Handling options with null values in bash

[baijuw]

I am having a shell script that is triggered by an external program. This external program starts the shell script with a few options and values. The problem here is that the external script does not always fill all the options with values,it sometimes leaves option on the command line without any value attached to it. In that case the options which does not have a value assumes the next option to be its value

************Program code************************************
cat testing
#!/bin/bash
while getopts c:l:g:u:s:t:a:e:y:z option
do
case ${option} in
c) c=${OPTARG};;
l) l=${OPTARG};;
s) s=${OPTARG};;
g) g=${OPTARG};;
t) t=${OPTARG};;
a) a=${OPTARG};;
e) e=${OPTARG};;
u) u=${OPTARG};;
y) y=${OPTARG};;
z) z=${OPTARG};;
\?) echo " usage error"
exit;
esac
done

echo "c=$c"
echo "l=$l"
echo "s=$s"
echo "t=$t"
echo "a=$a"
echo "e=$e"
echo "g=$g"
echo "u=$u"
echo "y=$y"
echo "z=$z"
**********************End of program**************************

eg :-
./testing -a val1 -l val2 -g -u val4
output:-
c=
l=val2
s=
t=
a=val1
e=
g=-u
u=
y=
z=


Here we see that -g option assumes that -u is a value fed to it. This way I am loosing out on the last value val4. Is there a work around for this problem in bash?

[drl]

Hi.

Welcome to the forums.

It's much easier to read code if you use CODE tags -- select the text in the editing / composing window and then click the # just above the window.

Also no need to shout, most of us can read the standard-size text.

There is an external form of option processing. Here's an example of use:

#!/usr/bin/env bash

# @(#) s2       Demonstrate external getopt.

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) getopt
set -o nounset

echo
echo " Results:"

echo
echo " No arguments:"
./getopt-external -c1 -a

echo
echo " -c, no optional arg:"
./getopt-external -c -a

echo
echo " -c, no immediate following arg:"
./getopt-external -c 1 -a

exit 0

producing:

% ./s2

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.11-x1, i686
Distribution        : Xandros Desktop 3.0.3 Business
GNU bash 2.05b.0
getopt (enhanced) 1.1.3

 Results:

 No arguments:
Option c, argument `1'
Option a
Remaining arguments:

 -c, no optional arg:
Option c, no argument
Option a
Remaining arguments:

 -c, no immediate following arg:
Option c, no argument
Option a
Remaining arguments:
--> `1'

You might notice that the optional argument needs to be next to the option letter. Otherwise how could it tell what is legitimate and what is not?

You can find this code at: Getopt: Parse command-line arguments from shell scripts

It has other advantages, such as processing long arguments. You will, however, need to do some work -- get it, compile it, install it.

If you think this is too non-standard or too much work, I think the only other solution is to parse everything yourself. This usually means a long case statement. You are then not dependent on anything else, so you have good portability. I did this a few weeks ago when I thought users might miss an option. I checked for a leading "-" in the option.

Best wishes ... cheers, drl