Bash-oneliner: A collection of handy Bash one-liners and terminal tricks

Bash-oneliner: A collection of handy Bash one-liners and terminal tricks

This is the unbelievable item ever!

I am glad that you are here! I was working on bioinformatics a few years ago and was amazed by those single-word bash commands which are much faster than my dull scripts, time saved through learning command-line shortcuts and scripting. Recent years I am working on cloud computing and I keep recording those useful commands here. Not all of them is oneliner, but i put effort on making them brief and swift. I am mainly using Ubuntu, Amazon Linux, RedHat, Linux Mint, Mac and CentOS, sorry if the commands don’t work on your system.

This blog will focus on simple bash commands for parsing data and Linux system maintenance that i acquired from work and LPIC exam. I apologize that there are no detailed citation for all the commands, but they are probably from dear Google and Stackoverflow.

English and bash are not my first language, please correct me anytime, thank you.
If you know other cool commands, please teach me!

Here’s a more stylish version of Bash-Oneliner~

Handy Bash one-liners

Terminal Tricks
Condition and Loop
Data Wrangling

Terminal Tricks
Using Ctrl keys
Ctrl + n : same as Down arrow.
Ctrl + p : same as Up arrow.
Ctrl + r : begins a backward search through command history.(keep pressing Ctrl + r to move backward)
Ctrl + s : to stop output to terminal.
Ctrl + q : to resume output to terminal after Ctrl + s.
Ctrl + a : move to the beginning of line.
Ctrl + e : move to the end of line.
Ctrl + d : if you’ve type something, Ctrl + d deletes the character under the cursor, else, it escapes the current shell.
Ctrl + k : delete all text from the cursor to the end of line.
Ctrl + x + backspace : delete all text from the beginning of line to the cursor.
Ctrl + t : transpose the character before the cursor with the one under the cursor, press Esc + t to transposes the two words before the cursor.
Ctrl + w : cut the word before the cursor; then Ctrl + y paste it
Ctrl + u : cut the line before the cursor; then Ctrl + y paste it
Ctrl + _ : undo typing.
Ctrl + l : equivalent to clear.
Ctrl + x + Ctrl + e : launch editor defined by $EDITOR to input your command. Useful for multi-line commands.

Change case
Esc + u
# converts text from cursor to the end of the word to uppercase.
Esc + l
# converts text from cursor to the end of the word to lowercase.
Esc + c
# converts letter under the cursor to uppercase, rest of the word to lowercase.
Run history number (e.g. 53)

Run last command
# run the previous command using sudo
sudo !!
# of course you need to enter your password
Run last command and change some parameter using caret substitution (e.g. last command: echo ‘aaa’ -> rerun as: echo ‘bbb’)
#last command: echo ‘aaa’

#echo ‘bbb’

#Notice that only the first aaa will be replaced, if you want to replace all ‘aaa’, use ‘:&’ to repeat it:

Run past command that began with (e.g. cat filename)
# or
# run cat filename again
Bash globbing
# ‘*’ serves as a “wild card” for filename expansion.
/etc/pa*wd #/etc/passwd

# ‘?’ serves as a single-character “wild card” for filename expansion.
/b?n/?at #/bin/cat

# ‘[]’ serves to match the character from a range.
ls -l [a-z]* #list all files with alphabet in its filename.

# ‘{}’ can be used to match filenames with more than one patterns
ls {*.sh,*.py} #list all .sh and .py files
Some handy environment variables
$0 :name of shell or shell script.
$1, $2, $3, … :positional parameters.
$# :number of positional parameters.
$? :most recent foreground pipeline exit status.
$- :current options set for the shell.
$$ :pid of the current shell (not subshell).
$! :is the PID of the most recent background command.

