linux-bash-scripting

Linux Bash Scripting

Produce bash scripts that pass shellcheck --enable=all and shfmt -d with zero warnings.

Target: GNU Bash 4.4+ on Linux. No macOS/BSD workarounds, no Windows paths, no POSIX-only restrictions.

Script Foundation

#!/usr/bin/env bash
set -Eeuo pipefail
shopt -s inherit_errexit

SCRIPT_DIR=$(dirname -- "${BASH_SOURCE[0]}") || exit "$?"
SCRIPT_DIR=$(cd -- "${SCRIPT_DIR}" && pwd -P) || exit "$?"
readonly SCRIPT_DIR

trap 'printf "Error at %s:%d\n" "${BASH_SOURCE[0]}" "$LINENO" >&2' ERR
trap 'rm -rf -- "${_tmpdir:-}"' EXIT

• -E propagates ERR traps into functions
• inherit_errexit propagates errexit into $() command substitutions
• Resolve the script's own data files against SCRIPT_DIR, never the caller's cwd or git rev-parse --show-toplevel. A shared linter invoked from another project's git hook, a cron job, or a wrapper runs with someone else's cwd, so a caller-relative rules path resolves to a file that does not exist: the rule set loads empty, zero violations are found, exit 0. It is a silent no-op, not an error, and running it from inside its own repo passes for the wrong reason. Exercise it once from a scratch directory that is not the script's own tree
• Always create temp dirs under the EXIT trap: _tmpdir=$(mktemp -d)
• Wrap the body in a main function. Guard its invocation so direct execution runs it and sourcing only defines functions for testing.

Core rules

• Quote expansions, use arrays for commands, and never evaluate external data as shell code.
• Validate numeric syntax, sign, and application bounds before arithmetic. Convert unsigned digits with 10# before applying the sign; 10#-08 is invalid.
• Keep secrets out of process arguments and tracing. Feed them through stdin and use a JSON-aware encoder.
• Check exact exit statuses where “absent” differs from “failed to inspect.” Separate local and readonly declarations from command substitutions.
• Use NUL-delimited file iteration, validate required flag values, and reject conflicting output/target combinations.
• For atomic replacement, stage beside the destination; for multi-file activation, switch a single staged release reference.
• Preserve unrelated files and report the actual signal or command status after cleanup.
• Do not assume Bash options work in sh, GNU utility modes behave like syscall modes, or a configured fallback path is usable.