Exit Status and Error Handling

Write robust scripts that fail early and clean up properly.

Exit status

• 0 = success; non-zero = failure
• $? holds the last command’s status

cmd
status=$?
if (( status != 0 )); then echo "failed: $status"; fi

set -euo pipefail

set -euo pipefail
# -e: exit on error
# -u: undefined var is an error
# -o pipefail: pipeline fails if any stage fails

Caveats: -e is disabled in some contexts (subshells, conditionals). Prefer explicit checks where critical.

Traps

tmp=$(mktemp)
trap 'rm -f "$tmp"' EXIT

Run cleanup on exit (success or error). Add INT/TERM for signals.

ERR trap and functions

set -E  # inherit ERR in functions
trap 'echo "error on line $LINENO"' ERR

Guarded commands

rm -rf -- "$dir" || { echo "rm failed"; exit 1; }

Retry pattern

for i in {1..3}; do cmd && break; sleep 1; done

Logging

log() { printf '[%(%F %T)T] %s\n' -1 "$*"; }

Summary

• Check exit codes; enable -euo pipefail thoughtfully
• Use traps for cleanup and ERR for diagnostics