$DESKTOP_SESSION current display manager
$EDITOR preferred text editor.
$LANG current language.
$PATH list of directories to search for executable files (i.e. ready-to-run programs)
$PWD current directory
$SHELL current shell
$USER current username
$HOSTNAME current hostname

[back to top]

Variable substitution within quotes
# foo=bar
echo “‘$foo'”
# double/single quotes around single quotes make the inner single quotes expand variables
Get the length of variable
var=”some string”
echo ${#var}
# 11
Get the first character of the variable
echo “${var:0:1}”

# or
echo ${var%%”${var#?}”}
Remove the first or last string from variable
var=”some string”
echo ${var:2}
#me string
Replacement (e.g. remove the first leading 0 )
echo ${var[@]#0}
Replacement (e.g. replace ‘a’ with ‘,’)

Replace all (e.g. replace all ‘a’ with ‘,’)

#with grep
test=”god the father”
grep ${test// /\|} file.txt
# turning the space into ‘or’ (|) in grep
To change the case of the string stored in the variable to lowercase (Parameter Expansion)
echo ${var,,}
Expand and then execute variable/argument
eval “$cmd”
echo “$bar” # foo
[back to top]

Arithmetic Expansion in Bash (Operators: +, -, *, /, %, etc)
echo $(( 10 + 5 )) #15
echo $(( x++ )) #1 , notice that it is still 1, since it’s post-incremen
echo $(( x++ )) #2
echo $(( ++x )) #4 , notice that it is not 3 since it’s pre-incremen
echo $(( x– )) #4
echo $(( x– )) #3
echo $(( –x )) #1
echo $(( x ** y )) #8
Print out the prime factors of a number (e.g. 50)

Sum up input list (e.g. seq 10)

Sum up a file (each line in file contains only one number)
awk ‘{s+=$1} END {print s}’ filename
Column subtraction
cat file| awk -F ‘t’ ‘BEGIN {SUM=0}{SUM+=$3-$2}END{print SUM}’
Simple math with expr
expr 10+20 #30
expr 10*20 #600
expr 30 > 20 #1 (true)
More math with bc
# Number of decimal digit/ significant figure
echo “scale=2;2/3” | bc

# Exponent operator
echo “10^2” | bc

# Using variables
echo “var=5;–var”| bc
[back to top]

Type of grep
grep=grep -G # Basic Regular Expression (BRE)
fgrep=grep -F # fixed text, ignoring meta-charachetrs
egrep=grep -E # Extended Regular Expression (ERE)
pgrep=grep -P # Perl Compatible Regular Expressions (PCRE)
rgrep=grep -r # recursive
Grep and count number of empty lines

Grep and return only integer
grep -o ‘[0-9]*’
grep -oP ‘d’
Grep integer with certain number of digits (e.g. 3)
grep ‘[0-9]{3}’
# or
grep -E ‘[0-9]{3}’
# or
grep -P ‘d{3}’
Grep only IP address
grep -Eo ‘[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}’
# or
grep -Po ‘d{1,3}.d{1,3}.d{1,3}.d{1,3}’
Grep whole word (e.g. ‘target’)
grep -w ‘target’

#or using RE
grep ‘btargetb’
Grep returning lines before and after match (e.g. ‘bbo’)
# return also 3 lines after match
grep -A 3 ‘bbo’

# return also 3 lines before match
grep -B 3 ‘bbo’

# return also 3 lines before and after match
grep -C 3 ‘bbo’
Grep string starting with (e.g. ‘S’)

Extract text between words (e.g. w1,w2)
grep -o -P ‘(? all.json”>sed -s ‘$a,’ *.json> all.json
Substitution (e.g. replace A by B)

Substitution with wildcard (e.g. replace a line start with aaa=by aaa=/my/new/path)
sed “s/aaa=.*/aaa=/my/new/path/g”
Select lines start with string (e.g. ‘bbo’)

Delete lines with string (e.g. ‘bbo’)

Print/get/trim a range of line (e.g. line 500-5000)
sed -n 500,5000p filename
Print every nth lines
sed -n ‘0~3p’ filename

# catch 0: start; 3: step
Print every odd # lines

Print every third line including the first line

Remove leading whitespace and tabs
sed -e ‘s/^[ t]*//’
# Notice a whitespace before ‘t’!!
Remove only leading whitespace
sed ‘s/ *//’

