Bash Script Style and ShellCheck

A script template

#!/usr/bin/env bash
# Rotates application logs older than N days.
set -euo pipefail

readonly LOG_DIR="${LOG_DIR:-/var/log/app}"

main() {
  local days="${1:-7}"
  find "$LOG_DIR" -name '*.log' -mtime +"$days" -print -delete
}

main "$@"

Style rules that prevent bugs

• Quote every expansion: "$var", "$(cmd)", "${arr[@]}".
• Use [[ ]] instead of [ ], and $(...) instead of backticks.
• Put logic in functions with local variables and call main "$@" at the end.
• Prefer long options in scripts (--recursive) for readability.

ShellCheck

ShellCheck finds bugs such as unquoted variables, useless cat, and cd without error handling. Run it in your editor and in CI: shellcheck scripts/*.sh. For example, it flags rm -rf $dir/* (if dir is empty this becomes rm -rf /*) and suggests rm -rf "${dir:?}"/*.

dir=""
# ${dir:?} stops the command instead of expanding to an empty string
rm -rf "${dir:?}"/tmp 2>&1 | sed 's/^.*: line [0-9]*: //' || true
echo "nothing was deleted"

nothing was deleted

When to switch languages

Bash is great for gluing commands together. When a script needs data structures, JSON handling, or grows past a couple of hundred lines, Python or Go is usually easier to test and maintain.