- Published on
Bash Cheat Sheet 2023 - Master Bash Scripting
Table of content
Bash: CheetSheet
What is Bash ?
Bash is a powerful programming language, one perfectly designed for use on the command line and in shell scripts. Bash can be used to automate software development tasks such as code compilation, debugging source code, change management and software testing.
In this article we will discuss about common Bash Commands and their usase-
Bash Shortcut Commands
Command | Explanation |
---|---|
CTRL+A | Move to beginning of line |
CTRL+B | Moves backward one character |
CTRL+C | Halts the current command |
CTRL+D | Deletes one character backward or logs out of current session, similar to exit |
CTRL+E | Moves to end of line |
CTRL+F | Moves forward one character |
CTRL+G | Aborts the current editing command and ring the terminal bell |
CTRL+H | Deletes one character under cursor (same as DELETE) |
CTRL+J | Same as RETURN |
CTRL+K | Deletes (kill) forward to end of line |
CTRL+L | Clears screen and redisplay the line |
CTRL+M | Same as RETURN |
CTRL+N | Next line in command history |
CTRL+O | Same as RETURN, then displays next line in history file |
CTRL+P | Previous line in command history |
CTRL+Q | Resumes suspended shell output |
CTRL+R | Searches backward |
CTRL+S | Searches forward or suspends shell output |
CTRL+T | Transposes two characters |
CTRL+U | Kills backward from point to the beginning of line |
CTRL+V | Makes the next character typed verbatim |
CTRL+W | Kills the word behind the cursor |
CTRL+X | Lists the possible filename completions of the current word |
CTRL+Y | Retrieves (yank) last item killed |
CTRL+Z | Stops the current command, resume with fg in the foreground or bg in the background |
ALT+B | Moves backward one word |
ALT+D | Deletes next word |
ALT+F | Moves forward one word |
ALT+H | Deletes one character backwar |
ALT+T | Transposes two words |
ALT+. | Pastes last word from the last command. Pressing it repeatedly traverses through command history. |
ALT+U | Capitalizes every character from the current cursor position to the end of the word |
ALT+L | Uncapitalizes every character from the current cursor position to the end of the word |
ALT+C | Capitalizes the letter under the cursor. The cursor then moves to the end of the word. |
ALT+R | Reverts any changes to a command you’ve pulled from your history if you’ve edited it. |
ALT+? | List possible completions to what is typed |
ALT+^ | Expand line to most recent match from history |
CTRL+X then ( | Start recording a keyboard macro |
CTRL+X then ) | Finish recording keyboard macro |
CTRL+X then E | Recall last recorded keyboard macro |
CTRL+X then CTRL+E | Invoke text editor (specified by $EDITOR) on current command line then execute resultes as shell commands |
CTRL+A then D | Logout from screen but don't kill it, if any command exist, it will continue |
BACKSPACE | Deletes one character backward |
DELETE | Deletes one character under cursor |
history | Shows command line history |
!! | Repeats the last command |
!<n> | Refers to command line n |
!<string> | Refers to command starting with string |
esc :wq | Exits and saves script |
exit | Logs out of current session |
BASH Basic Commands
Command | Explanation |
---|---|
env | Displays all environment variables |
echo $SHELL | Displays the shell you're using |
echo $BASH_VERSION | Displays bash version |
bash | If you want to use bash (type exit to go back to your previously opened shell) |
whereis bash | Locates the binary, source and manual-page for a command |
which bash | Finds out which program is executed as 'bash' (default: /bin/bash, can change across environments) |
clear | Clears content on window (hide displayed lines) |
BASH FILE COMMANDS
Command | Explanation |
---|---|
ls | Lists your files in current directory, ls <dir> to print files in a specific directory |
ls -l | Lists your files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified |
ls -a | Lists all files in 'long format', including hidden files (name beginning with '.') |
ln -s <filename> <link> | Creates symbolic link to file |
readlink <filename> | Shows where a symbolic links points to |
tree | Show directories and subdirectories in easilly readable file tree |
mc | Terminal file explorer (alternative to ncdu) |
touch <filename> | Creates or updates (edit) your file |
mktemp -t <filename> | Make a temp file in /tmp/ which is deleted at next boot (-d to make directory) |
cat <filename> | Displays file raw content (will not be interpreted) |
cat -n <filename> | Shows number of lines |
nl <file.sh> | Shows number of lines in file |
cat filename1 > filename2 | Copy filename1 to filename2 |