# notice a whitespace before ‘*’!!
Remove ending commas

Add a column to the end
sed “s/$/t$i/”
# $i is the valuable you want to add

# To add the filename to every last column of the file
for i in $(ls);do sed -i “s/$/t$i/” $i;done
Add extension of filename to last column
for i in T000086_1.02.n T000086_1.02.p;do sed “s/$/t${i/*./}/” $i;done>
Remove newline nextline

Print a particular line (e.g. 123th line)

Print a number of lines (e.g. line 10th to line 33 rd)
sed -n ‘10,33p’ AAA#AAA)
sed -r -e ‘s/^.{3}//’ file
[back to top]

Set tab as field separator

Output as tab separated (also as field separator)

Pass variable
awk -v a=”$a” -v b=”$b” “$1==a && $10=b” filename
Print line number and number of characters on each line
awk ‘{print NR,length($0);}’ filename
Find number of columns

Reverse column order

Check if there is a comma in a column (e.g. column $1)

Split and do for loop
awk ‘{split($2, a,”,”);for (i in a) print $1″t”a[i]}’ filename
Print all lines before nth occurrence of a string (e.g stop print lines when ‘bbo’ appears 7 times)
awk -v N=7 ‘{print}/bbo/&& –Nfile’ file.txt”>ls |sed ‘s/.txt//g’|xargs -n1 -I file sed -i -e ‘1 i>file’ file.txt
Count all files

Turn output into a single line

Count files within directories
echo mso{1..8}|xargs -n1 bash -c ‘echo -n “$1:”; ls -la “$1″| grep -w 74 |wc -l’ —
# “–” signals the end of options and display further option processing
Count lines in all file, also count total lines

Xargs and grep
cat grep_list |xargs -I{} grep {} filename
Xargs and sed (replace all old ip address with new ip address under /etc directory)
grep -rl ‘’ /etc | xargs sed -i ‘s/’
[back to top]

List all sub directory/file in the current directory

List all files under the current directory

List all directories under the current directory

Edit all files under current directory (e.g. replace ‘www’ with ‘ww’)
find . -name ‘*.php’ -exec sed -i ‘s/www/w/g’ {} ;

# if there are no subdirectory
replace “www” “w” — *
# a space before *
Find and output only filename (e.g. “mso”)
find mso*/ -name M* -printf “%fn”
Find large files in the system (e.g.>4G)

Find and delete file with size less than (e.g. 74 byte)
find . -name “*.mso” -size -74c -delete

# M for MB, etc
Find empty (0 byte) files
find . -type f -empty
# to further delete all the empty files
find . -type f -empty -delete
Recursively count all the files in a directory

Condition and loop
[back to top]

If statement
# if and else loop for string matching
if [[ “$c”==”read” ]]; then outputdir=”seq”; else outputdir=”write” ; fi

# Test if myfile contains the string ‘test’:
if grep -q hello myfile; then echo -e “file contains the string!” ; fi

# Test if mydir is a directory, change to it and do other stuff:
if cd mydir; then
echo ‘some content’>myfile
echo>&2 “Fatal error. This script requires mydir.”

# if variable is null
if [ ! -s “myvariable” ]; then echo -e “variable is null!” ; fi
#True of the length if “STRING” is zero.

# Using test command (same as []), to test if the length of variable is nonzero
test -n “$myvariable” && echo myvariable is “$myvariable” || echo myvariable is not set

# Test if file exist
if [ -e ‘filename’ ]
echo -e “file exists!”

# Test if file exist but also including symbolic links:
if [ -e myfile ] || [ -L myfile ]
echo -e “file exists!”

# Test if the value of x is greater or equal than 5
if [ “$x” -ge 5 ]; then echo -e “greater or equal than 5!” ; fi

# Test if the value of x is greater or equal than 5, in bash/ksh/zsh:
if ((x>=5)); then echo -e “greater or equal than 5!” ; fi

