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Linux Command Line & Bash Scripting Mastery · Lesson

Trap Handlers for Cleanup and Signals

Register EXIT, ERR, and INT traps to remove temp files and roll back partial work reliably.

Why Trap Handlers Matter

When a Bash script exits — whether normally, due to an error, or because the user pressed Ctrl+C — it can leave behind temporary files, half-written data, or broken state. Without cleanup, these artifacts accumulate and cause hard-to-debug problems.

Trap handlers solve this by registering a function or command that Bash executes automatically when a specific signal or pseudo-signal is received.

  • EXIT — fires whenever the script exits, for any reason
  • ERR — fires after any command returns a non-zero exit status
  • INT — fires when the user sends SIGINT (Ctrl+C)
  • TERM — fires on SIGTERM (e.g. from kill)

A well-written script registers these traps at the very top, before any risky work begins.

The trap Builtin Syntax

The trap builtin registers a handler for one or more signals or pseudo-signals. The general syntax is:

trap 'command_or_function' SIGNAL [SIGNAL...]

Key rules:

  • The first argument is a quoted string of shell code (or a function name) to execute when the signal fires.
  • You can list multiple signals after the handler.
  • trap '' SIGNAL ignores that signal (empty handler).
  • trap - SIGNAL resets the signal to its default behavior.

Traps are inherited by functions called in the same shell, but not by subshells spawned with ( ) or &.

#!/usr/bin/env bash
# Syntax examples — not a full script

# Register a cleanup function on EXIT
trap cleanup EXIT

# Inline handler for INT and TERM
trap 'echo "Interrupted!"; exit 1' INT TERM

# Ignore SIGHUP
trap '' HUP

# Reset SIGPIPE to default
trap - PIPE

All lessons in this course

  1. Strict Mode with set -euo pipefail
  2. Trap Handlers for Cleanup and Signals
  3. Safe Temporary Files and Lock Directories
  4. Idempotent Scripts and Retry-with-Backoff Logic
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