Bash Cheat Sheet

< Blog

A quick reference to bash

Created on: 2019-02-03

Tag: cheat_sheet, living_in_the_shell

Warning

under heavy construction and not well organized

sed

find an replace

to find and replace:

sed -e 's/</\n&/g' << '<hello><world>'

Output:

<hello>
<world>

general pattern:

sed -e 's/$FIND/$REPALCE_WITH&/g' << '$STRING'

source: https://stackoverflow.com/a/8349811/

split a string with a delimiter

to split a string with a delimiter:

sed 's/delimiter/\n/g'

Like if we want to split the string "he:llo:you" with : delimiter, we do:

sed 's/:/\n/g' <<< "he:llo:you"

source: https://stackoverflow.com/a/18234407/

delete text before a delimiter

to delete text before a delimiter:

sed -i 's/^[^:]*:/:/' file

the delimiter is inside the [] and after ^ which is a :.

source: https://unix.stackexchange.com/a/149764/

delete string after delimiter

echo 'hello:world:again' |sed 's/:.*//'

source: https://stackoverflow.com/a/24555789

append a string at end of a specific line

to append a string at end of a specific line:

sed '2s/$/ myalias/' file

replace 2 with the line number.

source: https://stackoverflow.com/a/22159086/

deleting a substring

echo $str | sed -E 's/(.*?)\..*/\1/'

(source: http://stackoverflow.com/a/13570430/)

replace char with another char

sed -ie 's/char/achar/g' /path/to/hello.txt #replacing char with achar

(source: http://unix.stackexchange.com/a/159369/)

Replace whole line containing a string using sed

sed -i '/replace this/c\with this' /tmp/foo

append line before pattern in file

sed -i '/find this pattern/i \append pattern' /path/to/file.extension

delete specific line in file (creates a .bak file of same name)

sudo sed -i.bak -e '{line_number}d' /path/to/file.extension

delete from line to end of file

sed -i '1458,$d' filename.txt

source: https://unix.stackexchange.com/a/294129

delete the first 5 chars on any line with sed

sed 's/^.....//'

(source: https://stackoverflow.com/a/3806107/)

delete lines containing a specific string

sed -i '/pattern to match/d' ./infile

(source: https://stackoverflow.com/a/5410784/)

read specific line

to read/get/print specific line:

sed '$line_number!d' file_name

(source: http://stackoverflow.com/a/19327690/)

comment or uncomment ie. append before line using sed

sed -i 'start_line,end_line s/char_to_be_replaced/replacing_char/' file_name
#use ^ as char_to_be_replaced for unknown char_to_be_replaced

awk

find and replace

to find and replace:

echo '<hello><world>' | awk '{gsub(/</,"\n<",$0)}1'

general pattern:

echo $STRING'' | awk '{gsub(/$FIND/,"$REPALCE_WITH<",$0)}1'

source: https://stackoverflow.com/a/8349811/5350059

read specific line

to read/get/print specific line:

awk 'NR==$LINE' file

source: https://stackoverflow.com/a/19327690/

split string to array using awk

echo "12|23|11" | awk '{split($0,a,"|"); print a[3],a[2],a[1]}'

(source: http://stackoverflow.com/a/8009724/)

deleting a substring

::: echo $str | awk -F. '{print $1}'

(source: http://stackoverflow.com/a/13570430/)

Get a spcecifice column form output

command | awk '{print $n}' #n is the number of column

Get a spcecifice row column output

command | awk 'FNR == row {print $column}' #row is row/line number and column is column number

Skip first line

cat file | awk 'FNR > 1 { print $2 }'

OR

awk 'FNR > 1 { print $2 }' file

source: https://unix.stackexchange.com/a/198066/

Merge 2 columns separated by colon

cat file | awk 'FNR>1 {print $1 ":" $2}'

source: https://stackoverflow.com/a/34775751/

others

save command output in variable

OUTPUT="$(ls -1)"
echo "${OUTPUT}"

echo in red color

echo -e "\e[31m{message to echo with out 2nd brackets}\e[0m"

(source: http://stackoverflow.com/a/28938235/)

Get current directory name (without full path)

dir="$(pwd | grep -o '[^/]*$')"

OR:

result=${PWD##*/}

source: https://stackoverflow.com/a/1371283/

Press Enter to continue

read -p "Press Enter to continue"

take one line from file and save it in a variable

var1="$(head -n 1 file | tail -n 1)" #save line 1 on in var1
var2="$(head -n 2 file | tail -n 1)" #save line 2 on in var2

read on same line after echoing a message

read -p "[y/n]: " opt (#saves value in opt variable)

(source: http://stackoverflow.com/a/9720209/)

split a string on a delimiter

string="1;2"
echo $string | cut -d';' -f1 # output is 1
echo $string | cut -d';' -f2 # output is 2

(source: http://stackoverflow.com/a/38905821/)

clear screen

printf "\033c"

(source: http://stackoverflow.com/a/5367075/)

deleting a substring

str=abc.out

#shell:
echo ${str%.\*}


#grep:
echo $str | grep -o '^[^\.]*'

#sed:
echo $str | sed -E 's/(.*?)\..*/\1/'

#awk:
echo $str | awk -F. '{print $1}'