# Use (( )) for arithmetic operation
if ((j==u+2)); then echo -e “j==u+2!!” ; fi

# Use [[ ]] for comparison
if [[ $age -gt 21 ]]; then echo -e “forever 21!!” ; fi

More if commands

For loop
# Echo the file name under the current directory
for i in $(ls); do echo file $i;done
for i in *; do echo file $i; done

# Make directories listed in a file (e.g. myfile)
for dir in $(at now + 1min #time-units can be minutes, hours, days, or weeks
warning: commands will be executed using /bin/sh
at> echo hihigithub>~/itworks
at> # press Ctrl + D to exit
job 1 at Wed Apr 18 11:16:00 2018
[back to top]

Download the content of this (the one your are viewing now)
curl | pandoc -f markdown -t man | man -l –

# or w3m (a text based web browser and pager)
curl | pandoc | w3m -T text/html

# or using emacs (in emac text editor)
emacs –eval ‘(org-mode)’ –insert # To bring your key with you when ssh to serverA, then ssh to serverB from serverA using the key.
ssh-add /path/to/mykey.pem
ssh -A @
# Next you can ssh to serverB
ssh @
Set the default user and key for a host when using SSH
# add the following to ~/.ssh/config
Host myserver
User myuser
IdentityFile ~/path/to/mykey.pem

# Next, you could run “ssh myserver” instead of “ssh -i ~/path/to/mykey.pem myuser@myserver”
Follow the most recent logs from service
journalctl -u -f
Eliminate the zombie
# A zombie is already dead, so you cannot kill it. You can eliminate the zombie by killing its parent.
# First, find PID of the zombie
ps aux| grep ‘Z’
# Next find the PID of zombie’s parent
pstree -p -s
# Then you can kill its parent and you will notice the zombie is gone.
sudo kill 9
Show memory usage
free -c 10 -mhs 1
# print 10 times, at 1 second interval
Display CPU and IO statistics for devices and partitions.
# refresh every second
iostat -x -t 1
Display bandwidth usage on an network interface (e.g. enp175s0f0)

Tell how long the system has been running and number of users

Check if it’s root running
if [ “$EUID” -ne 0 ]; then
echo “Please run this as root”
exit 1
Change shell of a user (e.g. bonnie)
chsh -s /bin/sh bonnie
# /etc/shells: valid login shells
Change root / fake root / jail (e.g. change root to newroot)
chroot /home/newroot /bin/bash

# To exit chroot
Display file status (size; access, modify and change time, etc) of a file (e.g. filename.txt)

Snapshot of the current processes

Display a tree of processes

Find maximum number of processes
cat /proc/sys/kernel/pid_max
Print or control the kernel ring buffer

Show IP address
$ip add show

# or
Print previous and current SysV runlevel

Change SysV runlevel (e.g. 5)

Display all available services in all runlevels,
chkconfig –list
# update-rc.d equivalent to chkconfig in ubuntu
Check system version

Linux Programmer’s Manuel: hier- description of the filesystem hierarchy

Control the systemd system and service manager
# e.g. check the status of cron service
systemctl status cron.service

# e.g. stop cron service
systemctl stop cron.service
List job

Run a program with modified priority (e.g. ./
# nice value is adjustable from -20 (most favorable) to +19
# the nicer the application, the lower the priority
# Default niceness: 10; default priority: 80

nice -10 ./
Export PATH
export PATH=$PATH:~/path/you/want
Make file executable
chmod +x filename
# you can now ./filename to execute it
Print system information
uname -a

# Check system hardware-platform (x86-64)
uname -i
Surf the net

Add user, set passwd
useradd username
passwd username
Edit PS1 variable for bash (e.g. displaying the whole path)
1. vi ~/.bash_profile
2. export PS1=’u@h:w$’
# $PS1 is a variable that defines the makeup and style of the command prompt
# You could use emojis and add timestamp to every prompt using the following value:
# export PS1=”t@🦁:w$ ”
3. source ~/.bash_profile
Edit environment setting (e.g. alias)
1. vi ~/.bash_profile
2. alias pd=”pwd” //no more need to type that ‘w’!
3. source ~/.bash_profile
Print all alias

