Bash Cheat Sheet

This Bash cheat sheet covers everything you need to work efficiently in the terminal, from basic navigation to advanced scripting patterns.

Bash is the default shell on Linux and most Unix-based systems. It's also a full scripting language. Knowing it well saves you hours.

What's Inside

• Basics - navigation, environment variables, history, and help commands

• Files & Directories - create, delete, copy, move, find, and inspect files

• Text & Search - grep, sed, awk, xargs, pipes, and redirection

• Processes - manage running processes, background jobs, and signals

• Scripting - variables, arrays, loops, functions, conditionals, here-docs, trap, and cron

• Network - curl, SSH, SCP, rsync, and diagnostics

• Permissions - chmod, chown, and sudo patterns

• Archive - tar, gzip, zip, and extraction commands

• Shortcuts - keyboard shortcuts and useful one-liners

Who It's For

Developers, sysadmins, and DevOps engineers who work in the terminal daily. Also useful for anyone writing automation scripts or managing servers.

Every snippet is copy-ready. Most include a preview showing expected output or behavior. Compatibility badges mark which commands are POSIX-safe, GNU-specific, or require bash 4+.

Strict mode, signal handling, regex matching, associative arrays -- the parts that trip people up are all here, with working examples.

What is Bash

Bash is the Bourne-Again SHell, a Unix shell and command language that ships as the default login shell on most Linux distributions.

It works as both an interactive command-line interface and a scripting engine for automating tasks on Linux and Unix systems.

Developed by Brian Fox for the GNU Project in 1989, Bash replaced the original Bourne Shell (sh) while staying backward compatible with POSIX standards.

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How Does Bash Differ from Other Shells

Bash supports arrays, arithmetic expansion, and command history out of the box - features sh lacks.

Zsh adds smarter tab completion and plugin ecosystems (Oh My Zsh).

Fish prioritizes user-friendliness with syntax highlighting and autosuggestions, but breaks POSIX compatibility.

Bash stays the safest choice for cross-platform shell scripting across Linux, macOS, and Windows Subsystem for Linux (WSL).

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Bash Syntax

What is the Bash Shebang Line

#!/bin/bash goes on the very first line of any bash script.

It tells the OS to use the bash interpreter, not whatever shell the current user runs.

Without it, the script may execute under sh or another shell, breaking bash-specific syntax.

What Are Bash Comments

Single-line comments start with #.

Multi-line comments use the : '...' workaround - not a true comment block, but widely used in bash shell scripting.

How Do Bash Quoting Rules Work

• Single quotes '...' - literal string, no expansion

• Double quotes "..." - allows $variable and command substitution

• Backticks cmd - command substitution (prefer $(cmd) instead)

• Backslash \ - escapes single characters

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Bash Variables

How Do You Declare and Use Variables in Bash

NAME="John"
echo "$NAME"     # John
echo "${NAME}!"  # John!
NAME = "John"    # Error - no spaces around =

Always quote variables: "$NAME" prevents word splitting and glob expansion.

Variable Types in Bash

• Local variables - exist only in the current shell session

• Environment variables - exported with export VAR=value, inherited by child processes

• Special variables - $0 (script name), $1–$9 (positional args), $# (arg count), $@ (all args), $? (last exit code), $$ (current PID)

• Read-only variables - set with readonly VAR=value

How Does String Manipulation Work in Bash

Bash handles string operations directly through parameter expansion - no external tools needed for basic tasks.

Operation	Syntax	Result
Length	${#var}	character count
Substring	${var:2:4}	chars at offset 2, length 4
Replace first	${var/old/new}	one substitution
Replace all	${var//old/new}	all matches
Strip prefix	${var#prefix}	removes shortest match
Strip suffix	${var%suffix}	removes shortest match
Uppercase	${var^^}	all caps
Lowercase	${var,,}	all lowercase

What Are Bash Arrays

# Indexed array
fruits=("apple" "banana" "cherry")
echo "${fruits[0]}"    # apple
echo "${fruits[@]}"    # all elements
echo "${#fruits[@]}"   # array length

# Associative array
declare -A colors
colors["red"]="#FF0000"
echo "${colors["red"]}"

Iterate with for item in "${fruits[@]}".

