How to create a function in Zsh

Aliases work well for fixed command text, but a reusable shell shortcut often needs arguments, branching, or a meaningful return status. Zsh functions keep that logic in the shell and invoke it with the same command-like syntax as external programs.

An interactive Zsh session reads ~/.zshrc, so placing a small function there makes it available whenever the file is loaded. Function arguments become positional parameters, while local keeps a scratch variable from replacing a name used by the calling shell.

Successful syntax validation proves that ~/.zshrc parses but does not prove that the function handles its input. A multiword name tests the argument boundary, while a no-argument call exposes the explicit usage error and nonzero return path.

1. Add the greet function shell with a local name parameter to ~/.zshrc.

   greet() {
       local name=${1-}
   }

   Functions in ~/.zshrc load alongside its existing interactive settings. The ${1-} expansion supplies an empty value when no first argument exists.

2. Insert the missing-name guard after the local declaration.

   if [[ -z $name ]]
   then
       print -u2 -- 'usage: greet <name>'
       return 2
   fi

   print -u2 sends the usage message to standard error, and return 2 lets the caller detect invalid input.

3. Place the greeting output before the closing brace.

   print -r -- "Hello, $name"

   The -r option prevents backslash escapes in the supplied name from being interpreted.

4. Compare the completed function in ~/.zshrc with the full definition.

   ~/.zshrc

   greet() {
       local name=${1-}
    
       if [[ -z $name ]]
       then
           print -u2 -- 'usage: greet <name>'
           return 2
       fi
    
       print -r -- "Hello, $name"
   }

5. Validate ~/.zshrc with Zsh for syntax errors.

   $ zsh -n ~/.zshrc

   No output means Zsh parsed the startup file without finding a syntax error.

6. Load the updated ~/.zshrc into the current Zsh session.

   $ source ~/.zshrc

7. Call greet without an argument to confirm its usage error.

   $ greet
   usage: greet <name>

8. Call greet with a quoted multiword name to verify argument handling.

   $ greet "Ada Lovelace"
   Hello, Ada Lovelace