cat filename1 >> filename2 | Merge two files texts together |
any_command > <filename> | '>' is used to perform redirections, it will set any_command's stdout to file instead of "real stdout" (generally /dev/stdout) |
more <filename> | Shows the first part of a file (move with space and type q to quit) |
head <filename> | Outputs the first lines of file (default: 10 lines) |
tail <filename> | Outputs the last lines of file (useful with -f option) (default: 10 lines) |
vim <filename> | Opens a file in VIM (VI iMproved) text editor, will create it if it doesn't exist |
mv <filename1> <dest> | Moves a file to destination, behavior will change based on 'dest' type (dir: file is placed into dir; file: file will replace dest (tip: useful for renaming)) |
cp <filename1> <dest> | Copies a file |
rm <filename> | Removes a file |
find . -name <name> <type> | Searches for a file or a directory in the current directory and all its sub-directories by its name |
diff <filename1> <filename2> | Compares files, and shows where they differ |
wc <filename> | Tells you how many lines, words and characters there are in a file. Use -lwc (lines, word, character) to ouput only 1 of those informations |
sort <filename> | Sorts the contents of a text file line by line in alphabetical order, use -n for numeric sort and -r for reversing order. |
sort -t -k <filename> | Sorts the contents on specific sort key field starting from 1, using the field separator t. |
rev | Reverse string characters (hello becomes olleh) |
chmod -options <filename> | Lets you change the read, write, and execute permissions on your files (more infos: SUID, GUID) |
gzip <filename> | Compresses files using gzip algorithm |
gunzip <filename> | Uncompresses files compressed by gzip |
gzcat <filename> | Lets you look at gzipped file without actually having to gunzip it |
lpr <filename> | Prints the file |
lpq | Checks out the printer queue |
lprm <jobnumber> | Removes something from the printer queue |
genscript | Converts plain text files into postscript for printing and gives you some options for formatting |
dvips <filename> | Prints .dvi files (i.e. files produced by LaTeX) |
grep <pattern> <filenames> | Looks for the string in the files |
grep -r <pattern> <dir> | Search recursively for pattern in directory |
head -n file_name | tail +n | Print nth line from file. |
head -y lines.txt | tail +x | Want to display all the lines from x to y. This includes the xth and yth lines. |
sed 's/<pattern>/<replacement>/g' <filename> | Replace pattern in file with replacement value to std output the character after s (/) is the delimeter |
sed -i 's/<pattern>/<replacement>/g' <filename> | Replace pattern in file with replacement value in place |
echo "this" | sed 's/is/at/g' | Replace pattern from input stream with replacement value |
BASH DIRECTORY COMMANDS
Command | Explanation |
---|---|
mkdir <dirname> | makes a new directory |
rmdir <dirname> | remove an empty directory |
rmdir -rf <dirname> | remove a non-empty directory |
mv <dir1> <dir2> | rename a directory from <dir1> to <dir2> |
cd | **changes to home |
cd .. | changes to the parent directory |
cd <dirname> | **changes directory |
cp -r <dir1> <dir2> | copy <dir1> into <dir2> including sub-directories |
pwd | tells you where you currently are |
cd ~ | **changes to home. |
cd - | changes to previous working directory |
BASH SSH, SYSTEM INFO & NETWORK COMMANDS
Command | Explanation |
---|---|
ssh user@host | Connects to host as user |
ssh -p <port> user@host | Connects to host on specified port as user |
ssh-copy-id user@host | Adds your ssh key to host for user to enable a keyed or passwordless login |
whoami | Returns your username |
su <user> | Switch to a different user |
su - | Switch to root, likely needs to be sudo su - |
sudo <command> | Execute command as the root user |
passwd | Lets you change your password |
quota -v | Shows what your disk quota is |
date | Shows the current date and time |
cal | Shows the month's calendar |
uptime | Shows current uptime |
w | Displays whois online |
finger <user> | Displays information about user |
uname -a | Shows kernel information |
man <command> | Shows the manual for specified command |
info <command> | Shows another documentation system for the specific command |
help | Shows documentation about built-in commands and functions |
df | Shows disk usage |
du <filename> | Shows the disk usage of the files and directories in filename (du -s give only a total) |
resize2fs | ext2/ext3/ext4 file system resizer |
last <yourUsername> | Lists your last logins |
ps -u yourusername | Lists your processes |
