Common Bash Script Requirements¶

Applies to both simple and complex Bash scripts.

Shebang & Safety Modes¶

Start every script with:

#!/usr/bin/env bash

set -o errexit -o nounset

errexit: exit immediately on error.
nounset: exit on reference to an unset variable.

Complex scripts additionally add -o errtrace (see developing-complex-bash-scripts.md).

SHOULD NOT add set -o pipefail globally; reserve it for critical pipe chains that must be checked.

Tooling¶

Scripts MUST pass shellcheck without warnings.
Format with shfmt -i=4 -ci before considering the script done.

Logic & Control Flow¶

MUST use [[ ... ]] for conditionals; MUST NOT use [ ... ].
SHOULD use case for pattern matching or multiple-branch decisions.
SHOULD prefer guard clauses to keep nesting shallow:

# Bad
if [[ -f "${file}" ]]; then
    process "${file}"
else
    echo "File not found" >&2
    exit 1
fi

# Good
if [[ ! -f "${file}" ]]; then
    echo "File not found: ${file}" >&2
    exit 1
fi
process "${file}"

Use declare -a for arrays and declare -A for associative arrays when working with structured data.
SHOULD use process substitution <(cmd) instead of temp files where possible.
SHOULD use here-strings <<<"str" for short single-line inputs.

Variables & Quoting¶

MUST use ${var} braces for variable expansion.
MUST quote expansions: "${var}" - this prevents word-splitting and glob expansion.
SHOULD use descriptive variable names; avoid magic numbers.

Output¶

Use echo or printf for normal output.
MUST write errors to stderr, e.g. echo "error message" >&2.