@node unsetenv
@subsection @code{unsetenv}
@findex unsetenv

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/unsetenv.html}

Gnulib module: unsetenv
@mindex unsetenv

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
AIX 5.1, HP-UX 11.23, Solaris 9, mingw, MSVC 14.
@item
This function has the return type @samp{void} instead of @samp{int} on some
platforms:
FreeBSD 6.0, NetBSD 1.6, OpenBSD 3.8.
@item
On some platforms, this function does not fail with @samp{EINVAL} when
passed an empty string or a string containing @samp{=}:
FreeBSD 6.0, NetBSD 1.6, OpenBSD 4.7.
@item
This function removes only the first value association for the given
environment variable, not all of them, on some platforms:
Solaris 11.4, Haiku.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
Older versions of POSIX required that @code{unsetenv(NULL)} gracefully
fail with @code{EINVAL}, but not all implementations guarantee this,
and the requirement was removed.
@end itemize
