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.

1. 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.

2. Check the script syntax.

   $ bash -n service-action.sh

3. Run the default status branch.

   $ bash service-action.sh
   service is running

4. Run a single-pattern branch.

   $ bash service-action.sh start
   starting service

5. Run a branch shared by two patterns.

   $ bash service-action.sh reload
   refreshing service

6. 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.

7. Remove the sample script when the branch tests are finished.

   $ rm -f service-action.sh