How to use a case statement in Bash

A Bash case statement matches one value against several named patterns and runs the branch for the first match. It is easier to scan than a long if and elif chain when one argument selects actions such as start, stop, status, or reload.

The block starts with case "$value" in, each pattern line ends with ), each branch finishes with ;;, and the whole block closes with esac. Multiple accepted words can share one branch by separating patterns with |, while * is commonly used as the fallback branch.

A service-style action script can use the first argument as the action and fall back to status when no argument is supplied. Branch tests should cover the default action, a single-pattern branch, a shared-pattern branch, and the failure path that returns a nonzero status.

Steps to use a case statement in Bash:

Create a script that dispatches on the first argument.

service-action.sh

#!/usr/bin/env bash
set -euo pipefail
 
action=${1:-status}
 
case "$action" in
    start)
        printf "starting service\n"
        ;;
    stop)
        printf "stopping service\n"
        ;;
    status)
        printf "service is running\n"
        ;;
    restart|reload)
        printf "refreshing service\n"
        ;;
    *)
        printf "unknown action: %s\n" "$action" >&2
        exit 2
        ;;
esac

Quote the value being matched so an empty or space-containing argument is still treated as one value.

Check the script syntax.
```
$ bash -n service-action.sh
```

Run the default status branch.

$ bash service-action.sh
service is running

Run a single-pattern branch.

$ bash service-action.sh start
starting service

Run a branch shared by two patterns.

$ bash service-action.sh reload
refreshing service

Verify that an unknown action prints an error and exits with status 2.
```
$ bash service-action.sh remove
unknown action: remove
$ printf 'exit=%s\n' "$?"
exit=2
```
Capture the exit status immediately after the command being tested. Running another command first replaces $? with that command's status.
Remove the sample script when the branch tests are finished.
```
$ rm -f service-action.sh
```