Shell Scripting Basics with Safe, Fail-Fast Bash

BeginnerLinux~3 hours
bashset -euo pipefailconditionalsshellcheck

I wrote reliable Bash scripts using a strict mode (set -euo pipefail), quoted variables, and conditionals, then linted with shellcheck. Fail-fast settings made scripts abort on the first error instead of silently continuing in a broken state.

Objective & Context

Most shell bugs come from unquoted variables and ignored errors. This lab establishes a safe scripting baseline and static analysis, the foundation the advanced scripting and sysadmin labs build on.

Environment & Prerequisites

  • Bash 5.x and shellcheck.
  • A task to automate (backup, report).
  • A test directory for safe execution.

Step-by-Step Execution

1. Strict-mode script skeleton

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'
target="${1:?usage: backup.sh DIR}"
tar -czf "backup-$(date +%F).tgz" "$target"

2. Lint before running

shellcheck backup.sh

3. Run and check exit status

./backup.sh /etc; echo "exit=$?"
In backup.sh line 5: (no issues found)
exit=0

Validation & Testing

Call the script with a missing argument and an invalid path and confirm it aborts with a clear non-zero exit. Pass criteria: shellcheck reports clean, undefined variables fail under -u, and errors abort under -e.

Advanced: Troubleshooting
  • Word splitting: always quote "$var"; set IFS deliberately.
  • Silent failures: set -e plus pipefail surfaces errors in pipelines.
  • Unset variable crashes: provide defaults with ${var:-default}.

Key Results

  • Adopted fail-fast strict mode as the script default.
  • Caught common bugs pre-run with shellcheck.
  • Eliminated word-splitting issues through consistent quoting.
  • Returned meaningful exit codes for pipeline integration.

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