Safe, robust Bash script: error handling, locking, logs and dry-run

Prompt

Act as a Linux systems administrator who writes maintainable, safe shell scripts.

I need a script that does the following: {{task}}
- Environment it will run in: {{environment}}
- Inputs (arguments, files, variables): {{inputs}}
- What it modifies or deletes: {{effects}}

Deliverables:
1. The complete script with:
   - A shebang suited to the environment and strict mode (`set -Eeuo pipefail`) or its equivalent if the shell is not Bash, explaining its gotchas.
   - A `usage` function and argument parsing with `getopts`, including `-h`, `-v` (verbose) and `-n` (dry-run).
   - A dependency check with `command -v` and clear messages when something is missing.
   - Variables always quoted, `local` inside functions and no `eval`.
   - Temp files via `mktemp` and cleanup with `trap` on `EXIT`, `INT` and `TERM`.
   - A lock with `flock` (or a portable alternative) to prevent two simultaneous runs.
   - Timestamped logs to stderr and optionally to a file.
   - Documented exit codes.
   - In dry-run mode, print what it would do without running anything destructive.
2. An explanation of each block and of any dangerous line (deletions, permissions, `sudo`).
3. How to verify it: ShellCheck with no warnings, plus a few bats-core tests or a manual procedure in a scratch directory.
4. How to schedule it with cron or a systemd timer if that makes sense, including the PATH and variables it needs.

Constraints:
- Any `rm` or overwrite must first check that the path is not empty and not `/`.
- Do not invent paths or server names: use mine or [FILL IN].
- If the task is ambiguous or dangerous, ask me before writing the script.
- Recommend testing with `-n` first and outside production.

How to use it

Usage example

Sample output

#!/usr/bin/env bash
# rotate-logs.sh — compress .log older than N days, delete .gz older than M days
set -Eeuo pipefail

LOG_DIR="/var/log/myapp"; COMPRESS_DAYS=7; DELETE_DAYS=30
DRY_RUN=0; VERBOSE=0; LOCK="/run/lock/rotate-logs.lock"

log()   { printf '%s [%s] %s\n' "$(date '+%F %T')" "$1" "$2" >&2; }
usage() { echo "Usage: ${0##*/} [-h] [-v] [-n] [-d dir] [-c days] [-r days]"; }
run()   { if (( DRY_RUN )); then log DRY "$*"; return 0; fi
          if (( VERBOSE )); then log INFO "$*"; fi; "$@"; }

while getopts ":hvnd:c:r:" opt; do
  case "$opt" in
    h) usage; exit 0 ;;  v) VERBOSE=1 ;;  n) DRY_RUN=1 ;;
    d) LOG_DIR="$OPTARG" ;;  c) COMPRESS_DAYS="$OPTARG" ;;  r) DELETE_DAYS="$OPTARG" ;;
    *) usage; exit 1 ;;
  esac
done

# Never operate on an empty path or on /
[[ -n "$LOG_DIR" && "$LOG_DIR" != "/" && -d "$LOG_DIR" ]] || { log ERROR "invalid directory: $LOG_DIR"; exit 2; }
[[ "$COMPRESS_DAYS$DELETE_DAYS" =~ ^[0-9]+$ ]] || { log ERROR "days must be integers"; exit 1; }
command -v gzip >/dev/null || { log ERROR "gzip is missing"; exit 3; }

exec 9>"$LOCK"; flock -n 9 || { log WARN "another run is in progress"; exit 4; }

find "$LOG_DIR" -type f -name '*.log' -mtime +"$COMPRESS_DAYS" -print0 |
  while IFS= read -r -d '' f; do run gzip -- "$f"; done
find "$LOG_DIR" -type f -name '*.gz' -mtime +"$DELETE_DAYS" -print0 |
  while IFS= read -r -d '' f; do run rm -f -- "$f"; done

Key facts

Category

Programming & development · Automations

Output type

Code

Level

Intermediate

Designed for

ChatGPT, Claude, Gemini and Microsoft Copilot

Verified in

Pending editorial verification

Variables

Task, Environment, Inputs and What it modifies or deletes

Language

English

Price

Free, no sign-up

Updated

Nov 7, 2026

Frequently asked questions