { "a":1, "b":"hello", "c":[ 3, 4 ] }
        . json::encode {true true {abc def}} {mixed str num obj}
        [ "true", true, { "abc":"def" } ]
        . json::encode {a 1 b 3.0 c hello d null} {obj c str * num}
        { "a":1, "b":3.0, "c":"hello", "d":null }

### json::decode

The JSON → Tcl decoder is part of the optional json package.

`json::decode ?-index? ?-null string? ?-schema? json-string`

  Decodes the given JSON string (must be array or object) into a Tcl data structure. If `-index` is specified, decodes JSON arrays as dictionaries with numeric keys. This makes it possible to retrieve data from nested arrays and dictionaries with just `dict get`. With the option `-schema` returns a list of `{data schema}` where the schema is compatible with `json::encode`. Otherwise just returns the data. Decoding is as follows (with schema types listed in parentheses):

  - object → dict (obj)

  - array → list (mixed or list)

  - number → as-is (num)

  - boolean → as-is (bool)

  - string → string (str)

  - null → supplied null string or the default `"null"` (num)

  Note that an object decoded into a dict will return the keys in the same order as the original string.

        . json::decode {[1, 2]}
        {1 2}
        . json::decode -schema {[1, 2]}
        {1 2} {list num}
        . json::decode -schema {{"a":1, "b":2}}
        {a 1 b 2} {obj a num b num}
        . json::decode -schema {[1, 2, {a:"b", c:false}, "hello"]}
        {1 2 {a b c false} hello} {mixed num num {obj a str c bool} str}
        . json::decode -index {["foo", "bar"]}
        {0 foo 1 bar}

## BUILT-IN VARIABLES

The following global variables are created automatically by the Tcl library.

`env`

  This variable is set by Jim as an array whose elements are the environment variables for the process. Reading an element will return the value of the corresponding environment variable. This array is initialised at startup from the `env` command. It may be modified and will affect the environment passed to commands invoked with `exec`.

`platform_tcl`

  This variable is set by Jim as an array containing information about the platform on which Jim was built. Currently this includes os and platform.

`auto_path`

  This variable contains a list of paths to search for packages. It defaults to a location based on where jim is installed (e.g. `/usr/local/lib/jim`), but may be changed by `jimsh` or the embedding application. Note that `jimsh` will consider the environment variable `$JIMLIB` to be a list of colon-separated list of paths to add to `auto_path`.

`errorCode`

  This variable holds the value of the -errorcode return option set by the most recent error that occurred in this interpreter. This list value represents additional information about the error in a form that is easy to process with programs. The first element of the list identifies a general class of errors, and determines the format of the rest of the list. The following formats for -errorcode return options are used by the Tcl core; individual applications may define additional formats. Currently only `exec` sets this variable. Otherwise it will be `NONE`.

The following global variables are set by jimsh.

`tcl_interactive`

  This variable is set to 1 if jimsh is started in interactive mode or 0 otherwise.

`tcl_platform`

  This variable is set by Jim as an array containing information about the platform upon which Jim was built. The following is an example of the contents of this array.

        tcl_platform(byteOrder)     = littleEndian
        tcl_platform(engine)        = Jim
        tcl_platform(os)            = Darwin
        tcl_platform(platform)      = unix
        tcl_platform(pointerSize)   = 8
        tcl_platform(threaded)      = 0
        tcl_platform(wordSize)      = 8
        tcl_platform(pathSeparator) = :

`argv0`

  If jimsh is invoked to run a script, this variable contains the name of the script.

`argv`

  If jimsh is invoked to run a script, this variable contains a list of any arguments supplied to the script.

`argc`

  If jimsh is invoked to run a script, this variable contains the number of arguments supplied to the script.

`jim::argv0`

  The value of argv[0] when jimsh was invoked.

The following variables have special meaning to Jim Tcl:

`jim::defer`

  If this variable is set, it is considered to be a list of scripts to evaluate when the current proc exits (local variables), or the interpreter exits (global variable). See `defer`.

`history::multiline`

  If this variable is set to "1", interactive line editing operates in multiline mode. That is, long lines will wrap across multiple lines rather than scrolling within a single line.

## CHANGES IN PREVIOUS RELEASES

### In v0.74

1. Numbers with leading zeros are treated as decimal, not octal

2. Add `aio` `isatty`

3. Add LFS (64 bit) support for `aio` `seek`, `aio` `tell`, `aio` `copyto`, `file` `copy`

4. `string` `compare` and `string` `equal` now support -length

5. `glob` now supports -directory

### In v0.73

1. Built-in regexp now support non-capturing parentheses: (?:…)

2. Add `string` `replace`

3. Add `string` `totitle`

4. Add `info` `statics`

5. Add `build-jim-ext` for easy separate building of loadable modules (extensions)

6. `local` now works with any command, not just procs

7. Add `info` `alias` to access the target of an alias

8. UTF-8 encoding past the basic multilingual plane (BMP) is supported

9. Add `tcl::prefix`

10. Add `history`

11. Most extensions are now enabled by default

12. Add support for namespaces and the `namespace` command

13. Add `apply`

### In v0.72

1. procs now allow args and optional parameters in any position

2. Add Tcl-compatible expr functions, `rand()`, `srand()` and `pow()`

3. Add support for the -force option to `file` `delete`

4. Better diagnostics when `source` fails to load a script with a missing quote or bracket

5. New `tcl_platform(pathSeparator)`

6. Add support settings the modification time with `file` `mtime`

7. `exec` is now fully supported on win32 (mingw32)