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Bash Operators

What Are Bash Arithmetic Operators

Use $(( )) for integer math - no external tools required.

echo $((5 + 3))    # 8
echo $((10 % 3))   # 1
echo $((2 ** 8))   # 256

let and expr work too, but $(( )) is faster and cleaner.

What Are Bash Comparison Operators

[ ] is POSIX-compatible.

[[ ]] is bash-specific - safer, supports regex with =~, no need to quote variables.

Integer Comparison Operators Table

Operator	Meaning
-eq	equal to
-ne	not equal to
-lt	less than
-gt	greater than
-le	less than or equal
-ge	greater than or equal

String Comparison Operators Table

Operator	Meaning
= or ==	strings are equal
!=	strings are not equal
-z	string is empty
-n	string is not empty

What Are Bash File Test Operators

File tests go inside [ ] or [[ ]].

Operator	True when
-f file	file exists and is a regular file
-d file	directory exists
-r file	readable
-w file	writable
-x file	executable
-s file	file exists and size > 0
-e file	exists (any type)

if [[ -f "/etc/hosts" ]]; then
  echo "File exists"
fi

Bash Control Flow

How Do If Statements Work in Bash

if [[ "$name" == "John" ]]; then
  echo "Hello John"
elif [[ "$name" == "Jane" ]]; then
  echo "Hello Jane"
else
  echo "Who are you?"
fi

Use && and || for inline conditionals: [[ -f file ]] && echo "exists".

How Do For Loops Work in Bash

# List iteration
for fruit in apple banana cherry; do
  echo "$fruit"
done

# Range
for i in {1..5}; do echo "$i"; done

# C-style
for ((i=0; i<10; i++)); do echo "$i"; done

# Array
for item in "${arr[@]}"; do echo "$item"; done

How Do While and Until Loops Work in Bash

count=0
while [[ $count -lt 5 ]]; do
  echo "$count"
  ((count++))
done

until runs while the condition is false - the inverse of while.

Use break to exit a loop early; continue to skip to the next iteration.

How Does a Case Statement Work in Bash

case "$1" in
  start | up)
    echo "Starting..."
    ;;
  stop | down)
    echo "Stopping..."
    ;;
  *)
    echo "Usage: $0 {start|stop}"
    ;;
esac

Cleaner than chained if/elif blocks when matching one variable against multiple patterns.

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Bash Functions

How Do You Define and Call Functions in Bash

greet() {
  echo "Hello, $1"
}

greet "World"    # Hello, World

Both function greet { } and greet() { } syntax work.

Parameters use $1, $2, etc. - no argument declaration needed.

How Do You Return Values from Bash Functions

return only exits with a status code (0–255) - not a value.

To capture actual output, use command substitution:

get_name() { echo "John"; }
name=$(get_name)
echo "$name"    # John

Check exit status with $? after any function call.

What is Variable Scope in Bash Functions

All variables are global by default - even ones set inside functions.

Use local to restrict scope:

myfunc() {
  local x=10
  echo "$x"
}
# $x is unavailable here

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Bash Input and Output

How Do Bash Redirections Work

Syntax	Action
cmd > file	overwrite file with stdout
cmd >> file	append stdout to file
cmd < file	read stdin from file
cmd 2> file	redirect stderr
cmd 2>&1	merge stderr into stdout
cmd > /dev/null	discard output

What is Piping in Bash

| passes the stdout of one command as stdin to the next.

ls -la | grep ".sh" | wc -l

Pipes chain commands; redirections connect commands to files.

How Does Here Document (Heredoc) Work in Bash

cat <<EOF
Line one
Line two
EOF

Use <<-EOF to allow indented content.

Heredocs pass multi-line input to commands - useful for generating config files or SQL queries inside scripts.

What is Process Substitution in Bash

diff <(ls dir1) <(ls dir2)

<(command) treats command output as a temporary file.

