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Bash functions are simpler than they look — and trickier than they look.

greet() {
    local name="$1"            # ALWAYS use 'local' for parameters
    echo "Hello, $name"
}

greet "Ada"

Bash functions don't really return values — they return an exit status (0-255). To return data, write to stdout:

add() {
    echo $(( $1 + $2 ))         # output the result
}

result=$(add 3 4)               # capture stdout
echo "$result"                  # 7

$1, $2, ... are positional arguments. $# is the count. $@ is all arguments (use quoted: "$@").

local is critical** — without it, every variable is global. Forgetting local is the #1 source of bash bugs:

count() {
    local i
    for ((i = 1; i <= 5; i++)); do
        echo $i
    done
}

Returning structured data — bash can't return arrays. Workarounds:

• Print one element per line, capture with mapfile:

  list_users() {
      echo "alice"; echo "bob"; echo "carol"
  }
  mapfile -t users < <(list_users)
  

• Set a global variable
• Use a nameref (Bash 4.3+):

  populate() {
      local -n out=$1
      out=(a b c)
  }
  populate myarr