Updated: May 31, 1997
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getopt - parse command options (enhanced)
is used to break up
options in command lines for easy parsing by
shell procedures, and to check for legal options.
It uses the
routines to do this.
is called with can be divided into two parts: options
which modify the way getopt will parse
and the parameters which are to be
The second part will start at the first non-option parameter
that is not an option argument, or after the first occurrence of
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
is set, or if its first parameter
is not an option (does not start with a
this is the first format in the
will generate output that is compatible with that of other versions of
It will still do parameter shuffling and recognize optional
arguments (see section
for more information).
Traditional implementations of
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
command). This has the effect of preserving those characters, but
you must call
in a way that is no longer compatible with other versions (the second
or third format in the
To determine whether this enhanced version of
is installed, a special test option
can be used.
- -a, --alternative
Allow long options to start with a single
- -h, --help
Output a small usage guide and exit successfully. 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
Each long option name
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
routines when it reports errors. Note that errors of
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
that does not start with
(and is not an option argument) is used as the short options string.
Each short option character
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
to influence the way
options are parsed and output is generated (see section
- -q, --quiet
Disable error reporting by getopt(3).
- -Q, --quiet-output
Do not generate normal output. Errors are still reported by
unless you also use
- -s, --shell shell
Set quoting conventions to those of shell. If no -s argument is found,
conventions are used. Valid arguments are currently
- -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
- -T, --test
Test if your
is this enhanced version or an old version. This generates no output,
and sets the error status to 4. Other implementations of
and this version if the environment variable
and error status 0.
- -V, --version
Output version information and exit successfully. No other output is generated.
This section specifies the format of the second part of the parameters of
The next section
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
All parsing is done by the GNU
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 (ie. 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
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 (ie. 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
Long options may be abbreviated, as long as the abbreviation is not
Each parameter not starting with a
and not a required argument of
a previous option, is a non-option parameter. Each parameter after
parameter is always interpreted as a non-option parameter.
If the environment variable
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
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
mode, or in such way that whitespace and other special characters within
arguments and non-option parameters are preserved (see
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
but no second parameter will be generated in unquoted (compatible) mode.
Note that many other
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
is used; in that case all preceding occurrences of
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
command), it is split correctly into separate parameters.
Quoting is not enabled if the environment variable
is set, if the first form of the
is used, or if the option
Different shells use different quoting conventions. You can use the
option to select the shell you are using. The following shells are
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
to indicate a special scanning mode. If the first calling form
is used they are ignored; the environment variable
is still examined, though.
If the first character is
or if the environment variable
is set, parsing stops as soon as the first non-option parameter
(ie. a parameter that does not start with a
is found that
is not an option argument. The remaining parameters are all interpreted as
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 version of
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 (ie. all non-option parameters are outputted
at the end), unless the environment variable
The environment variable
into compatibility mode. Setting both this environment variable and
offers 100% compatibility for `difficult' programs. Usually, though,
neither is needed.
In compatibility mode, leading
characters in the short options string are ignored.
returns error code
for successful parsing,
if it does not understand its own parameters,
if an internal error occurs like out-of-memory, and
if it is called with
Example scripts for (ba)sh and (t)csh are provided with the
distribution, and are optionally installed in
This environment variable is examined by the
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
to use the first calling format as specified in the
can parse long options with optional arguments that are given an empty optional
argument (but can not do this for short options). This
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
Frodo Looijaard <email@example.com>
The getopt command is part of the util-linux-ng package and is available from
- SCANNING MODES
- RETURN CODES
- SEE ALSO
This document was created by
using the manual pages.