The Ultimate Bash Scripting Commands Cheat Sheet: Essential Command Reference

Introduction

This cheat sheet provides a comprehensive reference for the most useful Bash commands and operators used in shell scripting. Whether you’re writing simple automation scripts or complex system utilities, this guide will help you quickly find the right commands for your Bash scripting needs.

Essential Commands

File System Navigation & Management

Command	Description	Example
`ls`	List directory contents	`ls -la` (all files with details)
`cd`	Change directory	`cd /path/to/dir`
`pwd`	Print working directory	`pwd`
`mkdir`	Create directory	`mkdir -p parent/child` (with parents)
`rm`	Remove files/directories	`rm -rf dir` (recursive, force)
`cp`	Copy files/directories	`cp -R source/ dest/` (recursive)
`mv`	Move/rename files	`mv oldname newname`
`touch`	Create empty file/update timestamp	`touch file.txt`
`find`	Search for files	`find . -name "*.txt"`
`locate`	Find files by name (using database)	`locate filename`
`chmod`	Change file permissions	`chmod 755 script.sh`
`chown`	Change file owner	`chown user:group file`

Text Processing

Command	Description	Example
`cat`	Display file contents	`cat file.txt`
`less`	View file with pagination	`less large_file.log`
`head`	Show first lines of file	`head -n 10 file.txt`
`tail`	Show last lines of file	`tail -f log.txt` (follow updates)
`grep`	Search text for patterns	`grep -i "error" log.txt` (case insensitive)
`sed`	Stream editor for text transformation	`sed 's/old/new/g' file.txt`
`awk`	Pattern scanning and processing	`awk '{print $1}' file.txt` (print first column)
`sort`	Sort lines of text	`sort -n numbers.txt` (numeric sort)
`uniq`	Report or filter out repeated lines	`sort file.txt \| uniq -c` (count occurrences)
`wc`	Count lines, words, characters	`wc -l file.txt` (line count)
`cut`	Remove sections from lines	`cut -d',' -f1,3 data.csv` (fields 1 & 3)
`tr`	Translate or delete characters	`echo "Hello" \| tr 'a-z' 'A-Z'` (uppercase)

System Information & Management

Command	Description	Example
`ps`	Report process status	`ps aux` (all processes)
`top`	Display running processes	`top`
`htop`	Interactive process viewer	`htop`
`df`	Report disk space usage	`df -h` (human-readable)
`du`	Estimate file space usage	`du -sh directory` (summary, human-readable)
`free`	Display memory usage	`free -m` (in megabytes)
`uname`	Print system information	`uname -a` (all info)
`hostname`	System hostname	`hostname`
`whoami`	Current username	`whoami`
`uptime`	System uptime	`uptime`
`which`	Show full path of commands	`which bash`
`date`	Display or set date/time	`date +"%Y-%m-%d"` (formatted)

Network Operations

Command	Description	Example
`ping`	Test network connectivity	`ping -c 4 google.com` (4 packets)
`curl`	Transfer data from/to servers	`curl -O https://example.com/file.zip` (download)
`wget`	Non-interactive downloader	`wget -q https://example.com/file` (quiet)
`ssh`	Secure shell client	`ssh user@hostname`
`scp`	Secure copy	`scp file.txt user@host:/path/`
`rsync`	Fast, versatile file copying	`rsync -avz source/ dest/`
`netstat`	Network statistics	`netstat -tuln` (TCP/UDP listening)
`ifconfig`	Network interface config	`ifconfig eth0`
`ip`	IP configuration (modern)	`ip addr show`
`host`	DNS lookup	`host example.com`
`dig`	DNS lookup (detailed)	`dig example.com`
`nslookup`	Query DNS records	`nslookup example.com`

File Compression & Archiving

Command	Description	Example
`tar`	Tape archive	`tar -czvf archive.tar.gz directory/` (create)
		`tar -xzvf archive.tar.gz` (extract)
`zip`	Create ZIP archive	`zip -r archive.zip directory/`
`unzip`	Extract ZIP archive	`unzip archive.zip`
`gzip`	Compress files	`gzip file.txt`
`gunzip`	Uncompress gzip files	`gunzip file.txt.gz`

Command Chaining & Control Operators

Command Connectors

Operator	Description	Example
`;`	Run commands sequentially	`cmd1 ; cmd2` (both run regardless)
`&&`	Logical AND	`cmd1 && cmd2` (cmd2 runs if cmd1 succeeds)
`\|\|`	Logical OR	`cmd1 \|\| cmd2` (cmd2 runs if cmd1 fails)
`&`	Background execution	`cmd &` (run in background)
`\|`	Pipe output to input	`cmd1 \| cmd2` (cmd1 output to cmd2 input)
`!`	Negate a command	`! grep pattern file` (true if pattern not found)