#cut:
echo $str | cut -d. -f1

#All output:
abc

(source: http://stackoverflow.com/a/13570430/)

split a sting with OIFS

IN="bla@some.com;john@home.com"
OIFS=$IFS
IFS=';'
mails2=$IN
for x in $mails2
do
    echo "> [$x]"
done
IFS=$OIFS

(source: http://stackoverflow.com/q/918886/)

if string is not empty

if [ ! -z "$string" ]
#OR
if [[ ! -z $string ]]

(source: http://stackoverflow.com/a/6592241/)

if else if elif

   if [ expression 1 ]
   then
      Statement(s) to be executed if expression 1 is true
   elif [ expression 2 ]
   then
      Statement(s) to be executed if expression 2 is true
   else
      Statement(s) to be executed if no expression is true
   fi

(source: https://www.tutorialspoint.com/unix/if-elif-statement.htm)

multiple conditions in if

to put multiple conditions in if:

if [ "$option" = "Y" ] || [ "$option" = "y" ]
then
    echo "Entered $option"
fi

here || is used as example, replace with with && if need be.

source: https://stackoverflow.com/a/28064741/

if string is equal to string

string="ABC"
if [ "$string" = "XYZ" ]; then
    echo "string matched"
else
    echo "string mismatched"
fi;

(source: http://stackoverflow.com/a/10849346/)

if a application exist

e=$(which $app_name)
if [[ ! -z "$e" ]]
then
    echo -e "\e[32mApplication exist.\e[0m"
else
    echo -e "\e[31mApplication doens't exist!!!\e[0m"
fi

insert line number in file

cat -n inputfile > result
#OR
nl infile
#OR
nl -w1 -s.\  infile
#OR
cat <inputfile> | grep -n '' > <outputfile>

(source: http://www.unix.com/shell-programming-and-scripting/99016-how-add-line-numbers-text-file.html)

get number of line in a file

wc -l file.txt | awk '{print $1}'
#OR
wc -l < file.txt

add, sub, multiply and devide

swap_size="$(($ram * $size_choice))"

(source: https://stackoverflow.com/a/11039905

OR:

expr $x / $y

(source: http://stackoverflow.com/a/18093887/)

use specific app through ssh

ssh -X username@xxx.xxx.xxx.xxx
nohup $app_name &

(source: http://tiny.cc/i04fjy)

detect line break

if [[ "$a" == '\012' ]] ; then
            echo "FOUND NEWLINE"
    fi

(source: http://unix.stackexchange.com/q/27423/)

kill a shell form that shell

kill $$

get file name from file path

file_path=/path/to/file.extension
file=$(basename "$file_path")
echo "$file"

(source: http://stackoverflow.com/a/4645575/)

kill all instance of an application

e="$(ps ax | grep $app | awk '{print $1}')"
kill $e

convert to lowercase

var= "HI ALL"
low=$(echo "$var" | tr '[:upper:]' '[:lower:]')
low=$(echo "$var" | awk '{print tolower($0)}')
#both produces "hi all"

(source: http://stackoverflow.com/a/2264537/)

get real ip

curl -s checkip.dyndns.org | sed -e 's/.*Current IP Address: //' -e 's/<.*$//'

(source: http://sh.howtocode.com.bd/3.4.3.secure-connection.html)

delete script after execution

#add at the end of script
rm -- "$0"
#OR
rm $script_name

(source: http://stackoverflow.com/a/8981233/)

unzip .zip

unzip file.zip -d destination_folder

(source: http://askubuntu.com/a/86852/)

go to each sub directory and execute a command

for d in ./*/
do
    (cd "$d" && somecommand)
done

(source: http://unix.stackexchange.com/a/171679/)

change password without typing (non interactive)

echo $uname:$passwd | sudo chpasswd

(source: http://stackoverflow.com/a/41223440/)

refresh output in the same line(echo update)

echo -e "\e[1A" # moving the cursor back to the previously printed line
echo -ne "$line\e[K" # \e[K cleans the residues of the previous output.
#example:
#!/bin/bash
arr=(12 11 10 9 8 7 6 5 4 3 2 1 0)
for i in ${arr[@]}
do
    echo -e "\e[1A"
    sleep 1s;
    echo -ne "Waiting time : "$i" Seconds\e[K"
done
echo #print new line

(source: http://stackoverflow.com/a/34466100/)

go back to last visited directory

cd -

(source: https://superuser.com/q/113219/)

rm move to trash

#in .bashrc
#start by defining a move_to_trash function:
move_to_trash () {
    mv "$@" /path/to/trash #/home/$USER/.local/share/Trash/files
}
#then alias rm to that:
alias rm='move_to_trash'

(source: https://unix.stackexchange.com/a/42758/)

use pc name instead of ip while ssh

#add at the end of /etc/hosts
ip_address(tab)pc_name

(source: https://askubuntu.com/a/487319/)

shutdown, restart, without sudo from terminal [munst have consolekit]

A safe way to do this without using sudo and without tinkering with the system, is by executing these one-liner commands: For Ubuntu 14.10 or earlier: Shutdown:

/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.ConsoleKit" /org/freedesktop/ConsoleKit/Manager org.freedesktop.ConsoleKit.Manager.Stop

Restart:

/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.ConsoleKit" /org/freedesktop/ConsoleKit/Manager org.freedesktop.ConsoleKit.Manager.Restart

Suspend:

