Command line arguments in bash scripts
This is something that has always annoyed me about bash scripts… The fact that it’s difficult to run
/path/to/script.sh --foo=bar -v -n 10 blah -one='last arg'
So I decided to write up a bash function that let me easily (once the function was complete) access this type of information. And because I like sharing, here it is:
#!/bin/bash
function getopt() {
var=""
wantarg=0
for (( i=1; i< =$#; i+=1 )); do
lastvar=$var
var=${!i}
if [ "$var" = "" ]; then
continue
fi
echo \ $var | grep -q -- '='
if [ $? -eq 0 ]; then
## -*param=value
var=$(echo \ $var | sed -r s/'^[ ]*-*'/''/)
myvar=${var%=*}
myval=${var#*=}
eval "${myvar}"="'$myval'"
else
echo \ $var | grep -E -q -- '^[ ]*-'
if [ $? -eq 0 ]; then
# -*param$
var=$(echo \ $var | sed -r s/'^[ ]*-*'/''/)
eval "${var}"=1
wantarg=1
else
echo \ $var | grep -E -- '^[ ]*-'
if [ $? -eq 0 ]; then
# the current one has a dash, so cannot be
# the argument to the last parameter
wantarg=0
fi
if [ $wantarg -eq 1 ]; then
# parameter argument
val=$var
var=$lastvar
eval "${var}"="'${val}'"
wantarg=0
else
# parameter
if [ "${!var}" = "" ]; then
eval "${var}"=1
fi
wantarg=0
fi
fi
fi
done
}
OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS
now at this point (assuming the above command line parameter and script) I should have access to the following variables: $foo (”bar”) $v (1) $n (10) $blah (1) $one (”last arg”), like so:
OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS echo -e " foo:\t$foo v:\t$v n:\t$n blah:\t$blah one:\t$one "
You might be curious about this line:
OIFS=$IFS; IFS=$(echo -e "\n"); getopt $@; IFS=$OIFS
IFS is the variable that tells bash how strings are separated (and mastering its use will go a long way towards enhancing your bash scripting skills.) Anyhow, by default IFS=” ” which normally is OK, but in our case we dont want “last arg” to be two seperate strings, but one. I cannot put the IFS assignment inside the function because by that point bash has already split the variable, it needs to be done at a level of the script in which $@ has not been touched yet. So I store the current IFS variable in $OIFS (Old IFS) and set IFS to a newline character. After running the function we reassign IFS to what it was beforehand. This is because I dont know what you might be doing with your IFS. There are lots of reasons you might have already assigned it to something else, and I wouldnt want to break your flow. So we do the polite thing.
And in case the above gets munged for some reason you can see the plain text version here: bash-getopt/getopt.sh
Anyways, hope this helps someone out. If not it’s still here for me when *I* need it 
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9 People have left comments on this post
Hi there, thanks for the snippet. I use it for a shell script but I found a error / shortcomming:
run.sh --file "foobar" --arguments "--foo"
This will fail with “line XY: foo: command not found”, where XY points to the line:
eval “${var}”=1
(i.e. the first occurence of that, i.e. after var=$(echo \ $var | sed -r s/’^[ ]*-*’/”/) )
Could you possibly fix this?
PS: You might want to setup a GeSHi plugin for wordpress, that way your script will get highlighted properly. If not - drop me a mail, I’m a developer there
Thank you!
Bash has a built in function called getopts which does help with parsing command line arguement (help getopts for more info), but your solution seems to be a heck of a lot easier to use.
Thanks for sharing!
-Jeremy
Two comments:
1. Instead of
OIFS=$IFS; IFS=$(echo -e “\n”); getopt $@; IFS=$OIFS
you could also just write
getopt “$@”
2. It may be a security problem if the getopt function may write any variable in the normal namespace of the script. So, it’s better to prefix each variable by e.g. “arg_”. So –name bothie won’t get name=”bothie” but arg_name=”bothie”.
Regards, Bodo
Oh, and another thing.
@Milian Wolff:
It doesn’t make a difference if you write
run.sh –file “foobar” –arguments “–foo”
or if you write
run.sh –file “foobar” –arguments –foo
For this reason the script should be updates to allow for arguments like “–arguments=–foo”
Regards, Bodo
>>> For this reason the script should be updates to allow for arguments like “–arguments=–foo”
Watching closer on the script I discovered, that the script already support that style of arguments.
However, it doesn’t support other things. Imagine
mv -i oldname newname
This would lead to i=oldname and newname -> ???
In short: This script helps in parsing command line options, but it isn’t the non-plus-ultra yet.
Regards, Bodo
This is a pretty retarded and feature-lacking re-invention of the wheel. Seriously:
help getopt;
It’s a bash built-in (and mostly compatible binaries that the built-in was based off of exist on any sane system even without bash!).
Example usage:
# Parse commandline options.
GETOPT=”$(getopt -o c:olhdfs –long children:,stdout,syslog,help,dry-run,force,status -n “$0″ — “$@”)”
if [ "$?" -gt '0' ]; then
echo “$USAGE”
exit 1
fi
eval set — “$GETOPT”
while true; do
case “$1″ in
-h|–help) echo “$USAGE”; exit 0 ;;
-c|–children) if [ "$2" -gt '0' ] >/dev/null 2>&1; then
MAXCHILDREN=”$2″;
shift;
shift;
else
echo “Number of children MUST be an integer.”;
exit 1;
fi
;;
-o|–stdout) TTYOUT=1; shift ;;
-l|–syslog) SYSLOGOUT=1; shift ;;
-d|–dry-run) TTYOUT=1; DRYRUN=1; shift ;;
-s|–status) TTYOUT=1; STATUSONLY=1; shift ;;
-f|–force) FORCE=1; shift ;;
–) shift; break ;;
*) echo “Invalid Option ${1}.”; echo “$USAGE”; exit 1 ;;
esac
done
Here’s yet another take on it:
http://codesnippets.joyent.com/posts/show/1697
@Doug — Why thanks. I especially appreciate the retarded bit. Cheers!
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