IO Redirection

Operator	Description	Example
`>`	Redirect stdout (overwrite)	`cmd > file.txt`
`>>`	Redirect stdout (append)	`cmd >> file.txt`
`2>`	Redirect stderr	`cmd 2> errors.log`
`2>&1`	Redirect stderr to stdout	`cmd > output.txt 2>&1`
`&>`	Redirect both stdout and stderr	`cmd &> all_output.txt`
`<`	Input from file	`cmd < input.txt`
`<<`	Here document	`cat << EOF ... EOF`
`<<<`	Here string	`grep pattern <<< "string to search"`
`/dev/null`	Discard output	`cmd > /dev/null`

Bash Expansions & Substitutions

Parameter Expansion

Syntax	Description	Example
`${var}`	Basic variable expansion	`echo ${name}`
`${var:-default}`	Use default if var unset/null	`echo ${name:-"John"}`
`${var:=default}`	Set default if var unset/null	`${count:=0}`
`${var:+value}`	Use value if var set, else nothing	`${name:+"Hello, $name"}`
`${var:?error}`	Error if var unset/null	`${required:?"Missing value"}`
`${var:offset}`	Substring from offset	`${str:7}`
`${var:offset:length}`	Substring with length	`${str:7:3}`
`${#var}`	String length	`echo ${#name}`
`${var#pattern}`	Remove shortest match from start	`${path#*/}`
`${var##pattern}`	Remove longest match from start	`${path##*/}`
`${var%pattern}`	Remove shortest match from end	`${file%.*}`
`${var%%pattern}`	Remove longest match from end	`${file%%.*}`
`${var/pattern/replacement}`	Replace first match	`${text/foo/bar}`
`${var//pattern/replacement}`	Replace all matches	`${text//foo/bar}`
`${var^}`	Uppercase first character	`${name^}`
`${var^^}`	Uppercase all characters	`${name^^}`
`${var,}`	Lowercase first character	`${name,}`
`${var,,}`	Lowercase all characters	`${name,,}`

Brace Expansion

Syntax	Description	Example
`{x,y,z}`	Expand to x y z	`echo file.{txt,html,pdf}`
`{start..end}`	Range expansion	`echo {1..5}`
`{start..end..step}`	Range with step	`echo {1..10..2}`

Command Substitution

Syntax	Description	Example
`$(command)`	Execute command, substitute output	`files=$(ls -la)`
`command`	Legacy syntax for command substitution	today=`date`

Conditional Expressions

File Test Operators

Operator	Description	Example
`-e file`	File exists	`[ -e /etc/passwd ]`
`-f file`	Regular file	`[ -f "$script" ]`
`-d file`	Directory	`[ -d "$dir" ]`
`-h file`	Symbolic link	`[ -h "$link" ]`
`-r file`	Readable	`[ -r "$file" ]`
`-w file`	Writable	`[ -w "$file" ]`
`-x file`	Executable	`[ -x "$command" ]`
`-s file`	Non-zero size	`[ -s "$file" ]`
`-N file`	Modified since last read	`[ -N "$file" ]`
`file1 -nt file2`	Newer than	`[ "$file1" -nt "$file2" ]`
`file1 -ot file2`	Older than	`[ "$file1" -ot "$file2" ]`

String Test Operators

Operator	Description	Example
`-z string`	Empty string	`[ -z "$var" ]`
`-n string`	Non-empty string	`[ -n "$var" ]`
`str1 = str2`	Equal	`[ "$a" = "$b" ]`
`str1 != str2`	Not equal	`[ "$a" != "$b" ]`
`str1 < str2`	Less than (ASCII)	`[[ "$a" < "$b" ]]`
`str1 > str2`	Greater than (ASCII)	`[[ "$a" > "$b" ]]`
`=~`	Regex match (in `[[]]`)	`[[ "$email" =~ ^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$ ]]`

Numeric Comparison Operators

Operator	Description	Example
`-eq`	Equal	`[ "$a" -eq "$b" ]`
`-ne`	Not equal	`[ "$a" -ne "$b" ]`
`-lt`	Less than	`[ "$a" -lt "$b" ]`
`-le`	Less than or equal	`[ "$a" -le "$b" ]`
`-gt`	Greater than	`[ "$a" -gt "$b" ]`
`-ge`	Greater than or equal	`[ "$a" -ge "$b" ]`

Logical Operators

Operator	Description	Example
`!`	Logical NOT	`[ ! -f "$file" ]`
`-a`	Logical AND (in test)	`[ "$a" -gt 0 -a "$a" -lt 10 ]`
`-o`	Logical OR (in test)	`[ "$a" -lt 0 -o "$a" -gt 100 ]`
`&&`	Logical AND (between tests)	`[ "$a" -gt 0 ] && [ "$a" -lt 10 ]`
`\|\|`	Logical OR (between tests)	`[ "$a" -lt 0 ] \|\| [ "$a" -gt 100 ]`