8. `file` `join`, `pwd`, `glob` etc. now work for mingw32

9. Line editing is now supported for the win32 console (mingw32)

10. Add `aio` `listen` command

### In v0.71

1. Allow args to be renamed in procs

2. Add `$(…)` shorthand syntax for expressions

3. Add automatic reference variables in procs with `&var` syntax

4. Support `jimsh --version`

5. Additional variables in `tcl_platform()`

6. `local` procs now push existing commands and `upcall` can call them

7. Add `loop` command (TclX compatible)

8. Add `aio` `buffering` command

9. `info` `complete` can now return the missing character

10. `binary` `format` and `binary` `scan` are now (optionally) supported

11. Add `string` `byterange`

12. Built-in regexp now support non-greedy repetition (*?, +?, ??)

### In v0.70

1. `platform_tcl()` settings are now automatically determined

2. Add aio `$handle filename`

3. Add `info` `channels`

4. The bio extension is gone. Now `aio` supports copyto.

5. Add `exists` command

6. Add the pure-Tcl oo extension

7. The `exec` command now only uses vfork(), not fork()

8. Unit test framework is less verbose and more Tcl-compatible

9. Optional UTF-8 support

10. Optional built-in regexp engine for better Tcl compatibility and UTF-8 support

11. Command line editing in interactive mode, e.g. jimsh

### In v0.63

1. `source` now checks that a script is complete (.i.e. not missing a brace)

2. info complete now uses the real parser and so is 100% accurate

3. Better access to live stack frames with info frame, `stacktrace` and `stackdump`

4. `tailcall` no longer loses stack trace information

5. Add `alias` and `curry`

6. `lambda`, `alias` and `curry` are implemented via `tailcall` for efficiency

7. `local` allows procedures to be deleted automatically at the end of the current procedure

8. udp sockets are now supported for both clients and servers.

9. vfork-based exec is now working correctly

10. Add file tempfile

11. Add socket pipe

12. Enhance try … on … finally to be more Tcl 8.6 compatible

13. It is now possible to `return` from within `try`

14. IPv6 support is now included

15. Add string is

16. Event handlers works better if an error occurs. eof handler has been removed.

17. `exec` now sets $::errorCode, and catch sets opts(-errorcode) for exit status

18. Command pipelines via open "|…" are now supported

19. `pid` can now return pids of a command pipeline

20. Add info references

21. Add support for after `'ms`, 'after idle, after info, `update`

22. `exec` now sets environment based on $::env

23. Add dict keys

24. Add support for lsort -index

### In v0.62

1. Add support to `exec` for >&, >>&, |&, 2>@1

2. Fix `exec` error messages when special token (e.g. >) is the last token

3. Fix `subst` handling of backslash escapes.

4. Allow abbreviated options for `subst`

5. Add support for `return`, `break`, `continue` in subst

6. Many `expr` bug fixes

7. Add support for functions in `expr` (e.g. int(), abs()), and also in, ni list operations

8. The variable name argument to `regsub` is now optional

9. Add support for unset -nocomplain

10. Add support for list commands: `lassign`, `lrepeat`

11. Fully-functional `lsearch` is now implemented

12. Add info nameofexecutable and info returncodes

13. Allow `catch` to determine what return codes are caught

14. Allow `incr` to increment an unset variable by first setting to 0

15. Allow args and optional arguments to the left or required arguments in `proc`

16. Add file copy

17. Add try … finally command

## LICENCE

    Copyright 2005 Salvatore Sanfilippo <antirez@invece.org>
    Copyright 2005 Clemens Hintze <c.hintze@gmx.net>
    Copyright 2005 patthoyts - Pat Thoyts <patthoyts@users.sf.net>
    Copyright 2008 oharboe - Oyvind Harboe - oyvind.harboe@zylin.com
    Copyright 2008 Andrew Lunn <andrew@lunn.ch>
    Copyright 2008 Duane Ellis <openocd@duaneellis.com>
    Copyright 2008 Uwe Klein <uklein@klein-messgeraete.de>
    Copyright 2009 Steve Bennett <steveb@workware.net.au>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above
       copyright notice, this list of conditions and the following
       disclaimer in the documentation and/or other materials
       provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE JIM TCL PROJECT ``AS IS'' AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
    THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    JIM TCL PROJECT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
    INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
    (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
    STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
    ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    The views and conclusions contained in the software and documentation
    are those of the authors and should not be interpreted as representing
    official policies, either expressed or implied, of the Jim Tcl Project.