[SOLVED] shell scripting: value of argument dissapears depending on argument order

akelder · 03-21-2011, 01:38 AM

Examples:

Code:

$ ./test.sh -a -c 2
operator is -gt
remcount is
            ^ value missing!

Code:

$ ./test.sh -b -c 2
operator is -lt
remcount is
            ^ value missing!

Yet when "-c" is the first argument, its value is present:

Code:

$ ./test.sh -c 2 -b
operator is -lt
remcount is 2

What could I do to ensure the value of "-c" is picked up regardless of the argument order?

Script:

Code:

#!/bin/bash

while [ "$1" ]; do
  case "$1" in
        -a|--above)
        shift
            operator="-gt"
            ;;
        -b|--below)
        shift
            operator="-lt"
            ;;
        -c|--count)
        shift
            remcount="$1"
            ;;
        -h|--help)
        usage
        exit 0
            ;;
    -*)
        echo "$(basename $0): invalid option $1" >&2
        echo "see --help for usage"
        exit 1
        ;;
    *)
        break
        ;;
  esac
  shift
done

echo operator is $operator
echo remcount is $remcount

grail · 03-21-2011, 02:17 AM

Have a look at your entries for '-a' and '-b' closely and you may see the error of your ways.

The hint is that neither of these are expecting another argument.

akelder · 03-21-2011, 11:56 AM

Ok, thanks, using "shift 2" for the argument with a value seems to solve this. Is that the correct solution?

Code:

#!/bin/bash

while [ "$1" ]; do
  case "$1" in
        -a|--above)
            operator="-gt"
            shift
            ;;
        -b|--below)
            operator="-lt"
            shift
            ;;
        -c|--count)
            remcount="$2"
            shift 2
            ;;
        -h|--help)
        usage
        exit 0
            ;;
    -*)
        echo "$(basename $0): invalid option $1" >&2
        echo "see --help for usage"
        exit 1
        ;;
    *)
        break
        ;;
  esac
done

echo operator is $operator
echo remcount is $remcount

Code:

$ ./test.sh -c 2 -b
operator is -lt
remcount is 2

Code:

$ ./test.sh -a -c 2
operator is -gt
remcount is 2

Code:

$ ./test.sh -b -c 2
operator is -lt
remcount is 2

akelder · 03-21-2011, 12:03 PM

And also getting rid of that last "shift" after "esac"..

grail · 03-21-2011, 10:11 PM

Well that does work, but I am usually a proponent for using commands as few times as possible.
So the other way to look at it is that you leave the shift after the esac but remove from all but '-c' option as it
is the only one that requires more than a single shift.

You may also want to have a look at the getopts option, although long command options are not supported.

akelder · 03-21-2011, 11:27 PM

Quote:

Originally Posted by grail

leave the shift after the esac but remove from all but '-c' option as it
is the only one that requires more than a single shift.

Oh, yeah, that's definitely better. Thanks!