GETOPT(1) | General Commands Manual | GETOPT(1) |
getopt
— parse
command options
args=`getopt optstring
$*` |
; errcode=$?; set -- $args |
The getopt
utility 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 white space. The special option
‘--
’ is used to delimit the end of the
options. The getopt
utility 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 getopt
utility prints an error message
on the standard error output and exits with status > 0 when it encounters
an option letter not included in optstring.
The following code fragment shows how one might process the
arguments for a command that can take the options -a
and -b
, and the option -o
,
which requires an argument.
args=`getopt abo: $*` # you should not use `getopt abo: "$@"` since that would parse # the arguments differently from what the set command below does. if [ $? -ne 0 ]; then echo 'Usage: ...' exit 2 fi set -- $args # You cannot use the set command with a backquoted getopt directly, # since the exit code from getopt would be shadowed by those of set, # which is zero by definition. while :; do case "$1" in -a|-b) echo "flag $1 set"; sflags="${1#-}$sflags" shift ;; -o) echo "oarg is '$2'"; oarg="$2" shift; shift ;; --) shift; break ;; esac done echo "single-char flags: '$sflags'" echo "oarg is '$oarg'"
This code will accept any of the following as equivalent:
cmd -aoarg file1 file2 cmd -a -o arg file1 file2 cmd -oarg -a file1 file2 cmd -a -oarg -- file1 file2
Written by Henry Spencer, working from a Bell Labs manual page. Behavior believed identical to the Bell version. Example changed in FreeBSD version 3.2 and 4.0.
Whatever getopt(3) has.
Arguments containing white space or embedded shell metacharacters
generally will not survive intact; this looks easy to fix but is not. People
trying to fix getopt
or the example in this manpage
should check the history of this file in
FreeBSD.
The error message for an invalid option is identified as coming
from 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.
Each shellscript has to carry complex code to parse arguments halfway correctly (like the example presented here). A better getopt-like tool would move much of the complexity into the tool and keep the client shell scripts simpler.
August 1, 2015 | macOS 14.6 |