CODEWITHSUNDEEP
bash
John
John

Reputation: 11861

Does starting parenthesis in Bash case statement have meaning?

I have found a case statement in a Bash script which looks like this:

case $i in
    (0) set -- ;;
    (1) set -- "$args0" ;;
    (2) set -- "$args0" "$args1" ;;
    (3) set -- "$args0" "$args1" "$args2" ;;
    (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
    (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
    (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
    (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
    (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
    (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
esac

I've never seen the use of a starting (, I've only ever seen SOME_CASE) command list ;;. I can't find any reference to this other format - does this starting parenthesis have any special significance?

Upvotes: 6

Views: 1012

Answers (2)

Ilia Dmitriev
Ilia Dmitriev

Reputation: 182

According to:

man 1 bash

the format of the case operator is:

case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac

The opening bracket is in square brackets, which means it's not required.

Upvotes: 3

Jonathan Leffler
Jonathan Leffler

Reputation: 754520

The starting parenthesis is optional, but it (usually) leaves balanced parentheses which makes it easier in editors like vim which can jump from a close bracket (such as ), ], }) to the matching open bracket, accounting for nested brackets. It has no other significance.

The original Bourne shell did not support the leading open parenthesis.

See also the POSIX shell specification for case under Compound commands or the Bash manual under Conditional Constructs.

It also looks as if your script is crying out to use a Bash array (see also Shell Parameters).

declare -a args

args+=("argument 0")
args+=("argument 1")
args+=("argument 2" "argument 3" "argument 4 with spaces")

set -- "${args[@]}"

No case; no limit on the number of arguments. How you build the array is open to discussion, but the one line instead of a 10-way case is compelling.

Upvotes: 8

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