Unalias (e.g. after alias ls=’ls –color=auto’)

Set and unset shell options
# print all shell options

# to unset (or stop) alias
shopt -u expand_aliases

# to set (or start) alias
shopt -s expand_aliases
List environment variables (e.g. PATH)
echo $PATH
# list of directories separated by a colon
List all environment variables for current user

Unset environment variable (e.g. unset variable ‘MYVAR’)

Show partition format

Inform the OS of partition table changes

Soft link program to bin
ln -s /path/to/program /home/usr/bin
# must be the whole path to the program
Show hexadecimal view of data
hexdump -C filename.class
Jump to different node

Check port (active internet connection)

Print resolved symbolic links or canonical file names

Find out the type of command and where it link to (e.g. python)
type python
# python is /usr/bin/python
# There are 5 different types, check using the ‘type -f’ flag
# 1. alias (shell alias)
# 2. function (shell function, type will also print the function body)
# 3. builtin (shell builtin)
# 4. file (disk file)
# 5. keyword (shell reserved word)

# You can also use `which`
which python
# /usr/bin/python
List all functions names

List total size of a directory

Copy directory with permission setting
cp -rp /path/to/directory
Store current directory
pushd .

# then pop

#or use dirs to display the list of currently remembered directories.
dirs -l
Show disk usage
df -h

# or
du -h

du -sk /var/log/* |sort -rn |head -10
check the Inode utilization
df -i
# Filesystem Inodes IUsed IFree IUse% Mounted on
# devtmpfs 492652 304 492348 1% /dev
# tmpfs 497233 2 497231 1% /dev/shm
# tmpfs 497233 439 496794 1% /run
# tmpfs 497233 16 497217 1% /sys/fs/cgroup
# /dev/nvme0n1p1 5037976 370882 4667094 8% /
# tmpfs 497233 1 497232 1% /run/user/1000

Show all file system type

Show current runlevel

Switch runlevel

Permanently modify runlevel
1. edit /etc/init/rc-sysinit.conf
Become root

Become somebody

Report user quotes on device

Get entries in a number of important databases
getent database_name

# (e.g. the ‘passwd’ database)
getent passwd
# list all user account (all local and LDAP)

# (e.g. fetch list of grop accounts)
getent group
# store in database ‘group’
Change owner of file
chown user_name filename
chown -R user_name /path/to/directory/
# chown user:group filename
Mount and unmount
# e.g. Mount /dev/sdb to /home/test
mount /dev/sdb /home/test

# e.g. Unmount /home/test
umount /home/test
List current mount detail

List current usernames and user-numbers

Get all username
getent passwd| awk ‘{FS=”[:]”; print $1}’
Show all users

Show all groups

Show group of user

Show uid, gid, group of user
id username

# variable for UID
echo $UID
Check if it’s root
if [ $(id -u) -ne 0 ];then
echo “You are not root!”
# ‘id -u’ output 0 if it’s not root
Find out CPU information
more /proc/cpuinfo

# or
Set quota for user (e.g. disk soft limit: 120586240; hard limit: 125829120)
setquota username 120586240 125829120 0 0 /home
Show quota for user

Display current libraries from the cache

Print shared library dependencies (e.g. for ‘ls’)

Check user login

Check last reboot history

Edit path for all users
joe /etc/environment
# edit this file
Show and set user limit

Print out number of cores/ processors

Check status of each core

Show jobs and PID

List all running services

Schedule shutdown server
shutdown -r +5 “Server will restart in 5 minutes. Please save your work.”
Cancel scheduled shutdown

Broadcast to all users

Kill all process of a user

Kill all process of a program
kill -9 $(ps aux | grep ‘program_name’ | awk ‘{print $2}’)
Set gedit preference on server
# You might have to install the following:

apt-get install libglib2.0-bin;
# or
yum install dconf dconf-editor;
yum install dbus dbus-x11;