kill <PID> | Kills the processes with the ID you gave |
killall <processname> | Kill all processes with the name |
top | Displays your currently active processes |
lsof | Lists open files |
bg | Lists stopped or background jobs ; resume a stopped job in the background |
fg | Brings the most recent job in the foreground |
fg <job> | Prings job to the foreground |
ping <host> | Pings host and outputs results |
whois <domain> | Gets whois information for domain |
dig <domain> | Gets DNS information for domain |
dig -x <host> | Reverses lookup host |
wget <file> | Downloads file |
netstat | Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships |
time <command> | Report time consumed by command execution |
BASH VARIABLES
Command | Explanation |
---|---|
varname=value | defines a variable |
varname=value command | defines a variable to be in the environment of a particular subprocess |
echo $varname | checks a variable's value |
echo $$ | prints process ID of the current shell |
echo $! | prints process ID of the most recently invoked background job |
echo $? | displays the exit status of the last command |
read <varname> | reads a string from the input and assigns it to a variable |
read -p "prompt" <varname> | same as above but outputs a prompt to ask user for value |
column -t <filename> | display info in pretty columns (often used with pipe) |
let <varname> = <equation> | *performs mathematical calculation using operators like +, -, , /, % |
export VARNAME=value | defines an environment variable (will be available in subprocesses) |
export -f <funcname> | Exports function 'funcname' |
export var1="var1 value" | Export and assign in the same statement |
export <varname> | **Copy Bash variable ** |
declare -x <varname> | **Copy Bash variable ** |
array[0]=valA, array[1]=valB, array[2]=valC | how to define an array |
array=([2]=valC [0]=valA [1]=valB) | another way |
array=(valA valB valC) | and another |
${array[i]} | displays array's value for this index. If no index is supplied, array element 0 is assumed |
${#array[i] } | to find out the length of any element in the array |
${#array[@]} | to find out how many values there are in the array |
declare -a | the variables are treated as arrays |
declare -f | uses function names only |
declare -F | displays function names without definitions |
declare -i | the variables are treated as integers |
declare -r | makes the variables read-only |
declare -x | marks the variables for export via the environment |
declare -l | uppercase values in the variable are converted to lowercase |
declare -A | makes it an associative array |
${varname:-word} | if varname exists and isn't null, return its value; otherwise return word |
${varname:word} | if varname exists and isn't null, return its value; otherwise return word |
${varname:=word} | if varname exists and isn't null, return its value; otherwise set it word and then return its value |
${varname:?message} | if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script |
${varname:+word} | if varname exists and isn't null, return word; otherwise return null |
${varname:offset:length} | performs substring expansion. It returns the substring of $varname starting at offset and up to length characters |
${variable#pattern} | if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest |
${variable##pattern} | if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest |
${variable%pattern} | if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest |
${variable%%pattern} | if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest |
${variable/pattern/string} | the longest match to pattern in variable is replaced by string. Only the first match is replaced |
${variable//pattern/string } | the longest match to pattern in variable is replaced by string. All matches are replaced |
${#varname} | returns the length of the value of the variable as a character string |
*(patternlist) | matches zero or more occurrences of the given patterns |
+(patternlist) | matches one or more occurrences of the given patterns |
?(patternlist) | matches zero or one occurrence of the given patterns |
@(patternlist) | matches exactly one of the given patterns |
!(patternlist) | matches anything except one of the given patterns |
$(UNIX command) | command substitution: runs the command and returns standard output |
typeset -l <x> | makes variable local - <x> must be an interger |
BASH FUNCTIONS
The function refers to passed arguments by position (as if they were positional parameters), that is, 2, and so forth.
$@
is equal to "$1" "$2"... "$N"
, where N
is the number of positional parameters. $#
holds the number of positional parameters.
