Exit Codes & Debugging

Exit Codes

Every command returns an exit status: 0 = success, non-zero = failure. Scripts should exit with a meaningful code.

if ! command -v git >/dev/null; then
  echo 'git missing' >&2
  exit 1
fi

Idiom	Meaning
`cmd && echo ok`	run echo only if cmd succeeded
`cmd \	\	echo fail`	run echo only if cmd failed
`cmd; echo $?`	print last exit code

Debugging: run with bash -x script.sh or add set -x to trace each line as it executes.

Exam tip: Conventionally exit codes 1-125 are script/command errors, 126 = not executable, 127 = command not found, 130 = terminated by Ctrl+C (128+SIGINT).