# Check list
gsettings list-recursively

# Change some settings
gsettings set org.gnome.gedit.preferences.editor highlight-current-line true
gsettings set org.gnome.gedit.preferences.editor scheme ‘cobalt’
gsettings set org.gnome.gedit.preferences.editor use-default-font false
gsettings set org.gnome.gedit.preferences.editor editor-font ‘Cantarell Regular 12’

Add user to a group (e.g add user ‘nice’ to the group ‘docker’, so that he can run docker without sudo)
sudo gpasswd -a nice docker
Pip install python package without root
1. pip install –user package_name
2. You might need to export ~/.local/bin/ to PATH: export PATH=$PATH:~/.local/bin/
Removing old linux kernels (when /boot almost full…)
1. uname -a #check current kernel, which should NOT be removed
2. sudo apt-get purge linux-image-X.X.X-X-generic #replace old version
Change hostname
sudo hostname your-new-name

# if not working, do also:
hostnamectl set-hostname your-new-hostname
# then check with:
# Or check /etc/hostname

# If still not working…, edit:
#add HOSTNAME=”your-new-hostname”
List installed packages
apt list –installed

# or on Red Hat:
yum list installed
Check for package update
apt list –upgradeable

# or
sudo yum check-update
Run yum update excluding a package (e.g. do not update php packages)
sudo yum update –exclude=php*
Check which file make the device busy on umount

When sound not working
killall pulseaudio
# then press Alt-F2 and type in pulseaudio
When sound not working

List information about SCSI devices

Tutorial for setting up your own DNS server

Tutorial for creating a simple daemon

Tutorial for using your gmail to send email

Using telnet to test open ports, test if you can connect to a port (e.g 53) of a server (e.g

Change network maximum transmission unit (mtu) (e.g. change to 9000)

Get pid of a running process (e.g python)
pidof python

# or
ps aux|grep python
Check status of a process using PID
ps -p

cat /proc//status
cat /proc//stack
cat /proc//stat
# Start ntp:

# Check ntp:
ntpq -p
Remove unnecessary files to clean your server
sudo apt-get autoremove
sudo apt-get clean
sudo rm -rf ~/.cache/thumbnails/*

# Remove old kernal:
sudo dpkg –list ‘linux-image*’
sudo apt-get remove linux-image-OLDER_VERSION
Increase/ resize root partition (root partition is an LVM logical volume)
lvextend -L +130G /dev/rhel/root -r
# Adding -r will grow filesystem after resizing the volume.
Create a UEFI Bootable USB drive (e.g. /dev/sdc1)
sudo dd if=~/path/to/isofile.iso of=/dev/sdc1 oflag=direct bs=1048576
Locate and remove a package
sudo dpkg -l | grep
sudo dpkg –purge
Create a ssh tunnel
ssh -f -L 9000:targetservername:8088 root@ -N
#-f: run in background; -L: Listen; -N: do nothing
#the 9000 of your computer is now connected to the 8088 port of the targetservername through
#so that you can see the content of targetservername:8088 by entering localhost:9000 from your browser.
Get process ID of a process (e.g. sublime_text)
pidof sublime_text

#pgrep, you don’t have to type the whole program name
pgrep sublim

#pgrep, echo 1 if process found, echo 0 if no such process
pgrep -q sublime_text && echo 1 || echo 0

#top, takes longer time
top|grep sublime_text
Some benchmarking tools for your server
aio-stress – AIO benchmark.

bandwidth – memory bandwidth benchmark.

bonnie++ – hard drive and file system performance benchmark.

dbench – generate I/O workloads to either a filesystem or to a networked CIFS or NFS server.

dnsperf – authorative and recursing DNS servers.

filebench – model based file system workload generator.

fio – I/O benchmark.

fs_mark – synchronous/async file creation benchmark.

httperf – measure web server performance.

interbench – linux interactivity benchmark.

ioblazer – multi-platform storage stack micro-benchmark.

iozone – filesystem benchmark.

iperf3 – measure TCP/UDP/SCTP performance.

kcbench – kernel compile benchmark, compiles a kernel and measures the time it takes.

lmbench – Suite of simple, portable benchmarks.

netperf – measure network performance, test unidirectional throughput, and end-to-end latency.