/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Suspend

Hibernate(if enabled on your system):

/usr/bin/dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Hibernate

For Ubuntu 15.04 and later[This is due to Ubuntu's shift in using systemd instead of Upstart]:

systemctl poweroff

systemctl reboot

systemctl suspend

systemctl hibernate

systemctl hybrid-sleep

(source: http://askubuntu.com/a/385316/)

gnome-session-quit --power-off --force --no-prompt

https://askubuntu.com/a/714940

run applications as root

#console
sudo <program name>
#GUI
gksudo <program name>

(source: http://askubuntu.com/a/207467/)

grep for this or that (2 things) in a file?

grep -E '(then|there)' x.x

(source: https://unix.stackexchange.com/a/82993/)

execute date inside corntab

0 * * * * echo hello >> ~/cron-logs/hourly/test_`date "+\%d-\%b-\%Y"`

(source: https://unix.stackexchange.com/a/29582/)

execute sudo command over ssh

ssh -t user@server "sudo script"

(source: https://stackoverflow.com/a/10312700/)

see port address and PID

netstat -tulpn

check curl and install if not found

::: if command -v curl > /dev/null then echo "Detected curl..." else echo "Installing curl..." apt-get install -q -y curl fi

special dollar sign shell variables

$1, $2, $3, ... are the positional parameters.
"$@" is an array-like construct of all positional parameters, {$1, $2, $3 ...}.
"$*" is the IFS expansion of all positional parameters, $1 $2 $3 ....
$# is the number of positional parameters.
$- current options set for the shell.
$$ pid of the current shell (not subshell).
$_ most recent parameter (or the abs path of the command to start the current shell immediately after startup).
$IFS is the (input) field separator.
$? is the most recent foreground pipeline exit status.
$! is the PID of the most recent background command.
$0 is the name of the shell or shell script.

(source: https://stackoverflow.com/a/5163260)

show files only

ls -p | grep -v /

(source: https://askubuntu.com/questions/811210/how-can-i-make-ls-only-display-files#811236)

disallow peter from logging in

sudo usermod --expiredate 1 peter

set expiration date of peter to Never

sudo usermod --expiredate "" peter

take away peters password

sudo passwd -l peter

give peter back his password

sudo passwd -u peter

make peter think of a new password on login

sudo passwd -e  YYYY-MM-DD peter

(source: https://askubuntu.com/a/607108/)

set static ip

#edit /etc/network/interfaces and put the following there, don't forget to change $interface and address, netmask, network, gateway and dns
auto $interface
iface $interface inet static
   address 10.253.0.50
   netmask 255.255.255.0
   network 10.253.0.0
   gateway 10.253.0.1
   dns-nameservers 8.8.8.8

(source: https://askubuntu.com/a/470245/)

Login with sshpass

sshpass -p 'your_password' ssh user@host_ip

Show line number in nano for 'filename'

#Show while opening file
nano -c [filename]
#Show always
nano ~/.nanorc
#don't worry if its empty - this file doesn't exist by default
set const
#save

Record your encryption passphrase in Ubuntu

ecryptfs-unwrap-passphrase

See USB information in Linux Terminal

user@user-pc:~$ lsusb
// open terminal and type lsusb
user@user-pc:~$ Bus #bus_number Device #device_number: ID #vendor:#product USB_Name
//output of command 'lsusb' including your expected device
user@user-pc:~$ lsusb -D /dev/bus/usb/#bus_number/#device_number
//replace the #bus_number and #device_number of you expected device

Shell script to install application(s) in Ubuntu

method 01

#!/bin/sh
apt-get update  # To get the latest package lists
apt-get install <package name> -y #apt-get install <package name> -y
#etc.

method 02

#!/bin/sh
LIST_OF_APPS="a b c d e"
aptitude update
aptitude install -y $LIST_OF_APPS

method 03

cat example.list | xargs sudo apt-get -y install

method 04

#!/bin/bash
apt-get update  # To get the latest package lists
apt-get install $1 -y

Connect to wifi from terminal

List all the wifi:

nmcli dev wifi

connect to wifi:

nmcli dev wifi connect $SSID password $PASS

What are some funny Linux commands

make:

make LOVE=war

rev: reverse char of a line in a file:

rev <file> # if file contains 12 shows 21

fortune will display some random sentence #sudo apt-get install fortune:

fortune

yes command will keep displaying the string for infinite until the process is killed by the user.:

yes yes

figlet command can be installed with apt-get, comes with some ascii fonts which are located in /usr/share/figlet. cd /usr/share/figlet figlet -f Ex: figlet -f big.flf unixmen

asciiquarium command will transform your terminal in to a Sea Aquarium:

search Term-Animation in http://www.cpan.org/authors/id/K/KB/KBAUCOM/

bb:

apt-get install bb
bb

(source: https://www.quora.com/What-are-some-funny-Linux-commands)

show notification in linux

#must have libnotify for notify-send
#install libnotify
sudo apt-get install libnotify-bin
#install notify-send
sudo apt-get install notify-osd
DISPLAY=:0.0 /usr/bin/notify-send "title" "Message"

notification at a specific time

echo 'notify-send "Work day is done!"' | at 4:00PM
echo 'notify-send "Get your tea!"' | at now + 3 minutes
echo 'notify-send "Meeting in 1 hour with the big boss!"' | at 1pm tomorrow

