Bash Cheat Sheet

Shortcuts & History

Line editing (CTRL)

• CTRL+A — move to beginning of line
• CTRL+B — move backward one character
• CTRL+C — halt the current command
• CTRL+D — delete one character backward or log out (similar to exit)
• CTRL+E — move to end of line
• CTRL+F — move forward one character
• CTRL+G — abort the current editing command and ring the terminal bell
• CTRL+H — delete one character under cursor (same as DELETE)
• CTRL+J — same as RETURN
• CTRL+K — delete (kill) forward to end of line
• CTRL+L — clear screen and redisplay the line
• CTRL+M — same as RETURN
• CTRL+O — same as RETURN, then display the next line in history file
• CTRL+P — previous line in command history
• CTRL+Q — resume suspended shell output
• CTRL+R — search backward through history
• CTRL+S — search forward, or suspend shell output
• CTRL+T — transpose two characters
• CTRL+U — kill backward from point to beginning of line
• CTRL+V — make the next character typed verbatim
• CTRL+W — kill the word behind the cursor
• CTRL+X — list possible filename completions of the current word
• CTRL+Y — retrieve (yank) last item killed
• CTRL+Z — stop the current command (resume with fg / bg)

Line editing (ALT)

• ALT+B — move backward one word
• ALT+D — delete next word
• ALT+F — move forward one word
• ALT+H — delete one character backward
• ALT+T — transpose two words
• ALT+. — paste last word from the last command (repeats through history)
• ALT+U — capitalize every character to the end of the word
• ALT+L — uncapitalize every character to the end of the word
• ALT+C — capitalize letter under cursor, cursor moves to end of word
• ALT+R — revert changes to a command pulled from history
• ALT+? — list possible completions of what is typed
• ALT+^ — expand line to most recent match from history

Key combos

• CTRL+X then (, ), E — record/recall keyboard macro
• CTRL+X then CTRL+E — invoke $EDITOR on current command line
• CTRL+A then D — log out of screen but keep process running
• BACKSPACE — delete character backward
• DELETE — delete character under cursor

History

• history — show command line history
• !! — repeat the last command
• !<n> — refer to command line n
• !<string> — refer to command starting with string
• exit — log out of current session

Bash Basics

• env — display all environment variables
• echo $SHELL — display the shell you’re using
• echo $BASH_VERSION — display bash version
• bash — start a new bash shell (type exit to return)
• whereis bash — locate the binary, source and manual-page for bash
• which bash — find which program is executed as bash
• clear — clear the terminal window

File Commands

• ls — list files in current directory (ls <dir> for another directory)
• ls -l — long format (size, owner, permissions, last modified)
• ls -a — all files including hidden (starting with .)
• ln -s <filename> <link> — create a symbolic link to a file
• readlink <filename> — show where a symbolic link points to
• tree — show directories and subdirectories in a file tree
• mc — terminal file explorer
• touch <filename> — create or update a file
• mktemp -t <filename> — make a temp file in /tmp (deleted at next boot; -d for directory)
• cat <filename> — display file raw content
• cat -n <filename> — show with line numbers
• nl <file.sh> — show number of lines
• cat f1 > f2 — copy file1 to file2
• cat f1 >> f2 — merge two files (append)
• more <filename> — page through a file
• head <filename> — first 10 lines (head -n 20 file)
• tail <filename> — last 10 lines (-f to follow)
• vim <filename> — open in VIM (creates it if missing)
• mv <file> <dest> — move/rename a file
• cp <file> <dest> — copy a file
• rm <filename> — remove a file
• find . -name <name> <type> — search files by name
• diff <f1> <f2> — compare files and show differences
• wc <filename> — lines, words, characters (-lwc for one)
• sort <filename> — sort text (alphabetical; -n numeric, -r reverse)
• sort -t -k <filename> — sort on a specific field (-t separator, -k field)
• rev — reverse string characters
• chmod -options <filename> — change read/write/execute permissions
• gzip <filename> / gunzip <filename> — compress / decompress
• gzcat <filename> — view gzipped file without decompressing
• grep <pattern> <filenames> — search for a string
• grep -r <pattern> <dir> — recursively search a directory
• head -n file | tail +n — print nth line from a file
• head -y file | tail +x — display lines x through y

sed (stream editing)

• sed 's/<p>/<r>/g' <file> — replace pattern with replacement on stdout
• sed -i 's/<p>/<r>/g' <file> — replace in place
• echo "this" | sed 's/is/at/g' — replace from input stream

Directory Commands

• mkdir <dirname> — make a new directory
• rmdir <dirname> — remove an empty directory
• rmdir -rf <dirname> — remove a non-empty directory
• mv <dir1> <dir2> — rename a directory
• cd — change to home
• cd .. — change to parent directory
• cd <dirname> — change directory
• cp -r <dir1> <dir2> — copy dir1 into dir2 including sub-directories
• pwd — print current directory
• cd ~ — change to home
• cd - — change to previous working directory

