Bash Shell Scripting Cheat Sheet — Syntax, Conditionals & Loops

Practical syntax reference for Bash scripts, conditional flags (-f, -d, -z), loops, variables, exit codes, and string manipulation.

Script Headers & Conditionals

#!/usr/bin/env bash
set -euo pipefail

Strict Bash header: exits immediately on error, unset variable, or failed pipeline

if [[ -f "$FILE" ]]; then ... fi

Check if file exists and is a regular file

if [[ -z "$VAR" ]]; then ... fi

Check if string variable is empty or unset (-n checks non-empty)

if [[ "$EXIT_CODE" -eq 0 ]]; then

Numeric comparison: -eq (equal), -ne (not equal), -gt (greater), -lt (less)

$? / $# / $@

$? = exit code of last command, $# = arg count, $@ = all arguments array

for file in *.png; do ... done

Iterate over file glob matches in current directory

OUTPUT=$(curl -s https://api.example.com)

Command substitution: capture command stdout into variable