Mute the microphone

amixer set Capture nocap

Unmute the microphone

amixer set Capture cap

chnage avatar (must be png)

sudo cp /path/to/file /var/lib/AccountsService/icons/$(whoami)

stopwatch and countdown timer function

countdown(){
    date1=$((`date +%s` + $1));
    while [ "$date1" -ge `date +%s` ]; do
    ## Is this more than 24h away?
    days=$(($(($(( $date1 - $(date +%s))) * 1 ))/86400))
    echo -ne "$days day(s) and $(date -u --date @$(($date1 - `date +%s`)) +%H:%M:%S)\r";
    sleep 0.1
    done
}
stopwatch(){
    date1=`date +%s`;
    while true; do
    days=$(( $(($(date +%s) - date1)) / 86400 ))
    echo -ne "$days day(s) and $(date -u --date @$((`date +%s` - $date1)) +%H:%M:%S)\r";
    sleep 0.1
    done
}

(source: http://superuser.com/a/611582)

using rsync to mirror

rsync -ar source/ destination

hide (all) user list on login screen

sudo mkdir -p /etc/lightdm/lightdm.conf.d
sudo printf "[SeatDefaults]\nuser-session=ubuntu\ngreeter-show-manual-login=true\ngreeter-hide-users=true\nall" > /etc/lightdm/lightdm.conf.d/10-ubuntu.conf

(source: http://askubuntu.com/a/731455/)

hide a specific user form login screen

touch $user_name
printf "[User]\nSystemAccount=true\n" > $user_name
sudo mv $user_name /var/lib/AccountsService/users/$user_name

(source: http://askubuntu.com/a/575390/)

open files form terminal

#Ubuntu
nautilus .

see execution time of a command

time command
#for getting real time only
/usr/bin/time -f "%e" command
#save the command execution time in a variable
down_time=`/usr/bin/time -f %e sleep 2 2>&1`

run a terminal-lunched program after closing terminal (by removing it form job list)

app_name & disown

delete last char of string

#with bash 4.2
a=123
echo "${a::-1}"
12

#older bash
a=123
echo "${a: : -1}"
12

open chrome using crontab (as because cron can do terminal jobs only we need to export DISPLAY for GUI)

export DISPLAY=:0
/opt/google/chrome/chrome $URL

stop max brightness on restart

sudo -v
#get directory name
cd /sys/class/backlight/*/ && dir="$(pwd | grep -o '[^/]*$')"
#the following line added the given pattern twice as there is a exit 0 in the comment section, delete it mannualy
#250 is the number of brightness level
sudo sed -i "/exit 0/i \echo 250 > /sys/class/backlight/$dir/brightness" /etc/rc.local

(source: http://askubuntu.com/a/151665/)

Execute a command in the background using '&' and killing it

./my-shell-script.sh & #execute command in background

jobs #see jobs
[1]+  Running        my-shell-script.sh #sample output

kill %1 #kill with the number in [n]+ recived from jobs

jobs #see jobs
[1]+  Terminated    ./my-shell-script.sh #sample output

terminal based lan chat

pc1: nc -l $port
pc2: nc $IP $port

open a terminal and execute shell on that terminal using crontab

export DISPLAY=:0 && /usr/bin/gnome-termina -e /path/to/script

display network traffic in terminal

tcpdump -i $interface #(i.e. eth0,wlan0)
#OR
netstat -tnp
#OR
sudo watch -n1 netstat -tunap

assign ip to interface

::: sudo ip ad add $ip/$subnet dev $interface i.e. sudo ip ad add 10.0.0.10/24 dev eth0

connect two pc over crossover cable

#on pc 1
sudo ip ad add 10.0.0.10/24 dev eth0
#on pc 2
sudo ip ad add 10.0.0.20/24 dev eth0

recursively list all files in a directory

ls -LR
#OR
find -follow

(source: http://stackoverflow.com/a/105249/)

check battery status

upower -i $(upower -e | grep 'BAT') | grep -E "state|to\ full|percentage"
#OR
cat /proc/acpi/battery/BAT0/info
#OR
cat /proc/acpi/battery/BAT0/state

schedule jobs with cron

corntab -e #run jobs for user
sudo corntab -e #run jobs for root user

show jobs schedule with cron

corntab -l #show jobs for user
sudo corntab -e #show jobs for root user

change bluetooth broadcast device name

sudo echo "PRETTY_HOSTNAME=$device_name" >>/etc/machine-info
sudo service bluetooth restart
#OR (source: http://askubuntu.com/a/80964/)
sudo hciconfig hci0 name '$device_name'

(source: http://askubuntu.com/a/80963/)

change LCD brightness

display="$(xrandr -q | grep " connected" | awk '{print $1}')"
xrandr --output $display --brightness m.n #(0<=m<=10(tested can be greater),0<=m<=9 )

(source: http://askubuntu.com/a/149264/)

export display (to run a GUI of a program in remote client like over ssh)

export DISPLAY=:0 && program command

read file from line x to the end of a file (read from specific line)

linesToSkip=1

{ for ((i=$linesToSkip;i--;)) ;do read done while read line ;do echo
$line done } < file.csv

(source: http://stackoverflow.com/a/14110529/)

copy all except one file or folder

shopt -s extglob && cp source\!($name) \destination #(first part extends regexes)

