wiki.bash-hackers.org/syntax/ccmd/case.md

# The case statement

## Synopsis

    case <WORD> in
      [(] <PATTERN1> ) <LIST1> ;; # or ;& or ;;& in Bash 4
      [(] <PATTERN2> ) <LIST2> ;;
      [(] <PATTERN3> | <PATTERN4> ) <LIST3-4> ;;
      ...
      [(] <PATTERNn>) <LISTn> [;;]
    esac

## Description

The `case`-statement can execute commands based on a [pattern
matching](/syntax/pattern.md) decision. The word `<WORD>` is matched
against every pattern `<PATTERNn>` and on a match, the associated
[list](/syntax/basicgrammar.md#lists) `<LISTn>` is executed. Every
commandlist is terminated by `;;`. This rule is optional for the very
last commandlist (i.e., you can omit the `;;` before the `esac`). Every
`<PATTERNn>` is separated from it's associated `<LISTn>` by a `)`, and
is optionally preceded by a `(`.

Bash 4 introduces two new action terminators. The classic behavior using
`;;` is to execute only the list associated with the first matching
pattern, then break out of the `case` block. The `;&` terminator causes
`case` to also execute the next block without testing its pattern. The
`;;&` operator is like `;;`, except the case statement doesn't terminate
after executing the associated list - Bash just continues testing the
next pattern as though the previous pattern didn't match. Using these
terminators, a `case` statement can be configured to test against all
patterns, or to share code between blocks, for example.

The word `<WORD>` is expanded using *tilde*, *parameter* and *variable
expansion*; *arithmetic*, *command* and *process substitution*; and
*quote removal*. **No word splitting, brace, or pathname expansion is
done**, which means you can leave expansions unquoted without problems:

    var="test word"

    case $var in
      ...
    esac

This is similar to the behavior of the [conditional expression command
("new test command")](/syntax/ccmd/conditional_expression.md) (also no word
splitting for expansions).

Unlike the C-case-statement, only the matching list and nothing else is
executed. If more patterns match the word, only the first match is
taken. (**Note** the comment about Bash v4 changes above.)

Multiple `|`-delimited patterns can be specified for a single block.
This is a POSIX-compatable equivalent to the `@(pattern-list)` extglob
construct.

The `case` statement is one of the most difficult commands to indent
clearly, and people frequently ask about the most "correct" style. Just
do your best - there are many variations of indenting style for `case`
and no real agreed-upon best practice.

## Examples

Another one of my stupid examples...

    printf '%s ' 'Which fruit do you like most?'
    read -${BASH_VERSION+e}r fruit

    case $fruit in
        apple)
            echo 'Mmmmh... I like those!'
            ;;
        banana)
            echo 'Hm, a bit awry, no?'
            ;;
        orange|tangerine)
            echo $'Eeeks! I don\'t like those!\nGo away!'
            exit 1
            ;;
        *)
            echo "Unknown fruit - sure it isn't toxic?"
    esac

Here's a practical example showing a common pattern involving a `case`
statement. If the first argument is one of a valid set of alternatives,
then perform some sysfs operations under Linux to control a video card's
power profile. Otherwise, show a usage synopsis, and print the current
power profile and GPU temperature.

``` bash
# Set radeon power management
function clk {
    typeset base=/sys/class/drm/card0/device
    [[ -r ${base}/hwmon/hwmon0/temp1_input && -r ${base}/power_profile ]] || return 1

    case $1 in
        low|high|default)
            printf '%s\n' "temp: $(<${base}/hwmon/hwmon0/temp1_input)C" "old profile: $(<${base}/power_profile)"
            echo "$1" >${base}/power_profile
            echo "new profile: $(<${base}/power_profile)"
            ;;
        *)
            echo "Usage: $FUNCNAME [ low | high | default ]"
            printf '%s\n' "temp: $(<${base}/hwmon/hwmon0/temp1_input)C" "current profile: $(<${base}/power_profile)"
    esac
}
```

A template for experiments with `case` logic, showing shared code
between blocks using `;&`, and the non-short-circuiting `;;&` operator:

``` bash
#!/usr/bin/env bash

f() {
    local -a "$@"
    local x

    for x; do
        case $x in
            $1)
                local "$x"'+=(1)' ;;&
            $2)
                local "$x"'+=(2)' ;&
            $3)
                local "$x"'+=(3)' ;;
            $1|$2)
                local "$x"'+=(4)'
        esac
        IFS=, local -a "$x"'=("${x}: ${'"$x"'[*]}")'
    done

    for x; do
        echo "${!x}"
    done
}

f a b c

# output:
# a: 1,4
# b: 2,3
# c: 3
```

## Portability considerations

- Only the `;;` delimiter is specified by POSIX.
- zsh and mksh use the `;|` control operator instead of Bash's `;;&`.
  Mksh has `;;&` for Bash compatability (undocumented).
- ksh93 has the `;&` operator, but no `;;&` or equivalent.
- ksh93, mksh, zsh, and posh support a historical syntax where open and
  close braces may be used in place of `in` and `esac`:
  `case word { x) ...; };`. This is similar to the alternate form Bash
  supports for its [for loops](syntax/ccmd/classic_for), but Bash
  doesn't support this syntax for `case..esac`.

## See also

- [POSIX case conditional
  construct](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_04_05)