Code-Memo

Bash scripting fundamentals

Goals

• Write executable scripts with predictable behavior
• Understand shebang, exit codes, and basic structure

Minimal script template

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

main() {
  echo "Hello from a script"
}

main "$@"

Core concepts

• Shebang: #!/usr/bin/env bash selects Bash via PATH
• Executable bit: chmod +x script.sh
• Exit status: 0 success, non-zero failure; access via $?
• Args:
  • $0 script name, $1..$n positional args
  • $@ all args (safe when quoted), $# arg count
• Quoting:
  • Prefer "$var"; avoid unquoted expansions
  • "$@" preserves argument boundaries; "$*" joins

Useful builtins

• read -r var (avoid backslash escapes)
• [[ ... ]] for tests (safer than [ ... ])
• case ... esac for branching on patterns

Common patterns

Usage + help

usage() { echo "Usage: $0 <path> [--dry-run]" >&2; exit 2; }
[[ $# -ge 1 ]] || usage

Temporary files

tmp="$(mktemp)"
trap 'rm -f "$tmp"' EXIT

Quick checklist

• Use set -euo pipefail (and understand its implications)
• Quote expansions: "$var", "$@"
• Validate inputs early and fail fast

Related

• Shell variables and environment
• Conditionals and loops
• Debugging and optimization