(idea source: http://askubuntu.com/a/786613/ & http://stackoverflow.com/a/27655311/)

get date in yyy-mm-dd format

DATE=`date +%Y-%m-%d`

(source: http://stackoverflow.com/a/1401495/)

in ubuntu all .deb file are in this folder

/var/cache/apt/archives

install all .deb

sudo dpkg -i *.deb #(* for all)

Encrypting and compressing with 7z

7z a -p stuff.7z MyStuff
   ^  ^    ^        ^
   |  |    |        `--- Files/directories to compress & encrypt.
   |  |    `--- Output filename
   |  `---- Use a password
   `---- Add files to archive

(source: http://unix.stackexchange.com/a/325783/)

bluetooth tool

hcitool

Terminal Hacks

#see wather in terminal
curl http://wttr.in/$name_of_city

#Increase the maximum volume of your speakers by a certain percentage (150 in this case)
pactl set-sink-volume 0 150%

#Scroll Lock toggle
xmodmap -e 'add mod3 = Scroll_Lock' link

#opens any file directly from terminal in the default application
Xdg-open file/link

#run a command you ran yesterday at a point of time
ctrl+r #(mod command using ctrl+a, ctrl+e, ctrl+left, ctrl+right)

#list files only in current folder/path
ls -p | grep -v /

#list directory only in current folder/path
ls -d */

#run your last used command
!!

#Delete word by word from the terminal
alt+backspace

#see all input device
xinput list
#disable input device (see form "xinput list" command output id column)
xinput set-prop $id "Device Enabled" 0
#enable input device (see form "xinput list" command output id column)
xinput set-prop $id "Device Enabled" 1
#if mouse found in usb dieable touchpad see github Code.random

(source: https://www.quora.com/What-are-the-best-Linux-Terminal-hacks-that-you-can-learn-in-10-seconds)

reboot alsamixer

sudo alsa force-reload

download YouTube video with youtube-dl

youtube-dl  --sub-lang en --sub-format srt --batch-file youtube_url.txt

add bookmark in nautilus

echo "location_path $name_of_bookmark" >> ~/.gtk-bookmarks

(source: https://ubuntuforums.org/showthread.php?t=1736534)

speaker test

speaker-test -t sine -f 1000 -l 1

(source: http://unix.stackexchange.com/a/163716)

disable and enable mouse driver

sudo modprobe -r psmouse  # disable the driver
sudo modprobe psmouse # enable the mouse driver

(source: https://askubuntu.com/a/697952/)

list all users and groups

getent passwd #user
getent group #group

(source: https://serverfault.com/a/355294)

turn off bluetooth on startup ubuntu

#the following line added the given pattern twice as there is a exit 0 in the comment section, delete it mannualy
sudo sed -i '/exit 0/i \rfkill block bluetooth' /etc/rc.local

(source: https://itsfoss.com/turn-off-bluetooth-by-default-in-ubuntu-14-04/)

check if user is sudo if not ask for password

sudo -v

(source: https://superuser.com/a/553939/)

echo in system file

echo "line to be added" | sudo tee -a /etc/fstab

(source: https://ubuntuforums.org/showthread.php?t=978334)

missing date & time from top panel

dconf reset -f /com/canonical/indicator/datetime/
pkill -f datetime

(source: https://askubuntu.com/a/462176/)

spell checking in vim

#while editing on vim
:set spell spelllang=en_us
#
echo "set spell spelllang=en_us" >> ~/.vimrc #chnage en_us to any language you want

(source: https://www.linux.com/learn/using-spell-checking-vim)

compare two file and get the diff

comm -2 -3 <(sort file1) <(sort file2) > file3 #here we will redrict the output to file3

(source: https://stackoverflow.com/a/4546712)

remove a fixed prefix/suffix from a strin or delete string from string

string="hello-world"
prefix="hell"
suffix="ld"
foo=${string#$prefix}
foo=${foo%$suffix}
echo "${foo}" #o-wor

(source: https://stackoverflow.com/a/16623897)

if file exists

if [ -e x.txt ]
then
    echo "ok"
else
    echo "not ok"
fi

(source: https://stackoverflow.com/a/40082454)

read file line by line

filename="$1"
while read -r line
do
        echo $line
done < "$filename"

(source: https://stackoverflow.com/a/10929955)

if a sub string is part of string

string='My long string'
if [[ $string == *"My long"* ]]; then
    echo "It's there!"
fi

(source: https://stackoverflow.com/a/229606)

generate a random filename in unix shell

# generates a srting consisting of alpha(a-z) and num(0-9) of 32 char
cat /dev/urandom | tr -cd 'a-f0-9' | head -c 32

(source: https://stackoverflow.com/a/2793856)

crontab log

grep CRON /var/log/syslog

(source: https://askubuntu.com/a/56811)

using git commands in shell script

#!/bin/sh
GIT=`which git`
REPO_DIR=/home/username/Sites/git/repo/
cd ${REPO_DIR}
${GIT} add --all .
${GIT} commit -m "Test commit"
${GIT} push git@bitbucket.org:username/repo.git master