Works where a filename is expected but you only have command output - can't be piped.

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Bash File and Directory Commands

What Are the Core Bash File Management Commands

Command	Purpose
ls -la	list all files with permissions
cp -r src/ dst/	copy directory recursively
mv file.txt /path/	move or rename
rm -rf dir/	delete directory (no undo)
mkdir -p a/b/c	create nested directories
touch file.txt	create empty file or update timestamp
find . -name "*.sh"	find files by name pattern
chmod +x script.sh	make file executable

How Do You Search File Contents in Bash

grep -rn "search_term" ./          # recursive, with line numbers
grep -i "pattern" file.txt         # case-insensitive
grep -v "exclude" file.txt         # invert match

sed handles find-and-replace in files; awk extracts and processes columns.

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Bash Process Management

How Do You Manage Processes in Bash

ps aux                 # list all processes
kill 1234              # terminate PID 1234
kill -9 1234           # force kill
nohup ./script.sh &    # run after logout

Find a PID with ps aux | grep process_name or pgrep process_name.

What Are Background and Foreground Jobs in Bash

./script.sh &      # run in background
jobs               # list background jobs
fg %1              # bring job 1 to foreground
bg %1              # resume job 1 in background

Ctrl+Z suspends the current foreground process; Ctrl+C terminates it.

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Bash Scripting Patterns

How Do You Handle Script Arguments in Bash

echo "Script: $0"
echo "First arg: $1"
echo "All args: $@"
echo "Arg count: $#"

shift removes $1 and shifts remaining args down.

For flag parsing, use getopts:

while getopts "f:v" opt; do
  case $opt in
    f) file="$OPTARG" ;;
    v) verbose=true ;;
  esac
done

How Do You Handle Errors in Bash Scripts

set -e           # exit on any error
set -u           # error on undefined variables
set -o pipefail  # catch errors in pipes
set -euo pipefail  # all three together (common pattern)

Add a trap for cleanup on errors:

trap 'echo "Error on line $LINENO"' ERR

How Do You Debug a Bash Script

bash -n script.sh    # syntax check only
bash -x script.sh    # trace execution
set -x               # enable trace inside script
set +x               # disable trace

ShellCheck catches bugs statically before you run anything - use it.

What is the Difference Between [ ] and [[ ]] in Bash

[ ] is POSIX-portable but fragile - unquoted variables cause word splitting.

[[ ]] is bash-specific, supports regex matching with =~, handles empty variables safely, and is the right choice for any bash script.

[[ "$str" =~ ^[0-9]+$ ]] && echo "numeric"

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Bash Keyboard Shortcuts

What Are the Most Useful Bash Keyboard Shortcuts

Learn these and you'll move through the terminal twice as fast.

Ctrl+R reverse-searches your bash command history.

Ctrl+L clears the screen without wiping history; Ctrl+C kills the current process; Ctrl+D closes the session.

Navigation Shortcuts

Shortcut	Action
Ctrl+A	move to start of line
Ctrl+E	move to end of line
Alt+F	move forward one word
Alt+B	move backward one word

Editing Shortcuts

Shortcut	Action
Ctrl+U	cut from cursor to line start
Ctrl+K	cut from cursor to line end
Ctrl+W	cut previous word
Ctrl+Y	paste (yank) cut text

History Shortcuts

Shortcut	Action
Ctrl+R	reverse search history
!!	repeat last command
!$	last argument of previous command
!n	run command number n from history

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Bash Configuration Files

What Are Bash Configuration Files

File	Loaded when
~/.bashrc	interactive non-login shell (new terminal tab)
~/.bash_profile	login shell (SSH, first login)
~/.bash_logout	on logout
~/.bash_history	stores command history

Most desktop terminals load ~/.bashrc.

SSH sessions load ~/.bash_profile - a common source of "my alias works locally but not on the server" confusion.

How Do You Create Bash Aliases

alias ll='ls -la'
alias gs='git status'
alias ..='cd ..'

