"unbound variable" reading a boolean parameter from shell script command line

Question

My apology for not being able to find such a seemingly trivial thing myself.

I need to pass more than one boolean parameter to shell script (Bash) as follows:

./script --parameter1 --parameter2

and so on.

All are to be considered true if set.

In the beginning of the script, I use set -u.

Normal parameter with value passing I currently do as follows:

# this script accepts the following arguments:
# 1. mode
# 2. window

while [[ $# > 1 ]]
do

    cmdline_argument="$1"

    case $cmdline_argument in

        -m|--mode)

            mode="$2"
            shift

        ;;

        -w|--window)

            window="$2"
            shift

        ;;

    esac

    shift

done

I would like to add something like

    -r|--repeat)

        repeat=true

        shift

    ;;

I do not understand why it does not work as expected.

It exits immediately with error:

./empire: line 450: repeat: unbound variable

Where the line 450 is:

if [ "$repeat" == true ];

Can you clarify how it fails? Is it because you're missing a shift? — Gordon Davisson
– Gordon Davisson, Commented Jun 17, 2017 at 2:21
See BashFAQ #112. And on a related note, definitely read BashFAQ #105 before using set -e. — Charles Duffy
– Charles Duffy, Commented Jun 17, 2017 at 2:56

Charles Duffy · Accepted Answer · 2017-06-17 02:55:54Z

6

When you use set -u, it's an error to dereference any variable that hasn't had a value explicitly assigned.

Thus, you need to set repeat=0 (or repeat=false) at the top of your script, or to use a dereference method that has an explicit default behavior when the value is unset; see BashFAQ #112.

answered Jun 17, 2017 at 2:55

Charles Duffy

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