(source: https://unix.stackexchange.com/a/226678)

numbers of line in a commands output

ps aux | grep "docker" | wc -l

backup and restore crontab

#backup
crontab -l > crontab_backup
#restore
crontab crontab_backup

(source: http://www.roman10.net/2012/07/09/how-to-backup-crontab-settings/)

execute command without keeping it in history

command;history -d $(history 1)

(source: https://stackoverflow.com/a/33511637/)

just add a space before your command

get hostname from ip

nbtscan <ip> #install nbtscan sudo apt-get install nbtscan

(source: https://askubuntu.com/a/205067/)

connect to net using ethernet calbe if you have DHCP enabled

   sudo dhclient eth0

(source: https://askubuntu.com/a/755263/)

change hostname in linux

   sudo hostname your-new-name #name shows after reboot

(source: https://askubuntu.com/a/87687/)

change the default shell

sometime after doing ssh to a machine we see just `$` or `#` instead of the very familer user@hostname$ thats beacuse the default shell for that user is not set or not bash.:

sudo chsh <username> -s /bin/bash

(source: https://unix.stackexchange.com/q/50264/)

if your .bashrc is lost

#normal user
/bin/cp /etc/skel/.bashrc ~/
#root
cp /etc/bash.bashrc ~/.bashrc

(source: https://askubuntu.com/a/404428/ and me)

show last octet of ip

vim .bashrc
ip=lo:$(ifconfig | grep "inet " | grep -v 127.0.0. | awk '{print $2}' | cut -d . -f 4)
ip=$(echo "$ip" | tr '\n' '/')
ip="${ip::-1}"
PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h($ip)\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

make video with image and audio

ffmpeg -loop 1 -i image.jpg -i audio.AMR -c:v libx264 -tune stillimage -c:a aac -b:a 192k -pix_fmt yuv420p -shortest video.mp4

(source: https://superuser.com/a/1041818/)

show ubuntu-support-status

ubuntu-support-status

get all system info as html page

sudo lshw -html>sys.html

open a GUI app from terminal while keeping the terminal clean form log output

$app 2>/dev/null & disown

nmap find all alive hostnames and IPs in LAN

nmap -sP first_3_octet.*

(source: https://serverfault.com/a/153779)

get current IP if first interface is being used

ifconfig | grep "inet " | awk 'FNR == 1 {print $2}' | cut -d: -f2 #if first interface is not being used change the FNR == number of interface

get first 3 octet of network if first interface is being used

ifconfig | grep "inet " | awk 'FNR == 1 {print $2}' | cut -d: -f2 | cut -d. -f1,2,3 #if first interface is not being used change the FNR == number of interface

convert a .pdf into .jpg [one-page-one-pic]

pdftoppm -jpeg raw-er-cowboyra.pdf prefix

(source: https://askubuntu.com/a/50180/)

suppress all output from a command

scriptname >/dev/null

(source: https://stackoverflow.com/a/617184/)

make a dir with - in fornt of it

touch -- -$folder_name

(source: udemy.com/intro-to-bash-linux-command-line section:6 lecture:23)

standard streams

stdin 0
stdout 1
stderr 2

(source: https://en.wikipedia.org/wiki/Standard_streams)

see gup info

sudo lshw -C display

print contents of X events

all mouse, keyboard event event can be used to test other input device:

xev

(source: https://linux.die.net/man/1/xev)

mute and unmute a microphone

#mute
amixer set Capture nocap
#unmute
amixer set Capture cap

(source: https://askubuntu.com/a/337662/)

enabling and disabling Ethernet

#enable
sudo ip link set up eth0
#disable
sudo ip link set down eth0

(source: https://askubuntu.com/a/739502/)

add a timestamp to script log?

(date && script.sh) >> /var/log/logfile

(source: https://serverfault.com/a/310648)

run PHP from terminal

php filename.php

(source: https://askubuntu.com/a/447254/)

wget show progress bar only

wget $url -q --show-progress

(source: https://stackoverflow.com/a/29457649/)

redirect output to multiple log files

echo test | tee file1 file2 file3

(source: https://unix.stackexchange.com/a/41249/)

single line sftp from terminal

   sftp username@hostname:remoteFileName localFileName

(source: https://stackoverflow.com/a/16723151/)

check if file exists on remote host with ssh

if ssh $HOST stat $FILE_PATH \> /dev/null 2\>\&1
then
    echo "File exists"
else
    echo "File does not exist"
fi

(source: https://stackoverflow.com/a/12845254/)

cleanest way to ssh and run multiple commands source

ssh otherhost << EOF
  ls some_folder;
  ./someaction.sh 'some params'
  pwd
  ./some_other_action 'other params'
EOF

(source: https://stackoverflow.com/a/4412338/)

passing variables in remote ssh command

ssh pvt@192.168.1.133 "~/tools/run_pvt.pl $BUILD_NUMBER"

(source: https://stackoverflow.com/a/3314678/)

whether or not a variable is empty

if [[ -z "$var" ]]

(source: https://stackoverflow.com/a/3063887/)

debug a bash script

set -x
..code to debug...
set +x

(source: https://unix.stackexchange.com/a/155570/)

print a char variable times

printf '%0.s-' $(seq 1 $var)

https://stackoverflow.com/a/17030976

lock and unlock screen over ssh

#this is for gnome
ssh -X user@server "export DISPLAY=:0; gnome-screensaver-command -l"

