Quick Answer
Select signals (EXIT, ERR, INT, TERM) and cleanup actions, then copy the generated trap block into your script header.
What is the difference between trap EXIT and trap ERR in bash?
EXIT fires every time the script exits, regardless of why — success, failure, or Ctrl+C. ERR fires when a command returns a non-zero exit code, under the same rules set -e uses (not inside if or while tests, or before || and &&); it does not need set -e, and it only reaches inside functions when set -E is on. For cleanup that must always run, use EXIT. For logging failures at the exact line they occur, use ERR.
Should I use single or double quotes in a bash trap statement?
Single quotes in most cases. With double quotes, variables expand immediately when the trap line is parsed, capturing their value at that moment. With single quotes, expansion happens when the trap fires, which is usually what you want. Exception: if you want to capture the current value of $TMPFILE at trap-definition time, double quotes are correct.
Will trap EXIT run if my script calls exit 1?
Yes. EXIT fires on any exit, including explicit exit 1, set -e failures, and SIGTERM. The only way to prevent a trap from running is to kill the script with SIGKILL (kill -9), which cannot be trapped.
How do I pass the exit code to my trap handler so I can log success vs failure?
Capture $? as the first line inside your handler function: local exit_code=$?. After that point $? reflects the cleanup commands themselves, so capture it immediately on entry.
Does trap work with set -euo pipefail?
Yes, and they complement each other. set -e causes the ERR trap to fire on any non-zero exit code. set -u exits with code 1 on unbound variables, triggering the EXIT trap. set -o pipefail propagates pipe failures through the ERR trap. The combination gives complete coverage.
An operational script system + a 30-function shared library + a 52-page field guide. The production layer the free snippets don't cover.
Get the Toolkit →Ten functions I source into every script on my own boxes — strict-mode setup, an ERR trap that names the failing line, lock and timeout wrappers, and cleanup that runs on every exit path. One email, no sequence.
#!/bin/bash # Script: myscript.sh # Purpose: A script without a trap leaves temp files, locks, and jobs behind when it crashes. # Usage: ./myscript.sh set -Eeuo pipefail CHECK="✓" CROSS="✗" _CLEANED=0 # guard so cleanup runs exactly once # Create the temp file up front so the trap can always remove it. TMPFILE=$(mktemp) # One handler for every trapped signal. Args: $1 exit code, $2 line, $3 signal. cleanup() { local exit_code="$1" local line_no="$2" local sig="${3:-EXIT}" # ERR and EXIT can both fire on one failure; run the body only once. if [[ "${_CLEANED:-0}" -ne 1 ]]; then _CLEANED=1 # Remove the temp file so a crash never leaves it behind. rm -f "$TMPFILE" # Report why we exited: non-zero is a failure, zero is clean. if (( exit_code != 0 )); then echo "$CROSS [$sig] failed: exit $exit_code near line $line_no" >&2 else echo "$CHECK [$sig] clean exit" fi fi } # Single quotes: cleanup is resolved when the signal fires, not at definition (SC2064). trap 'cleanup $? $LINENO EXIT' EXIT trap 'cleanup $? $LINENO ERR' ERR
set -euo pipefail? Read the full pattern in Bash Error Handling →| Signal | When it fires | Common use case |
|---|---|---|
| EXIT (0) | Script exits for any reason — success, failure, or interrupt. | The one trap that always runs. Put resource teardown here. |
| ERR | A command returns a non-zero exit code, under the same rules as set -e (not in if/while tests or before || / &&). Does not need set -e; without set -E it does not fire inside functions. | Log the exact failing line with $LINENO before the script dies. |
| INT (2) | User presses Ctrl+C at the terminal. | Print an interrupted message and exit 130 so callers see it was cancelled. |
| TERM (15) | kill, systemctl stop, or docker stop sends SIGTERM. | Graceful shutdown of long-running scripts and Docker entrypoints. |
| HUP (1) | Terminal closes or the SSH session drops. | Decide whether to abort or keep running when the session is lost. |
| PIPE | Writing to a pipe whose reader has closed (e.g. head exited early). | Suppress broken-pipe noise; usually handled rather than aborted on. |