Special Built-in Commands

Command	Description	Example
`echo`	Display text	`echo "Hello, World!"`
`printf`	Formatted output	`printf "Name: %s\n" "$name"`
`read`	Read user input	`read -p "Enter name: " name`
`eval`	Execute arguments as command	`eval "ls $options"`
`source`	Execute commands from file	`source ~/.bashrc`
`.`	Same as source	`. script.sh`
`set`	Set/unset shell options	`set -e` (exit on error)
`unset`	Remove variable/function	`unset var_name`
`export`	Set environment variable	`export PATH=$PATH:/new/dir`
`let`	Arithmetic evaluation	`let "count = $count + 1"`
`declare`	Declare variables with attributes	`declare -i number=10` (integer)
`readonly`	Make variables read-only	`readonly API_KEY="abc123"`
`shift`	Shift positional parameters	`shift` or `shift 2`
`wait`	Wait for process completion	`wait $pid`
`trap`	Execute command on signal	`trap "echo 'Exiting...'" EXIT`
`exec`	Replace current process	`exec new_command`
`exit`	Exit with status code	`exit 0`
`return`	Exit function with status	`return 1`
`getopts`	Parse command options	`while getopts "a:b:" opt; do ...`

Process Management Commands

Command	Description	Example
`jobs`	List active jobs	`jobs -l` (with PID)
`fg`	Bring job to foreground	`fg %1` (job number 1)
`bg`	Resume job in background	`bg %2`
`kill`	Send signal to process	`kill -9 $pid` (SIGKILL)
`pkill`	Signal processes by name	`pkill -f "process_name"`
`killall`	Kill processes by name	`killall httpd`
`nohup`	Run command immune to hangups	`nohup long_process &`
`nice`	Run with modified priority	`nice -n 10 command`
`renice`	Alter priority of running process	`renice +10 -p $pid`
`time`	Time command execution	`time command`
`timeout`	Run command with time limit	`timeout 5s command`
`watch`	Periodically execute command	`watch -n 5 'ls -la'`
`crontab`	Schedule periodic jobs	`crontab -e` (edit)
`at`	Schedule one-time job	`at 10:00 < script.sh`

Advanced Commands & Utilities

Command	Description	Example
`xargs`	Build command lines from stdin	`find . -name "*.log" \| xargs rm`
`tee`	Read from stdin and write to stdout/files	`command \| tee output.txt`
`bc`	Precision calculator	`echo "scale=2; 5/2" \| bc`
`jq`	JSON processor	`curl api.com/data \| jq '.results'`
`awk`	Pattern scanning and processing	`awk -F, '{print $1 " " $3}' file.csv`
`sed`	Stream editor	`sed -i 's/old/new/g' file.txt`
`envsubst`	Substitute environment variables	`envsubst < template.txt > output.txt`
`parallel`	Execute commands in parallel	`ls *.jpg \| parallel convert {} {.}.png`
`comm`	Compare sorted files	`comm -12 file1 file2` (common lines)
`diff`	Compare files line by line	`diff -u file1 file2`
`patch`	Apply diff file	`patch < patchfile`
`split`	Split files into pieces	`split -b 1G large_file prefix_`
`csplit`	Split files by context	`csplit file '/^##/' {*}`
`join`	Join lines on a common field	`join file1 file2`
`column`	Format output in columns	`ls -l \| column -t`
`fmt`	Simple text formatter	`fmt -w 80 file.txt`
`nl`	Number lines	`nl -ba file.txt`
`seq`	Generate sequence of numbers	`seq 1 5`
`shuf`	Generate random permutations	`shuf -n 5 file.txt`
`logger`	Log to system log	`logger "Backup completed"`

Special Variables & Aliases

Helpful Environment Variables

Variable	Description
`PATH`	Executable search path
`HOME`	User’s home directory
`USER`	Current username
`HOSTNAME`	System hostname
`PWD`	Current working directory
`OLDPWD`	Previous working directory
`SHELL`	Path to current shell
`LANG`	System language/locale
`TERM`	Terminal type
`PS1`	Primary prompt string
`PS2`	Secondary prompt string
`IFS`	Internal field separator
`CDPATH`	Search path for cd command
`EDITOR`	Default text editor

Useful Aliases (Add to .bashrc)

# Navigation
alias ll='ls -la'
alias la='ls -a'
alias l='ls -CF'
alias ..='cd ..'
alias ...='cd ../..'

# Safety
alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'

# Shortcuts
alias c='clear'
alias h='history'
alias j='jobs -l'

# System info
alias meminfo='free -m -l -t'
alias cpuinfo='lscpu'
alias diskinfo='df -h'

# Network
alias ports='netstat -tulanp'
alias myip='curl http://ipecho.net/plain; echo'

Resources for Further Learning

Official Documentation

GNU Bash Reference Manual: https://www.gnu.org/software/bash/manual/
Man pages: man bash, man test

Online Resources

Bash Guide for Beginners: https://tldp.org/LDP/Bash-Beginners-Guide/html/
Explainshell.com (command explanations)
ShellCheck (script analysis tool)

This cheat sheet provides a comprehensive reference for Bash scripting commands. Remember that many commands have additional options and functionalities not covered here—check their man pages (man command) for complete documentation.