getopt
parse command options (enhanced)
see also :
bash
Synopsis
getopt
optstring parameters
getopt [options] [--]
optstring parameters
getopt [options]
-o|--options
optstring [options] [--]
parameters
add an example, a script, a trick and tips
examples
Example scripts for (ba)sh and (t)csh are provided with the
getopt(1) distribution, and are optionally installed in
/usr/share/doc/util-linux/examples.
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(3)
routines to do this.
The parameters
getopt is called with can be divided into two parts:
options which modify the way getopt will parse
(options and
-o|--options
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
its first parameter is not an option (does not start with a
’-’, this is 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.
options
-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 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(3) routines when it reports errors. Note
that errors of getopt(1) 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 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,
--quiet
Disable error reporting by
getopt(3).
-Q,
--quiet-output
Do not generate normal output.
Errors are still reported by getopt(3), unless you
also use -q.
-s,
--shell shell
Set quoting conventions to
those of shell. If no -s argument is found, the
BASH conventions are used. Valid arguments
are currently ’sh’
’bash’, ’csh’, and
’tcsh’.
-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(1) implementations).
-T,
--test
Test 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,
--version
Output version information and
exit successfully. No other output is generated.
availability
The getopt command is part of the util-linux package and is
available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
compatibility
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 (ie. all non-option parameters are outputted 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.
environment
POSIXLY_CORRECT
This 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_COMPATIBLE
Forces getopt to use the first calling format as specified
in the SYNOPSIS.
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 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).
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 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 (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 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 (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 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.
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 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.
return codes
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.
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 (ie. 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.
bugs
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).
see also
getopt,
bash , tcsh.
author
Frodo Looijaard
<frodo[:at:]frodo.looijaard[:dot:]name>