SSH, System Info & Network Commands

SSH

• ssh user@host — connect to host as user
• ssh -p <port> user@host — connect on a specified port
• ssh-copy-id user@host — add your key for passwordless login

System & user

• whoami — return your username
• su <user> — switch to a different user
• su - — switch to root
• sudo <command> — execute command as root
• passwd — change your password
• quota -v — show disk quota
• date — current date and time
• cal — show month’s calendar
• uptime — current uptime
• w — display who’s online
• finger <user> — info about user
• uname -a — kernel information
• man <command> — manual for a command
• info <command> — alternate documentation system
• help — docs about built-ins
• df — disk usage
• du <filename> — disk usage of files (-s total only)
• resize2fs — ext2/ext3/ext4 resizer
• last <user> — list last logins
• ps -u <user> — list your processes
• kill <PID> — kill process by ID
• killall <name> — kill all processes by name
• top — active processes
• lsof — list open files
• bg — list/background stopped jobs
• fg / fg <job> — bring jobs to foreground

Network

• ping <host> — ping host
• whois <domain> — whois information
• dig <domain> — DNS information
• dig -x <host> — reverse lookup
• wget <file> — download file
• netstat — network connections, routes, interface stats

Other

• time <command> — report time consumed by a command

Variables

• varname=value — define a variable
• varname=value command — variable only in the subprocess environment
• echo $varname — check a variable’s value
• echo $$ — process ID of current shell
• echo $! — process ID of most recent background job
• echo $? — exit status of last command
• read <varname> — read a string from input into a variable
• read -p "prompt" <varname> — read with a prompt
• column -t <filename> — pretty columns (often used with pipes)
• let <varname> = <equation> — math operations (+, -, *, /, %)
• export VARNAME=value — environment variable for subprocesses
• export -f <funcname> — export a function
• declare -x <varname> — copy Bash variable into environment

Arrays

array[0]=valA
array=([2]=valC [0]=valA [1]=valB)
array=(valA valB valC)

${array[i]}        # value at index i (index 0 assumed if empty)
${#array[i]}       # length of element i
${#array[@]}       # number of values in array

• declare -a — variables treated as arrays
• declare -A — associative array
• declare -i — variables treated as integers
• declare -r — read-only variables
• declare -x — marked for export
• declare -l — values converted to lowercase
• declare -f — use function names only
• declare -F — display function names without definitions

Parameter expansion (defaults & substrings)

• ${varname:-word} — return value, or word if null
• ${varname:=word} — return value, or set to word if null
• ${varname:?message} — return value, or abort with message
• ${varname:+word} — return word if not null, else null
• ${varname:offset:length} — substring from offset, up to length
• ${#varname} — length of the value

Pattern removal & replacement

• ${variable#pattern} — delete shortest match from the beginning
• ${variable##pattern} — delete longest match from the beginning
• ${variable%pattern} — delete shortest match from the end
• ${variable%%pattern} — delete longest match from the end
• ${variable/pattern/string} — replace first match
• ${variable//pattern/string} — replace all matches

Extended glob

• *(patternlist) — zero or more occurrences
• +(patternlist) — one or more occurrences
• ?(patternlist) — zero or one occurrence
• @(patternlist) — exactly one pattern
• !(patternlist) — anything except the given patterns

Command substitution

• $(UNIX command) — run the command and return its stdout

Functions

function functname() {
  shell commands
}

• unset -f functname — delete a function definition
• declare -f — display all defined functions
• Arguments are passed by position: $1, $2, … ; $@ = all args, $# = count

Flow Controls

Operators

• statement1 && statement2 — AND
• statement1 || statement2 — OR
• -a / -o — AND / OR inside a test expression

String tests

• str1 == str2 / str1 != str2 — match / no match
• str1 < str2 / str1 > str2 — alphabetical comparison
• -n str1 — not null (length > 0)
• -z str1 — null (length 0)

File tests

• -a file — file exists
• -d file — exists and is a directory
• -e file — exists (same as -a)
• -f file — exists and is a regular file
• -r file — read permission
• -s file — exists and is not empty
• -w file — write permission
• -x file — execute permission
• -N file — modified since last read
• -O file — you own the file
• -G file — group matches yours
• file1 -nt file2 — file1 is newer
• file1 -ot file2 — file1 is older

