---

10.69.41 getopt ¶

POSIX specification:
https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html

LSB specification:
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/libutil-getopt-3.html

Gnulib module: getopt-posix or getopt-gnu

The module getopt-gnu has support for “long options” and for “options that take optional arguments”. Compared to the API defined by POSIX, it adds a header file <getopt.h> and a function getopt_long.

Portability problems fixed by either Gnulib module getopt-posix or getopt-gnu:

• This function is missing on some platforms: MSVC 14.
• The value of optind after a missing required argument is wrong on some platforms: macOS 14, AIX 7.1, mingw.

Portability problems fixed by Gnulib module getopt-gnu:

• The function getopt does not support the ‘+’ flag in the options string on some platforms: macOS 14, AIX 5.2, HP-UX 11, Solaris 11 2010-11.
• The function getopt does not obey the combination of ‘+’ and ‘:’ flags in the options string on some platforms: glibc 2.11.
• The function getopt does not obey the ‘-’ flag in the options string when POSIXLY_CORRECT is set on some platforms: Cygwin 1.7.0.
• The function getopt does not support options with optional arguments on some platforms: macOS 14, OpenBSD 4.0, AIX 5.2, HP-UX 11, Solaris 11 2010-11, Cygwin 1.5.x.
• The function getopt_long is missing on some platforms: AIX 5.1, HP-UX 11, Solaris 9, MSVC 14.
• The function getopt_long does not support abbreviated long options where all disambiguations are equivalent on some platforms: OpenBSD 5.0.
• The function getopt_long_only is missing on some platforms: FreeBSD 5.2.1, NetBSD 10.0, AIX 5.1, HP-UX 11, Solaris 9, mingw, MSVC 14.
• This function crashes if the option string includes W; on some platforms: glibc 2.14.

Portability problems not fixed by Gnulib:

• The default behavior of the glibc implementation of getopt allows mixing option and non-option arguments on the command line in any order. Other implementations, such as the one in Cygwin, enforce strict POSIX compliance: they require that the option arguments precede the non-option arguments. This is something to watch out in your program’s testsuite.
• The glibc implementation allows a complete reset of the environment, including re-checking for POSIXLY_CORRECT, by setting optind to 0. Several BSD implementations provide optreset, causing a reset by setting it non-zero, although it does not necessarily re-read POSIXLY_CORRECT. Solaris getopt does not support either reset method, but does not maintain state that needs the extra level of reset.
• On some platforms, this function does not set the stream error indicator on attempts to write to a read-only stream: glibc 2.13, Cygwin 1.7.9.