parse command options
getopt is used to break up options in
command lines for easy parsing by shell procedures, and to check for legal
options. optstring 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.
getopt will place
‘--’ in the arguments at the end of the options, or recognize
it if used explicitly. The shell arguments ($1,
$2, ...) are 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
-b, and the option
which requires an argument.
args=`getopt abo: $*` if [ $? -ne 0 ] then echo 'Usage: ...' exit 2 fi set -- $args while [ $# -ne 0 ] do case "$1" in -a|-b) flag="$1"; shift;; -o) oarg="$2"; shift; shift;; --) shift; break;; esac done
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
getopt 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
will prevent the exit value from
getopt from being
Whatever getopt(3) has.
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
getopt rather than from the shell procedure
containing the invocation of
getopt; this 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.