Functions

Define and call

Functions behave like simple commands. Pass arguments as $1… inside.

greet() {
  local who="${1:-world}"
  printf 'Hello, %s\n' "$who"
}
greet Ada

Return status vs stdout

return sets the exit status (0–255). Print results to stdout; check status with $?.

is_file() {
  [[ -f "$1" ]]
}
if is_file "notes.txt"; then echo yes; fi

Prefer locals

Without local, assignments affect the global scope and cause subtle bugs.

Keep functions focused

One job per function. Name them with verbs: backup_files, require_cmd.

require_cmd() {
  command -v "$1" >/dev/null || {
    echo "missing: $1" >&2
    exit 127
  }
}