(source: https://z-computer-z.blogspot.com/2010/01/remote-lock-screen-and-remote-unlock.html)

getting WiFi network details in Raspberry Pi

sudo iwlist wlan0 scan #(source: https://www.raspberrypi.org/documentation/configuration/wireless/wireless-cli.md)

#OR

iwgetid # (source: https://raspberrypi.stackexchange.com/a/41024)

download and output it on STDOUT

wget -qO- $link

(source: https://stackoverflow.com/a/22926472/)

image your hard disk using dd

(source: http://www.linuxweblog.com/dd-image)

use curl to download tar file

to use curl to download tar file:

curl -L https://site.tld/file.tar.b2 | tar zx

source: https://stackoverflow.com/a/5746376/

file sync

#!/bin/sh
exitcode=1
#do check if usb flash is mounted
if test -e '/your_path_to_usb_mountpoint';then
exitcode=0
#from folder to usb if the files are newers
rsync -avun --inplace  /your_folder_wich_you_want_to_syncronize/ /your_path_to_usb_mountpoint ;
#from usb to folder if the files are newers
rsync -avun --inplace /your_path_to_usb_mountpoint/ /your_folder_wich_you_want_to_syncronize/
fi
#if the flash is not mounted exit with exitcode=1
exit $exitcode

number of arguments equal

to check if number of arguments is equal to a number:

if [[ "$#" -ne 1 ]]; then
    echo "Illegal number of parameters"
fi

s: https://stackoverflow.com/a/18568726/

set environment variables

::: export MY_VAR=value

https://linuxize.com/post/how-to-set-and-list-environment-variables-in-linux/

global variable declaration

declare -g variable

https://stackoverflow.com/a/58594644/

remove alias

to remove alias:

unalias $ALIAS

https://askubuntu.com/a/325380/

export variable from bash script

we can export variable from bash script. If our shell is test.sh and it contains:

#! /usr/bin/env bash
export VAR="HELLO, VARIABLE"
echo "hello"

To run we will use:

. ./test.sh

Instead of ./test.sh, this will source the file and run it at the same time. The output:

hello

The environment variable is also set which gives the output on echo:

echo $VAR

HELLO, VARIABLE

source: Can I export a variable to the environment from a bash script without sourcing it?

remove an exported variable

to remove an exported variable:

unset $VAIABLE

source: How do I delete an exported environment variable?

create a django secret key with bash

to create a django secret key with bash:

export SECRET_KEY=$(head /dev/urandom | tr -dc 'A-Za-z0-9!"#$%&'\''()*+,-./:;<=>?@[\]^_`{|}~' | head -c 49 ; echo '')

source: How to generate a random string?

write multiple line to a file with variables

to write multiple line to a file with variables:

VAR=4
cat > $FILE_NAME.EXT << EOL
line 1
line 2
line 3
line ${VAR}
EOL

P.S: We can replace the EOL with anything like CAT ;)

source: How to write multiple line string using Bash with variables?

remove user from a group

to remove a user from a group:

sudo gpasswd -d $USER $GROUP

source: How do I remove a user from a group?

keyboard shortcut for recalling last argument

to recall last argument use the following keyboard shortcut:

Alt + .

source: https://stackoverflow.com/a/3371299/ and https://askubuntu.com/a/304831/

run nc -q with millisecond

to run nc -q with millisecond:

nc 192.168.1.106 23 -q 10ms

Warning

need to check if it works

source: https://stackoverflow.com/a/42137257/

array in bash

create an empty array

to create an empty array:

ARR=()

save data to aa array

to save data to an array:

ARR[0]="A"
ARR[1]="B"
ARR[2]="C"

OR:

ARR=("A" "B" "C")

length of an array

to check the length of an array:

${#ARR[@]}

access an element of an array

to access an element of an array:

echo ${ARR[0]}

all elements in an array

get all elements in an array:

${ARR[*]}

source: https://stackoverflow.com/a/52331532/

add element to array

to add element to array:

ARRAY=()
ARRAY+=('foo')
ARRAY+=('bar')

source: https://stackoverflow.com/a/1951523/

sort array

to sort an array:

IFS=$'\n' sorted=($(sort <<<"${array[*]}"))
unset IFS

source: https://stackoverflow.com/a/11789688/

append elements to array inside for loop

to append elements to array inside for loop:

declare -ag exceeded_users
arr=()
for i in {1..5}
do
    arr+=($i)
done

the declare -ag exceeded_users part is the most important.

source: https://stackoverflow.com/a/58594644/

get from char to char of a string

to cut a specific length of a string like, 3rd char to 6th char:

str="abcdefghij"
char=${str:2:4}

so it is like ${parameter:offset:length}

source: https://stackoverflow.com/a/7306483/

remove symbolic link

to remove symbolic link:

rm linked_file

source: https://askubuntu.com/a/398850/

convert character to ASCII

to convert character to ASCII:

printf "%d\n" "'A"

