Using a variable as a case pattern in Bash

Question

I'm trying to write a Bash script that uses a variable as a pattern in a case statement. However, I just cannot get it to work.

Case statement:

case "$1" in
    $test)
        echo "matched"
        ;;
    *)
        echo "didn't match"
        ;;
esac

I've tried this with assigning $test as aaa|bbb|ccc, (aaa|bbb|ccc), [aaa,bbb,ccc] and several other combinations. I also tried these as the pattern in the case statement: @($test), @($(echo $test)), $($test). Also no success.

For clarity, I would like the variable to represent multiple patterns like this:

case "$1" in
    aaa|bbb|ccc)
        echo "matched"
        ;;
    *)
        echo "didn't match"
        ;;
esac

score 25 · Accepted Answer · answered Nov 06 '12 at 16:07

25

You can use the extglob option:

#! /bin/bash

shopt -s extglob         # enables pattern lists like +(...|...)
test='+(aaa|bbb|ccc)'

for x in aaa bbb ccc ddd ; do
    echo -n "$x "
    case "$x" in
        $test) echo Matches.
        ;;
        *) echo Does not match.
    esac
done

answered Nov 06 '12 at 16:07

choroba

216,930
22
195
267

2

+1 for reminding me the use of `extglob`. By the way `test='@(aaa|bbb|ccc)'`also works and is probably better option in this case. – anubhava Nov 06 '12 at 16:14
This is awesome! Thanks! @anubhava Why would your suggestion be better (@ instead of +)? – siebz0r Nov 06 '12 at 16:19
1

@anubhava Never mind, found it [here](https://www.gnu.org/software/bash/manual/html_node/Pattern-Matching.html#Pattern-Matching). @ matches one occurrence, + matches multiple. – siebz0r Nov 06 '12 at 16:22

score 3 · Answer 2 · edited Mar 01 '22 at 17:35

Here's something a bit different:

#!/bin/bash

pattern1="aaa bbb ccc"
pattern2="hello world"
test=$(echo -e "$pattern1\n$pattern2" | grep -e $1)

case "$test" in
    "$pattern1")
        echo "matched - pattern1"
        ;;
    "$pattern2")
        echo "matched - pattern2"
        ;;
    *)
        echo "didn't match"
        ;;
esac

This makes use of grep to do the pattern matching for you, but still allows you to specify multiple pattern sets to be used in a case-statement structure.

For instance:

If either aaa, bbb, or ccc is the first argument to the script, this will output matched - pattern1.
If either hello or world is the first argument, this will output matched - pattern2.
Otherwise it will output didn't match.

@Guru is right. This only matches the first since `test` becomes `aaa`. — siebz0r, Nov 06 '12 at 15:52

score 2 · Answer 3 · edited Mar 01 '22 at 17:47

2

Using eval also works:

eval 'case "$1" in

    '$test')
        echo "matched"
        ;;
    *)
        echo "did not match"
        ;;
esac'

edited Mar 01 '22 at 17:47

Peter Mortensen

30,030
21
100
124

answered Jul 01 '16 at 20:23

mliberi

29
2

But *eval* is evil(?). – Peter Mortensen Mar 01 '22 at 17:37
*["The command `eval` is a very risky command"](https://stackoverflow.com/questions/874389/test-for-a-bash-variable-being-unset-using-a-function#comment48595199_6006055)* – Peter Mortensen Mar 01 '22 at 17:57

Using a variable as a case pattern in Bash

3 Answers3

Linked