function functname() {
shell commands
}
unset -f functname # deletes a function definition
declare -f # displays all defined functions in your login session
BASH FLOW CONTROLS
Command | Explanation |
---|---|
statement1 && statement2 | and operator |
statement1 || statement2 | or operator |
-a | and operator inside a test conditional expression |
-o | or operator inside a test conditional expression |
BASH STRINGS
Command | Explanation |
---|---|
str1 == str2 | str1 matches str2 |
str1 != str2 | str1 does not match str2 |
str1 < str2 | str1 is less than str2 (alphabetically) |
str1 > str2 | str1 is greater than str2 (alphabetically) |
str1 \> str2 | str1 is sorted after str2 |
str1 \< str2 | str1 is sorted before str2 |
-n str1 | str1 is not null (has length greater than 0) |
-z str1 | str1 is null (has length 0) |
BASH FILES
Command | Explanation |
---|---|
-a file | file exists or its compilation is successful |
-d file | file exists and is a directory |
-e file | file exists; same -a |
-f file | file exists and is a regular file (i.e., not a directory or other special type of file) |
-r file | you have read permission |
-s file | file exists and is not empty |
-w file | your have write permission |
-x file | you have execute permission on file, or directory search permission if it is a directory |
-N file | file was modified since it was last read |
-O file | you own file |
-G file | file's group ID matches yours (or one of yours, if you are in multiple groups) |
file1 -nt file2 | file1 is newer than file2 |
file1 -ot file2 | file1 is older than file2 |
BASH NUMBERS
Command | Explanation |
---|---|
-lt | less than |
-le | less than or equal |
-eq | equal |
-ge | greater than or equal |
-gt | greater than |
-ne | not equal |
if condition
then
statements
[elif condition
then statements...]
[else
statements]
fi
for x in {1..10}
do
statements
done
for name [in list]
do
statements that can use $name
done
for (( initialisation ; ending condition ; update ))
do
statements...
done
case expression in
pattern1 )
statements ;;
pattern2 )
statements ;;
esac
select name [in list]
do
statements that can use $name
done
while condition; do
statements
done
until condition; do
statements
done
BASH COMMAND-LINE PROCESSING CYCLE
The default order for command lookup is functions, followed by built-ins, with scripts and executables last. There are three built-ins that you can use to override this order: command
, builtin
and enable
.
Command | Explanation |
---|---|
command | removes alias and function lookup. Only built-ins and commands found in the search path are executed |
builtin | looks up only built-in commands, ignoring functions and commands found in PATH |
enable | enables and disables shell built-ins |
eval | takes arguments and run them through the command-line processing steps all over again |
BASH INPUT/OUTPUT REDIRECTORS
Command | Explanation |
---|---|
cmd1 | cmd2 | pipe; takes standard output of cmd1 as standard input to cmd2 |
< file | takes standard input from file |
> file | directs standard output to file |
>> file | directs standard output to file; append to file if it already exists |
> | file | forces standard output to file even if noclobber is set |
n> | file | forces output to file from file descriptor n even if noclobber is set |
<> file | uses file as both standard input and standard output |
n<>file | uses file as both input and output for file descriptor n |
n>file | directs file descriptor n to file |
n<file | takes file descriptor n from file |
n>>file | directs file description n to file; append to file if it already exists |
n>& | duplicates standard output to file descriptor n |
n<& | duplicates standard input from file descriptor n |
n>&m | file descriptor n is made to be a copy of the output file descriptor |
n<&m | file descriptor n is made to be a copy of the input file descriptor |
&>file | directs standard output and standard error to file |
<&- | closes the standard input |
>&- | closes the standard output |
n>&- | closes the ouput from file descriptor n |
n<&- | closes the input from file descriptor n |
| tee <file> | output command to both terminal and a file (-a to append to file) |
BASH PROCESS HANDLING
To suspend a job, type CTRL+Z
while it is running. You can also suspend a job with CTRL+Y
. This is slightly different from CTRL+Z
in that the process is only stopped when it attempts to read input from terminal. Of course, to interrupt a job, type CTRL+C
.