Numeric tests

• -lt less than · -le less/equal · -eq equal · -ge greater/equal · -gt greater than · -ne not equal

if / elif / else

if condition; then
  statements
elif condition; then
  statements
else
  statements
fi

for loops

for x in {1..10}; do
  statements
done

for name in list; do
  statements that can use $name
done

for (( init; condition; update )); do
  statements
done

case

case expression in
  pattern1 ) statements ;;
  pattern2 ) statements ;;
esac

select / while / until

select name in list; do
  statements that can use $name
done

while condition; do
  statements
done

until condition; do
  statements
done

Command-Line Processing Cycle

• Default lookup order: functions → built-ins → scripts/executables in PATH
• command — skip aliases/functions; only built-ins and PATH commands
• builtin — only built-in commands
• enable — enable/disable shell built-ins
• eval — run arguments through the command-line processing again

Input/Output Redirection

• cmd1|cmd2 — pipe; cmd1’s stdout to cmd2’s stdin
• < file — take stdin from file
• > file — stdout to file
• >> file — stdout to file (append)
• >|file — force output even if noclobber is set
• n>|file — force output from descriptor n
• <> file / n<>file — use file as both stdin/stdout
• n>file / n<file / n>>file — redirect descriptor n
• n>& / n<& — duplicate descriptors
• n>&m / n<&m — copy file descriptor n of m
• &>file — stdout and stderr to file
• <&- — close stdin
• >&- — close stdout
• n>&- / n<&- — close descriptor n
• cmd | tee <file> — output to both terminal and file (-a append)

Process Handling

• myCommand & — run in the background
• CTRL+Z — suspend a running job
• jobs — list jobs (-l shows PID)
• fg — bring a job to the foreground
• fg %+ / fg %- — most recent / second most recent job
• fg %N / fg %string / fg %?string — job number / command prefix / contains
• kill -l — list all signals
• kill PID — terminate process
• kill -s SIGKILL <pid> — force terminate
• kill -15 <pid> — TERM signal
• kill %1 — kill job number 1
• ps — processes of current shell; ps -a all with a tty
• trap cmd sig1 sig2 — run command on signal
• trap "" sig1 sig2 — ignore signal
• trap - sig1 sig2 — reset signal to default
• disown <PID|JID> — remove a process from the job list
• wait — wait for all background jobs to finish
• sleep <number> — wait N seconds
• pv — progress bar for data pipes
• yes — answer “yes” to every input prompt

Tips & Tricks

# alias for a frequently used host
alias gentlenode='ssh [email protected] -p 3404'

# jump to a directory by name (cdable_vars)
shopt -s cdable_vars
export websites="/Users/mac/Documents/websites"
source .bashrc
cd $websites

Debugging Shell Programs

• bash -n scriptname — syntax check only (set -o noexec in script)
• bash -v scriptname — echo commands before running (set -o verbose)
• bash -x scriptname — echo after processing (set -o xtrace)
• trap 'echo $varname' EXIT — print variables on script exit
• trap 'errtrap $LINENO' ERR — run on any non-zero exit
• trap dbgtrap DEBUG — run before every statement
• trap returntrap RETURN — run when a function/source completes
• trap - DEBUG — turn off a trap

Colors and Backgrounds

\e or \x1B work instead of \033. -e is required with echo to interpret escapes.

# Reset
Color_Off='\033[0m'          # Text Reset

# Regular Colors
Black='\033[0;30m'   Red='\033[0;31m'   Green='\033[0;32m'  Yellow='\033[0;33m'
Blue='\033[0;34m'    Purple='\033[0;35m' Cyan='\033[0;36m'  White='\033[0;97m'

# Bright variants
LGrey='\033[0;37m'   DGrey='\033[0;90m'  LRed='\033[0;91m'  LGreen='\033[0;92m'
LYellow='\033[0;93m' LBlue='\033[0;94m'  LPurple='\033[0;95m' LCyan='\033[0;96m'

# Bold
BBlack='\033[1;30m'  BRed='\033[1;31m'  BGreen='\033[1;32m' BYellow='\033[1;33m'
BBlue='\033[1;34m'   BPurple='\033[1;35m' BCyan='\033[1;36m' BWhite='\033[1;37m'

# Underline
UBlack='\033[4;30m'  URed='\033[4;31m'  UGreen='\033[4;32m' UYellow='\033[4;33m'
UBlue='\033[4;34m'   UPurple='\033[4;35m' UCyan='\033[4;36m' UWhite='\033[4;37m'

# Background
On_Black='\033[40m'  On_Red='\033[41m'  On_Green='\033[42m' On_Yellow='\033[43m'
On_Blue='\033[44m'   On_Purple='\033[45m' On_Cyan='\033[46m' On_White='\033[47m'

# Usage
echo -e "${Green}This is GREEN text${Color_Off} and normal text"
echo -e "${Red}${On_White}This is Red on White background${Color_Off}"
printf "${Red} This is red \n"