---
title: "Bash Scripting Cheatsheet | FindUtils"
description: "Variables, loops, conditionals, functions, and scripting patterns for Bash shell"
url: https://findutils.com/cheatsheets/bash-scripting/
---

# Bash Scripting Cheatsheet

Variables, loops, conditionals, functions, and scripting patterns for Bash shell 53 commands in 7 sections, filed under [Linux & Terminal](https://findutils.com/cheatsheets/linux/).

## Variables & Strings

- `NAME="value"`: Assign variable (no spaces around =)
- `$NAME or ${NAME}`: Reference variable
- `"Hello $NAME"`: String with variable interpolation
- `'Hello $NAME'`: Literal string (no interpolation)
- `${#STR}`: String length
- `${STR:0:5}`: Substring (offset:length)
- `${STR/old/new}`: Replace first occurrence
- `${STR//old/new}`: Replace all occurrences
- `${STR^^}`: Uppercase entire string
- `${STR,,}`: Lowercase entire string

## Conditionals

- `if [ condition ]; then ... fi`: Basic if statement
- `if [[ $a == $b ]]; then ...`: Extended test (preferred)
- `-eq  -ne  -lt  -gt  -le  -ge`: Numeric comparisons
- `==  !=`: String comparisons (inside [[ ]])
- `-z "$STR"`: True if string is empty
- `-n "$STR"`: True if string is non-empty
- `-f <file>`: True if file exists and is regular
- `-d <dir>`: True if directory exists
- `-e <path>`: True if path exists (file or dir)
- `&&  ||`: Logical AND / OR

## Loops

- `for i in 1 2 3; do ... done`: For loop over list
- `for i in {1..10}; do ... done`: For loop with range
- `for f in *.txt; do ... done`: For loop over files (glob)
- `for ((i=0; i<10; i++)); do ...`: C-style for loop
- `while [ condition ]; do ... done`: While loop
- `while read -r line; do ... done < file`: Read file line by line
- `break`: Exit loop
- `continue`: Skip to next iteration

## Functions

- `function name() { ... }`: Define a function
- `name() { ... }`: Define function (shorthand)
- `$1 $2 $3`: Function arguments (positional)
- `$#`: Number of arguments
- `$@`: All arguments as separate words
- `$?`: Exit status of last command
- `return <n>`: Return exit code from function
- `local var="value"`: Local variable in function

## Input/Output & Redirection

- `echo "text"`: Print text to stdout
- `printf "%s\n" "text"`: Formatted output
- `read -p "Prompt: " VAR`: Read user input into variable
- `cmd > file`: Redirect stdout to file (overwrite)
- `cmd >> file`: Redirect stdout to file (append)
- `cmd 2> file`: Redirect stderr to file
- `cmd &> file`: Redirect both stdout and stderr
- `cmd1 | cmd2`: Pipe stdout of cmd1 to cmd2
- `cmd < file`: Redirect file as stdin

## Special Variables

- `$0`: Script name
- `$$`: Current process ID (PID)
- `$!`: PID of last background process
- `$?`: Exit status of last command
- `$_`: Last argument of previous command
- `RANDOM`: Random number (0-32767)
- `SECONDS`: Seconds since script started

## Sources

- `https://www.gnu.org/software/bash/manual/`: GNU Bash: variables, expansion, conditions, loops, functions, and redirection.

## Related

- Cheatsheet: [Linux Commands](https://findutils.com/cheatsheets/linux-commands/)
- Cheatsheet: [Vim Editor](https://findutils.com/cheatsheets/vim-editor/)
- Cheatsheet: [SSH Commands](https://findutils.com/cheatsheets/ssh-commands/)
- Guide: [JSON to PDF Guide: Build Documents and Check Export Limits](https://findutils.com/guides/json-to-pdf-renderer-guide/)