language-bash

Bash

Strict mode

set -euo pipefail
IFS=$'\n\t'

• -e is suppressed in conditional contexts (||, &&, if, !); explicit subshells (...) do inherit it — use || true to absorb expected failures.
• -u treats unset variables as errors; unset arrays trigger it: declare before use (arr=()) or guard with ${arr[@]+"${arr[@]}"} for optional arrays.
• IFS=$'\n\t' prevents accidental word-splitting on spaces in for loops and command substitution.

Quoting and tests

• Always "$var" — bare $var triggers word splitting and glob expansion.
• 'literal' for fixed strings with no expansion needed.
• Prefer [[ ]] over [ ]: supports =~ regex, no word splitting, lexical string comparison.
• $() over backticks: nestable, readable, no escaping required.

if [[ "$filename" =~ \.(sh|bash)$ ]]; then
  shellcheck "$filename"
fi

Parameter expansion

• ${var:-default} — substitute default if unset or empty.
• ${var:?error msg} — abort with message if unset; pairs well with set -u.
• ${var%suffix} — strip shortest suffix match (e.g. strip extension).
• ${var//pattern/repl} — replace all occurrences in-place.

Arrays and word splitting

files=(src/a.sh "src/b script.sh" src/c.sh)
for f in "${files[@]}"; do   # each element quoted separately
  process "$f"
done

• "${arr[@]}" — each element as a separate quoted word; always use for iteration.
• "${arr[*]}" — all elements joined by IFS[0]; use only for joining to a string.
• Never for x in $(cmd) — use mapfile -t arr < <(cmd) or while IFS= read -r line.

Pipelines and subshells

• pipefail makes a pipeline fail when any stage fails, not just the last.
• Command substitution $(...) runs in a subshell; variable assignments inside don't leak out.
• cmd || true absorbs an expected non-zero exit under -e; cmd 2>/dev/null suppresses stderr noise separately.
• Background jobs: proc &; always wait "$pid" before consuming results.
• Redirect ordering matters: cmd >/dev/null 2>&1 silences all; cmd 2>&1 >/dev/null silences stdout only (stderr still shows — order determines what 2>&1 copies).