OR:

echo "A" | tr -d "\n" | od -An -t dC

convert ASCII to character:

awk -v char=65 'BEGIN { printf "%c\n", char; exit }'

source: https://www.unix.com/shell-programming-and-scripting/93355-how-get-ascii-value-using-shell-commands-script.html

delete large directory with thousands of files

to delete large directory with thousands of files:

mkdir empty_dir
rsync -a --delete empty_dir/    yourdirectory/

OR:

cd yourdirectory
perl -e 'for(<*>){((stat)[9]<(unlink))}'

source: https://unix.stackexchange.com/a/79656/

curl output HTTP status

see curl output HTTP status:

curl -s -o /dev/null -I -w "%{http_code}" http://www.example.org/

source: https://superuser.com/a/442395/

output specific line of huge file

to output specific line of huge file:

sed -n -e $LINEp file_name

source: https://stackoverflow.com/a/8166496/

OR:

head -$LINE file_name | tail -1

output line range of huge file

to output line range of huge file:

sed -n $START_LINE,$END_LINEp file_name

source: https://stackoverflow.com/a/8166496/

sort by specific field

to sort by 4th field:

sort -k4

source: https://stackoverflow.com/a/5243126/

show file contains with file name

to show file contains with file name:

tail -n +1 file1.txt file2.txt file3.txt

Output:

==> file1.txt <==
<contents of file1.txt>

==> file2.txt <==
<contents of file2.txt>

==> file3.txt <==
<contents of file3.txt>

source: https://stackoverflow.com/a/7816490/

get current path of a symlink

to get the current path of a symlink:

DIR="$(cd "$(dirname "$0")" && pwd)"

source: https://unix.stackexchange.com/a/17500/

less show line number

to show line number in less:

less -N file_name

source: https://stackoverflow.com/a/831707/

grep certain file extensions

to grep certain file extensions:

grep -r -i -include=\*.${file_extension} /path/to/dir

source: https://stackoverflow.com/a/12517022/

detecting change in files in a directory

to detect change in files in a directory we can use inotifywait:

inotifywait -r  -m /dir/to/monitor/

source: https://unix.stackexchange.com/a/283875/

or with find command:

while :
do
    find /dir/to/monitor/ -type f -mmin $TIME_IN_SECOND
done

strange echo and redirection

I just noticed some thing strange with echo and redirection:

echo "" >> file.txt newline

This command I would assume would give me a file named file.txt with nothing in it but instead it gives:

user@:host~$ cat file.txt
 newline
user@:host~$

It's the text after file name with a space before it. If we do:

echo >> file.txt newline

We see:

user@:host~$ cat file.txt
newline
user@:host~$

Now as we see the space before the text is gone.

tar extract to a directory

Use the -C flag:

tar -xf archive.tar -C /target/directory

source: https://askubuntu.com/a/45354

cut with new line

cat file.cut | cut -d$'\n' -f1

source: https://stackoverflow.com/a/21757210

list all apt key

sudo apt-key list

source: https://askubuntu.com/a/107189

check if a remote port is open

nc -z <host> <port>

add a 5 seconds wait with:

nc -z -v -w5 <host> <port>

source: https://stackoverflow.com/a/9463554

find file created or modified between a time range

find -newermt "2017-11-06 17:30:00" ! -newermt "2017-11-06 22:00:00" -ls

source: https://stackoverflow.com/a/23508622

find a file with name and delete

find / -name $FILE_NAME -print0 | xargs -0 rm

source: https://unix.stackexchange.com/a/167824

for loop with delimiter

variable=abc,def,ghij
for i in ${variable//,/ }
do
        # call your procedure/other scripts here below
        echo "$i"
done

source: https://stackoverflow.com/a/35894538

for loop skip to next

for i in something
do
        [ condition ] && continue
        cmd1
        cmd2
done

source: https://www.cyberciti.biz/faq/unix-linux-bsd-appleosx-continue-in-bash-loop/

break from loop

done=0
while : ; do
  ...
  if [ "$done" -ne 0 ]; then
          break
  fi
done

source: https://stackoverflow.com/a/18488730

conditional match regex string

if [[ $gg == ????grid* ]] ; then echo $gg; fi

source: https://stackoverflow.com/a/2348495

delete first n character

var="pid: 1234"
var=${var:5}

source: https://stackoverflow.com/a/11470727

check if directory is git repository without entering it

to check if a directory is git repository without entering it:

git -C /path/to/repo rev-parse

If it returns 0 then it is a git repo.

source: https://stackoverflow.com/a/39518382

pass command line arguments to a shell alias

Normal alias can't take command line arguments but if the alias is a function that it can take the command line arguments and process it:

alias blah='function _blah(){ echo "First: $1"; echo "Second: $2"; };_blah'

source: https://stackoverflow.com/a/22684652

xclip read from a file

read from file to xclip:

xclip -sel clip < ~/path/to/file.txt

source: https://unix.stackexchange.com/a/204555

https://stackoverflow.com/a/59839

find string in all files in directory

to find string in all files in directory:

grep -R "$STRING" *

source: https://superuser.com/a/345103

cat reverse

to do reverse cat:

tac $FILE_NAME

source: https://stackoverflow.com/a/742485

sort files by modified date

to sort files by modified date:

ls -t

to do the sort in reverse:

ls -tr

source: https://superuser.com/a/147030

version backup file with timestamp

to do version backup file with timestamp:

rsync -ab --backup-dir=versions --suffix="."$(date +"%Y%m%d%H%M") --delete /source/folder/ /destination/folder

source: https://askubuntu.com/a/1108698

rsync mirror directory

to mirror directory with rsync:

rsync -avh source/ dest/ --delete

source: https://askubuntu.com/a/665918