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

choroba · Accepted Answer · 2023-05-11 08:48:13Z

28

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

edited May 11, 2023 at 8:48

answered Nov 6, 2012 at 16:07

choroba

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3 Comments

anubhava Over a year ago

+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.

siebz0r Over a year ago

This is awesome! Thanks! @anubhava Why would your suggestion be better (@ instead of +)?

siebz0r Over a year ago

@anubhava Never mind, found it here. @ matches one occurrence, + matches multiple.

Peter Mortensen · Accepted Answer · 2022-03-01 17:35:17Z

3

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.

edited Mar 1, 2022 at 17:35

Peter Mortensen

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answered Nov 6, 2012 at 15:48

sampson-chen

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1 Comment

siebz0r Over a year ago

@Guru is right. This only matches the first since test becomes aaa.

Peter Mortensen · Accepted Answer · 2022-03-01 17:47:18Z

2

Using eval also works:

eval 'case "$1" in

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

edited Mar 1, 2022 at 17:47

Peter Mortensen

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answered Jul 1, 2016 at 20:23

mliberi

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2 Comments

Peter Mortensen Over a year ago

But eval is evil(?).

Peter Mortensen Over a year ago

"The command eval is a very risky command"

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