How to use a case statement in Zsh

A Zsh case statement lets a script choose one branch from a fixed set of words or shell patterns. It fits command dispatch, environment selection, and menu-style script arguments where a long chain of string comparisons would be harder to scan.

Each branch starts with a pattern ending in ) and ends with ;;. Multiple accepted words can share one branch with |, and a final * branch catches values that do not match any earlier pattern.

The example maps a target name to a URL, validates the file with zsh -n, and runs matched and unmatched inputs. Known targets print the selected URL, while empty or unknown targets print guard messages instead of a URL.

1. Create a script that matches the first argument against target names.

   deploy-target.zsh

   #!/usr/bin/env zsh
   emulate -L zsh
   setopt err_exit no_unset
    
   target=${1:-}
    
   case "$target" in
       dev|development)
           url="https://dev.example.com"
           ;;
       staging)
           url="https://staging.example.com"
           ;;
       production|prod)
           url="https://www.example.com"
           ;;
       "")
           print -u2 -- "missing target"
           exit 1
           ;;
       *)
           print -u2 -- "unknown target: $target"
           exit 1
           ;;
   esac
    
   print -r -- "target=$target"
   print -r -- "url=$url"

   The dev|development and production|prod branches accept two words each. The quoted empty-string branch handles a missing argument before the fallback * branch handles unsupported targets.

2. Check the script syntax before running it.

   $ zsh -n deploy-target.zsh

   No output from zsh -n means Zsh parsed the case block, branch endings, and esac marker without finding a syntax error.

3. Run a target that has one exact branch.

   $ zsh deploy-target.zsh staging
   target=staging
   url=https://staging.example.com

4. Run a target from a branch that also accepts a short alias.

   $ zsh deploy-target.zsh production
   target=production
   url=https://www.example.com

5. Confirm that an unsupported target reaches the fallback branch.

   $ zsh deploy-target.zsh sandbox
   unknown target: sandbox

   Keep the fallback * branch last. Earlier patterns are tested first, so a leading * branch would catch every value before the specific branches can run.

6. Confirm that a missing target reaches the empty-string branch.

   $ zsh deploy-target.zsh
   missing target

7. Remove the sample script after testing.

   $ rm -f deploy-target.zsh