Command | Explanation |
---|---|
myCommand & | runs job in the background and prompts back the shell |
jobs | lists all jobs (use with -l to see associated PID) |
fg | brings a background job into the foreground |
fg %+ | brings most recently invoked background job |
fg %- | brings second most recently invoked background job |
fg %N | brings job number N |
fg %string | brings job whose command begins with string |
fg %?string | brings job whose command contains string |
kill -l | returns a list of all signals on the system, by name and number |
kill PID | terminates process with specified PID |
kill -s SIGKILL 4500 | sends a signal to force or terminate the process |
kill -15 913 | Ending PID 913 process with signal 15 (TERM) |
kill %1 | Where %1 is the number of job as read from 'jobs' command. |
ps | prints a line of information about the current running login shell and any processes running under it |
ps -a | selects all processes with a tty except session leaders |
trap cmd sig1 sig2 | executes a command when a signal is received by the script |
trap "" sig1 sig2 | ignores that signals |
trap - sig1 sig2 | resets the action taken when the signal is received to the default |
disown <PID | JID> | removes the process from the list of jobs |
wait | waits until all background jobs have finished |
sleep <number> | wait # of seconds before continuing |
pv | **display progress bar for data handling commands. often used with pipe like | pv ** |
yes | give yes response everytime an input is requested from script/process |
BASH TIPS & TRICKS
Set an alias
cd; nano .bash_profile
alias gentlenode='ssh admin@gentlenode.com -p 3404' # add your alias in .bash_profile
To quickly go to a specific directory
cd; nano .bashrc
> shopt -s cdable_vars
> export websites="/Users/mac/Documents/websites"
source .bashrc
cd $websites
DEBUGGING SHELL PROGRAMS IN BASH
Command | Explanation |
---|---|
bash -n scriptname | don't run commands; check for syntax errors only |
set -o noexec | alternative (set option in script) |
bash -v scriptname | echo commands before running them |
set -o verbose | alternative (set option in script) |
bash -x scriptname | echo commands after command-line processing |
set -o xtrace | alternative (set option in script) |
trap 'echo $varname' EXIT
- useful when you want to print out the values of variables at the point that your script exits|function errtrap { es=$? echo "ERROR line $1: Command exited with status $es." }
trap 'errtrap $LINENO' ERR
- is run whenever a command in the surrounding script or function exits with non-zero statusfunction dbgtrap { echo "badvar is $badvar" }
trap dbgtrap DEBUG
- causes the trap code to be executed before every statement in a function or script ...section of code in which the problem occurs...trap - DEBUG
- turn off the DEBUG trapfunction returntrap { echo "A return occurred" }
trap returntrap RETURN
- is executed each time a shell function or a script executed with the . or source commands finishes executing
BASH TEXT COLORS AND BACKGROUNDS
note:
\e
or\x1B
also work instead of\033
Color_Off='\033[0m'
- Text ResetRegular Colors
Black='\033[0;30m' # Black Red='\033[0;31m' # Red Green='\033[0;32m' # Green Yellow='\033[0;33m' # Yellow Blue='\033[0;34m' # Blue Purple='\033[0;35m' # Purple Cyan='\033[0;36m' # Cyan White='\033[0;97m' # White
Additional colors
LGrey='\033[0;37m' # Ligth Gray DGrey='\033[0;90m' # Dark Gray LRed='\033[0;91m' # Ligth Red LGreen='\033[0;92m' # Ligth Green LYellow='\033[0;93m'# Ligth Yellow LBlue='\033[0;94m' # Ligth Blue LPurple='\033[0;95m'# Light Purple LCyan='\033[0;96m' # Ligth Cyan
Bold
BBlack='\033[1;30m' # Black BRed='\033[1;31m' # Red BGreen='\033[1;32m' # Green BYellow='\033[1;33m'# Yellow BBlue='\033[1;34m' # Blue BPurple='\033[1;35m'# Purple BCyan='\033[1;36m' # Cyan BWhite='\033[1;37m' # White
Underline
UBlack='\033[4;30m' # Black URed='\033[4;31m' # Red UGreen='\033[4;32m' # Green UYellow='\033[4;33m'# Yellow UBlue='\033[4;34m' # Blue UPurple='\033[4;35m'# Purple UCyan='\033[4;36m' # Cyan UWhite='\033[4;37m' # White
Background
On_Black='\033[40m' # Black On_Red='\033[41m' # Red On_Green='\033[42m' # Green On_Yellow='\033[43m'# Yellow On_Blue='\033[44m' # Blue On_Purple='\033[45m'# Purple On_Cyan='\033[46m' # Cyan On_White='\033[47m' # White
Example of usage
echo -e "${Green}This is GREEN text${Color_Off} and normal text" echo -e "${Red}${On_White}This is Red test on White background${Color_Off}"
printf "${Red} This is red \n"
option -e is mandatory, it enable interpretation of backslash escapes
Related Bash Tutorials
- Dynamic variable names in Bash
- How to parse command line arguments in Bash?
- Bash and shell script variable capitalization?
- How to get the directory where a Bash script is located from within the script itself?
- Parsing JSON with Unix tools
- Command not found error in Bash variable assignment
- How to set a variable to the output of a command in Bash?
- How to run Bash commands in Python?
- Extract filename and extension in Bash? 10.Looping through the content of a file in Bash