getopt Man page

GETOPT(1) User Commands GETOPT(1)

NAME

getopt – parse command options (enhanced)

SYNOPSIS

getopt optstring parameters
getopt [options] [–] optstring parameters
getopt [options] -o|–options optstring [options] [–] parameters

DESCRIPTION

getopt is used to break up (parse) options in command lines for easy
parsing by shell procedures, and to check for legal options. It uses
the GNU getopt routines to do this.

The parameters getopt is called with can be divided into two parts:
options which modify the way getopt will do the parsing (the options
and the optstring in the SYNOPSIS), and the parameters which are to be
parsed (parameters in the SYNOPSIS). The second part will start at the
first non-option parameter that is not an option argument, or after the
first occurrence of ‘–‘. If no ‘-o’ or ‘–options’ option is found in
the first part, the first parameter of the second part is used as the
short options string.

If the environment variable GETOPT_COMPATIBLE is set, or if the first
parameter is not an option (does not start with a ‘-‘, the first format
in the SYNOPSIS), getopt will generate output that is compatible with
that of other versions of getopt. It will still do parameter shuf‐
fling and recognize optional arguments (see section COMPATIBILITY for
more information).

Traditional implementations of getopt are unable to cope with white‐
space and other (shell-specific) special characters in arguments and
non-option parameters. To solve this problem, this implementation can
generate quoted output which must once again be interpreted by the
shell (usually by using the eval command). This has the effect of pre‐
serving those characters, but you must call getopt in a way that is no
longer compatible with other versions (the second or third format in
the SYNOPSIS). To determine whether this enhanced version of getopt
is installed, a special test option (-T) can be used.

OPTIONS

-a, –alternative
Allow long options to start with a single ‘-‘.

-h, –help
Display help text and exit. No other output is generated.

-l, –longoptions longopts
The long (multi-character) options to be recognized. More than
one option name may be specified at once, by separating the
names with commas. This option may be given more than once, the
longopts are cumulative. Each long option name in longopts may
be followed by one colon to indicate it has a required argument,
and by two colons to indicate it has an optional argument.

-n, –name progname
The name that will be used by the getopt routines when it
reports errors. Note that errors of getopt are still
reported as coming from getopt.

-o, –options shortopts
The short (one-character) options to be recognized. If this
option is not found, the first parameter of getopt that does not
start with a ‘-‘ (and is not an option argument) is used as the
short options string. Each short option character in shortopts
may be followed by one colon to indicate it has a required argu‐
ment, and by two colons to indicate it has an optional argument.
The first character of shortopts may be ‘+’ or ‘-‘ to influence
the way options are parsed and output is generated (see section
SCANNING MODES for details).

-q, –quiet
Disable error reporting by getopt.

-Q, –quiet-output
Do not generate normal output. Errors are still reported by
getopt, unless you also use -q.

-s, –shell shell
Set quoting conventions to those of shell. If the -s option is
not given, the BASH conventions are used. Valid arguments are
currently ‘sh’ ‘bash’, ‘csh’, and ‘tcsh’.

-T, –test
Test if your getopt is this enhanced version or an old ver‐
sion. This generates no output, and sets the error status to 4.
Other implementations of getopt, and this version if the
environment variable GETOPT_COMPATIBLE is set, will return ‘–‘
and error status 0.

-u, –unquoted
Do not quote the output. Note that whitespace and special
(shell-dependent) characters can cause havoc in this mode (like
they do with other getopt implementations).

-V, –version
Display version information and exit. No other output is gener‐
ated.

PARSING
This section specifies the format of the second part of the parameters
of getopt (the parameters in the SYNOPSIS). The next section (OUTPUT)
describes the output that is generated. These parameters were typi‐
cally the parameters a shell function was called with. Care must be
taken that each parameter the shell function was called with corre‐
sponds to exactly one parameter in the parameter list of getopt (see
the EXAMPLES). All parsing is done by the GNU getopt routines.

The parameters are parsed from left to right. Each parameter is clas‐
sified as a short option, a long option, an argument to an option, or a
non-option parameter.

A simple short option is a ‘-‘ followed by a short option character.
If the option has a required argument, it may be written directly after
the option character or as the next parameter (i.e. separated by white‐
space on the command line). If the option has an optional argument, it
must be written directly after the option character if present.

It is possible to specify several short options after one ‘-‘, as long
as all (except possibly the last) do not have required or optional
arguments.

A long option normally begins with ‘–‘ followed by the long option
name. If the option has a required argument, it may be written
directly after the long option name, separated by ‘=’, or as the next
argument (i.e. separated by whitespace on the command line). If the
option has an optional argument, it must be written directly after the
long option name, separated by ‘=’, if present (if you add the ‘=’ but
nothing behind it, it is interpreted as if no argument was present;
this is a slight bug, see the BUGS). Long options may be abbreviated,
as long as the abbreviation is not ambiguous.

Each parameter not starting with a ‘-‘, and not a required argument of
a previous option, is a non-option parameter. Each parameter after a
‘–‘ parameter is always interpreted as a non-option parameter. If the
environment variable POSIXLY_CORRECT is set, or if the short option
string started with a ‘+’, all remaining parameters are interpreted as
non-option parameters as soon as the first non-option parameter is
found.

