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getopt — parse command options (enhanced)
getopt [options]
[−−] optstring
parameters
getopt [options]
−o | −−options optstring [options]
[−−] parameters
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(3) 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(1). It will still do
parameter shuffling and recognize optional arguments (see
section COMPATIBILITY for more
information).
Traditional implementations of getopt(1) are unable to
cope with whitespace 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 preserving 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(1) is installed, a
special test option (−T)
can be used.
−a,
−−alternativeAllow long options to start with a single '−'.
−h,
−−helpDisplay help text and exit. No other output is generated.
−l,
−−longoptions longoptsThe 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 prognameThe name that will be used by the getopt(3) routines when it reports errors. Note that errors of getopt(1) are still reported as coming from getopt.
−o,
−−options shortoptsThe 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 argument,
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,
−−quietDisable error reporting by getopt(3).
−Q,
−−quiet−outputDo not generate normal output. Errors are still
reported by getopt(3), unless you
also use −q.
−s,
−−shell shellSet 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'.
−u,
−−unquotedDo not quote the output. Note that whitespace and special (shell−dependent) characters can cause havoc in this mode (like they do with other getopt(1) implementations).
−T,
−−testTest if your getopt(1) is this
enhanced version or an old version. This generates no
output, and sets the error status to 4. Other
implementations of getopt(1), and this
version if the environment variable GETOPT_COMPATIBLE is set, will return
'−−' and error
status 0.
−V,
−−versionDisplay version information and exit. No other output is generated.
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 typically the parameters a
shell function was called with. Care must be taken that each
parameter the shell function was called with corresponds to
exactly one parameter in the parameter list of getopt (see the
EXAMPLES). All parsing is done
by the GNU getopt(3) routines.
The parameters are parsed from left to right. Each parameter is classified 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 whitespace 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 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
compatible
(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(1) 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 generated 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).
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 generated with quotes around each parameter. When this output is once again fed to the shell (usually by a shell eval command), it is split correctly 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.
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 collected 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.
This version of getopt(1) 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 compatibility
mode. Setting both this environment variable and POSIXLY_CORRECT offers 100% compatibility
for 'difficult' programs. Usually, though, neither is
needed.
In compatibility mode, leading '−' and '+' characters in the short options string
are ignored.
getopt
returns error code 0 for
successful parsing, 1 if
getopt(3) 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.
Example scripts for (ba)sh and (t)csh are provided with
the getopt(1) distribution, and
are optionally installed in /usr/share/getopt/ or /usr/share/docs/ in the util-linux
subdirectory.
POSIXLY_CORRECTThis environment variable is examined by the getopt(3) 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 parameters are also interpreted as non−option parameters, regardless whether they start with a '−'.
GETOPT_COMPATIBLEForces getopt to use the
first calling format as specified in the SYNOPSIS.
getopt(3) can parse long options with optional arguments that are given an empty optional argument (but can not do this for short options). This getopt(1) 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).
The getopt command is part of the util-linux package and is available from Linux Kernel Archive
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