Add aliases to ~/.bashrc for persistence.

unalias ll removes one; unalias -a removes all.

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Bash String Operations

How Do You Perform String Operations in Bash

str="Hello World"
echo "${#str}"           # 11 (length)
echo "${str^^}"          # HELLO WORLD
echo "${str,,}"          # hello world
echo "${str/World/Bash}" # Hello Bash
[[ "$str" == *"World"* ]] && echo "contains World"

Split a string by setting IFS:

IFS=',' read -ra parts <<< "a,b,c"
echo "${parts[0]}"    # a

String Manipulation Reference

Operation	Syntax	Result
Length	${#var}	character count
Substring	${var:2:3}	3 chars from offset 2
Replace first	${var/old/new}	one substitution
Replace all	${var//old/new}	all matches
Strip prefix	${var#prefix}	removes shortest match
Strip suffix	${var%suffix}	removes shortest match

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Bash Conditional Expressions

What Are Bash Logical Operators

Inside [[ ]]: use && (AND), || (OR), ! (NOT).

[[ -f file && -r file ]] && echo "readable file"
[[ ! -d dir ]] && mkdir dir

Between commands: cmd1 && cmd2 runs cmd2 only if cmd1 succeeds; cmd1 || cmd2 runs cmd2 only if cmd1 fails.

How Does Brace Expansion Work in Bash

echo {a,b,c}.txt          # a.txt b.txt c.txt
mkdir project/{src,tests,docs}
echo {1..5}               # 1 2 3 4 5
echo {a..z}               # a b c d ... z
cp config.yaml{,.bak}     # quick backup trick

Brace expansion runs before any other expansion - no files need to exist.

Works inside for loops, mkdir, cp, mv, and anywhere a list of values is needed.

FAQ on Bash Cheat Sheets

What is a bash cheat sheet used for?

A bash cheat sheet is a quick reference for bash shell commands, syntax, and scripting patterns.

It saves time by keeping the most-used commands - file operations, loops, conditionals, redirections - in one scannable place instead of digging through man pages.

What are the most important bash commands to know?

ls, cd, cp, mv, rm, find, grep, chmod, and echo cover most daily Linux terminal work.

For bash scripting, add if, for, while, case, and function syntax to that list.

What is the difference between bash and shell scripting?

Shell scripting is the broad concept - writing scripts for any Unix shell.

Bash scripting is shell scripting specifically using the Bourne-Again SHell, which adds arrays, arithmetic expansion, and [[ ]] conditionals beyond basic POSIX sh.

How do I run a bash script?

Make it executable with chmod +x script.sh, then run it with ./script.sh.

Alternatively, call it directly with bash script.sh - no execute permission needed. Always start scripts with the #!/bin/bash shebang line.

What does $? mean in bash?

$? holds the exit code of the last executed command.

0 means success; any non-zero value means failure. Scripts commonly check $? after commands to decide whether to continue or trigger error handling.

What is the difference between single and double quotes in bash?

Single quotes preserve every character literally - no variable expansion, no special characters processed.

Double quotes allow $variable substitution and command substitution with $(), but still protect spaces and most special characters from the shell.

How do I debug a bash script?

Run bash -x script.sh to trace each command as it executes.

Add set -euo pipefail at the top of any script to catch errors, undefined variables, and failed pipes early. Tools like ShellCheck catch syntax issues before runtime.

What are bash special variables?

Special variables include $0 (script name), $1–$9 (positional arguments), $# (argument count), $@ (all arguments), $$ (current process ID), and $! (last background process ID).

These are read-only and set automatically by the shell.

How do I loop through files in bash?

Use a for loop with glob expansion:

for file in *.txt; do
  echo "$file"
done

Always quote "$file" inside the loop to handle filenames with spaces correctly. Works across all Linux distributions without extra tools.

What is the safest way to write bash scripts?

Start every script with set -euo pipefail - exits on errors, catches undefined variables, and prevents silent pipe failures.

Use [[ ]] instead of [ ], quote all variables, and run scripts through ShellCheck before deploying to any production environment.