| name | writing-robust-bash |
| description | Use when writing or reviewing bash/shell scripts. Covers strict mode, quoting, error handling and cleanup traps, safe command usage, and bash-vs-POSIX portability so scripts fail loudly instead of silently doing the wrong thing. |
Writing robust bash
A shell script's default behavior is to plow ahead after an error. Robust scripts opt out of
that: fail fast, quote everything, and clean up after themselves.
Strict mode
Start non-trivial bash scripts with:
#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'
-e exit on error, -u error on unset variables, -o pipefail so a failure mid-pipe
isn't masked by a later success.- Narrowing
IFS avoids surprise word-splitting on spaces.
Quoting
- Quote every expansion:
"$var", "$@", "${arr[@]}". Unquoted expansions split on
whitespace and glob.
- Use
"$@" (not $*) to forward arguments intact.
- Prefer
printf '%s\n' "$x" over echo "$x" for values that may start with - or contain
escapes.
Errors & cleanup
- Use a trap for cleanup so temp files go away on any exit:
tmp=$(mktemp); trap 'rm -f "$tmp"' EXIT.
- Check that required commands exist:
command -v jq >/dev/null || { echo "need jq" >&2; exit 1; }.
- Send diagnostics to stderr (
>&2) and return meaningful exit codes.
Safe patterns
- Prefer
[[ … ]] over [ … ] in bash; it's safer with empty vars and supports =~.
- Don't parse
ls; use globs or find … -print0 with read -d ''.
- Use
local for function variables so they don't leak into the global scope.
- Quote command substitutions:
count="$(wc -l < "$file")".
Portability
- If the shebang is
#!/bin/sh, you're in POSIX territory: no [[ ]], no arrays, no
local (in strict POSIX). Either target bash explicitly or stay within POSIX.
set -euo pipefail is bash; plain POSIX sh supports only set -eu.
American English in comments and messages.
