Functions

Group reusable logic with shell functions.

Defining functions

hello() {
  echo "Hello, $1"
}
hello "Ada"

Names share the global namespace; prefer unique prefixes for libraries.

Local variables and scope

inc() {
  local x=${1:-0}
  ((x++))
  echo "$x"
}
count=$(inc 41)

local restricts scope inside a function.

Returning values

• Use echo/printf to output data and capture with command substitution
• Use return <code> for success/failure (0–255)

validate() { [[ $1 =~ ^[0-9]+$ ]] || return 1; }
if validate "$age"; then echo ok; fi

Arguments and $@

myfn() {
  for arg in "$@"; do echo "$arg"; done
}

Sourcing and libraries

# lib.sh
say() { echo "[$(date +%T)] $*"; }

# script.sh
source ./lib.sh
say "start"

Error handling

Combine with set -euo pipefail and check statuses. Use traps for cleanup.

trap 'echo cleanup; rm -f "$tmp"' EXIT

Summary

• Functions return data via stdout and status via return
• Use local, quote args, and prefer sourcing for reuse