OUTPUT
Output is generated for each element described in the previous section.
Output is done in the same order as the elements are specified in the
input, except for non-option parameters. Output can be done in compat‐
ible (unquoted) mode, or in such way that whitespace and other special
characters within arguments and non-option parameters are preserved
(see QUOTING). When the output is processed in the shell script, it
will seem to be composed of distinct elements that can be processed one
by one (by using the shift command in most shell languages). This is
imperfect in unquoted mode, as elements can be split at unexpected
places if they contain whitespace or special characters.

If there are problems parsing the parameters, for example because a
required argument is not found or an option is not recognized, an error
will be reported on stderr, there will be no output for the offending
element, and a non-zero error status is returned.

For a short option, a single ‘-‘ and the option character are generated
as one parameter. If the option has an argument, the next parameter
will be the argument. If the option takes an optional argument, but
none was found, the next parameter will be generated but be empty in
quoting mode, but no second parameter will be generated in unquoted
(compatible) mode. Note that many other getopt implementations do
not support optional arguments.

If several short options were specified after a single ‘-‘, each will
be present in the output as a separate parameter.

For a long option, ‘–‘ and the full option name are generated as one
parameter. This is done regardless whether the option was abbreviated
or specified with a single ‘-‘ in the input. Arguments are handled as
with short options.

Normally, no non-option parameters output is generated until all
options and their arguments have been generated. Then ‘–‘ is gener‐
ated as a single parameter, and after it the non-option parameters in
the order they were found, each as a separate parameter. Only if the
first character of the short options string was a ‘-‘, non-option
parameter output is generated at the place they are found in the input
(this is not supported if the first format of the SYNOPSIS is used; in
that case all preceding occurrences of ‘-‘ and ‘+’ are ignored).

QUOTING

In compatible mode, whitespace or ‘special’ characters in arguments or
non-option parameters are not handled correctly. As the output is fed
to the shell script, the script does not know how it is supposed to
break the output into separate parameters. To circumvent this problem,
this implementation offers quoting. The idea is that output is gener‐
ated with quotes around each parameter. When this output is once again
fed to the shell (usually by a shell eval command), it is split cor‐
rectly into separate parameters.

Quoting is not enabled if the environment variable GETOPT_COMPATIBLE is
set, if the first form of the SYNOPSIS is used, or if the option ‘-u’
is found.

Different shells use different quoting conventions. You can use the
‘-s’ option to select the shell you are using. The following shells
are currently supported: ‘sh’, ‘bash’, ‘csh’ and ‘tcsh’. Actually,
only two ‘flavors’ are distinguished: sh-like quoting conventions and
csh-like quoting conventions. Chances are that if you use another
shell script language, one of these flavors can still be used.

SCANNING MODES
The first character of the short options string may be a ‘-‘ or a ‘+’
to indicate a special scanning mode. If the first calling form in the
SYNOPSIS is used they are ignored; the environment variable
POSIXLY_CORRECT is still examined, though.

If the first character is ‘+’, or if the environment variable
POSIXLY_CORRECT is set, parsing stops as soon as the first non-option
parameter (i.e. a parameter that does not start with a ‘-‘) is found
that is not an option argument. The remaining parameters are all
interpreted as non-option parameters.

If the first character is a ‘-‘, non-option parameters are outputted at
the place where they are found; in normal operation, they are all col‐
lected at the end of output after a ‘–‘ parameter has been generated.
Note that this ‘–‘ parameter is still generated, but it will always be
the last parameter in this mode.

COMPATIBILITY
This version of getopt is written to be as compatible as possible to
other versions. Usually you can just replace them with this version
without any modifications, and with some advantages.

If the first character of the first parameter of getopt is not a ‘-‘,
getopt goes into compatibility mode. It will interpret its first
parameter as the string of short options, and all other arguments will
be parsed. It will still do parameter shuffling (i.e. all non-option
parameters are output at the end), unless the environment variable
POSIXLY_CORRECT is set.

The environment variable GETOPT_COMPATIBLE forces getopt into compati‐
bility mode. Setting both this environment variable and POSIXLY_COR‐
RECT offers 100% compatibility for ‘difficult’ programs. Usually,
though, neither is needed.

In compatibility mode, leading ‘-‘ and ‘+’ characters in the short
options string are ignored.

RETURN CODES
getopt returns error code 0 for successful parsing, 1 if getopt
returns errors, 2 if it does not understand its own parameters, 3 if an
internal error occurs like out-of-memory, and 4 if it is called with
-T.

EXAMPLES
Example scripts for (ba)sh and (t)csh are provided with the getopt
distribution, and are optionally installed in /usr/share/getopt/ or
/usr/share/doc/ in the util-linux subdirectory.

ENVIRONMENT
POSIXLY_CORRECT
This environment variable is examined by the getopt routines.
If it is set, parsing stops as soon as a parameter is found that
is not an option or an option argument. All remaining parame‐
ters are also interpreted as non-option parameters, regardless
whether they start with a ‘-‘.

GETOPT_COMPATIBLE
Forces getopt to use the first calling format as specified in
the SYNOPSIS.

BUGS

getopt can parse long options with optional arguments that are given
an empty optional argument (but can not do this for short options).
This getopt treats optional arguments that are empty as if they were
not present.

The syntax if you do not want any short option variables at all is not
very intuitive (you have to set them explicitly to the empty string).

AUTHOR

Frodo Looijaard ⟨frodo@frodo.looijaard.name⟩

SEE ALSO

getopt, bash, tcsh.

AVAILABILITY
The getopt command is part of the util-linux package and is available
from Linux Kernel Archive ⟨ftp://ftp.kernel.org/pub/linux/utils/util-
linux/⟩.

util-linux December 2014 GETOPT(1)