parse command options
is used to break up options in command
lines for easy parsing by shell procedures, and to check for legal options.
is a string of recognized option
letters (see getopt(3)
); if a
letter is followed by a colon, the option is expected to have an argument
which may or may not be separated from it by whitespace. However, if a letter
is followed by two colons, the argument is optional and may not be separated
by whitespace - this is an extension not covered by POSIX. The special option
‘--’ is used to delimit the end of the options.
will place ‘--’ in the
arguments at the end of the options, or recognize it if used explicitly. The
shell arguments ($1
reset so that each option is preceded by a ‘-’ and in its own
shell argument; each option argument is also in its own shell argument.
The following code fragment shows how one might process the arguments for a
command that can take the options
, and the option
, which requires an argument.
args=`getopt abo: $*`
if [ $? -ne 0 ]
echo 'Usage: ...'
set -- $args
while [ $# -ne 0 ]
oarg="$2"; shift; shift;;
This code will accept any of the following as equivalent:
cmd -aoarg file file
cmd -a -o arg file file
cmd -oarg -a file file
cmd -a -oarg -- file file
prints an error message on the
standard error output when it encounters an option letter not included in
Written by Henry Spencer, working from a Bell Labs manual page. Behavior
believed identical to the Bell version.
Note that the construction
set -- `getopt optstring
is not recommended, as the exit value from set
prevent the exit value from
Arguments containing whitespace or embedded shell metacharacters generally will
not survive intact; this looks easy to fix but isn't.
The error message for an invalid option is identified as coming from
rather than from the shell procedure
containing the invocation of
again is hard to fix.
The precise best way to use the set
command to set
the arguments without disrupting the value(s) of shell options varies from one
shell version to another.