netpipe – network protocol independent performance evaluator.

nfsometer – NFS performance framework.

nuttcp – measure network performance.

phoronix-test-suite – comprehensive automated testing and benchmarking platform.

seeker – portable disk seek benchmark.

siege – http load tester and benchmark.

sockperf – network benchmarking utility over socket API.

spew – measures I/O performance and/or generates I/O load.

stress – workload generator for POSIX systems.

sysbench – scriptable database and system performance benchmark.

tiobench – threaded IO benchmark.

unixbench – the original BYTE UNIX benchmark suite, provide a basic indicator of the performance of a Unix-like system.

wrk – HTTP benchmark.

Performance monitoring tool – sar
# installation
# It collects the data every 10 minutes and generate its report daily. crontab file (/etc/cron.d/sysstat) is responsible for collecting and generating reports.
yum install sysstat
systemctl start sysstat
systemctl enable sysstat

# show CPU utilization 5 times every 2 seconds.
sar 2 5

# show memory utilization 5 times every 2 seconds.
sar -r 2 5

# show paging statistics 5 times every 2 seconds.
sar -B 2 5

# To generate all network statistic:
sar -n ALL

# reading SAR log file using -f
sar -f /var/log/sa/sa31|tail
Reading from journal file
journalctl –file ./log/journal/a90c18f62af546ccba02fa3734f00a04/system.journal –since “2020-02-11 00:00:00”
Show a listing of last logged in users.

Show a listing of current logged in users, print information of them

Show who is logged on and what they are doing

Print the user names of users currently logged in to the current host.

Stop tailing a file on program terminate
tail -f –pid=filename.txt
# replace with the process ID of the program.
List all enabled services
systemctl list-unit-files|grep enabled
[back to top]

Collect and summarize all hardware info of your machine
lshw -json>report.json
# Other options are: [ -html ] [ -short ] [ -xml ] [ -json ] [ -businfo ] [ -sanitize ] ,etc
Finding Out memory device detail

Print detail of CPU hardware
dmidecode -t 4
# Type Information
# 0 BIOS
# 1 System
# 2 Base Board
# 3 Chassis
# 4 Processor
# 5 Memory Controller
# 6 Memory Module
# 7 Cache
# 8 Port Connector
# 9 System Slots
# 11 OEM Strings
# 13 BIOS Language
# 15 System Event Log
# 16 Physical Memory Array
# 17 Memory Device
# 18 32-bit Memory Error
# 19 Memory Array Mapped Address
# 20 Memory Device Mapped Address
# 21 Built-in Pointing Device
# 22 Portable Battery
# 23 System Reset
# 24 Hardware Security
# 25 System Power Controls
# 26 Voltage Probe
# 27 Cooling Device
# 28 Temperature Probe
# 29 Electrical Current Probe
# 30 Out-of-band Remote Access
# 31 Boot Integrity Services
# 32 System Boot
# 34 Management Device
# 35 Management Device Component
# 36 Management Device Threshold Data
# 37 Memory Channel
# 38 IPMI Device
# 39 Power Supply
Count the number of Segate hard disks
lsscsi|grep SEAGATE|wc -l
# or
sg_map -i -x|grep SEAGATE|wc -l
Get UUID of a disk (e.g. sdb)
lsblk -f /dev/sdb

# or
sudo blkid /dev/sdb
Generate an UUID

Print detail of all hard disks
#where ROTA means rotational device / spinning hard disks (1 if true, 0 if false)
List all PCI (Peripheral Component Interconnect) devices
# List information about NIC
lspci | egrep -i –color ‘network|ethernet’
List all USB devices

Linux modules
# Show the status of modules in the Linux Kernel

# Add and remove modules from the Linux Kernel

# or
# Remove a module

# Insert a module
Controlling IPMI-enabled devices (e.g. BMC)
# Remotely finding out power status of the server
ipmitool -U -P -I lanplus -H power status

# Remotely switching on server
ipmitool -U -P -I lanplus -H power on

# Turn on panel identify light (default 15s)
ipmitool chassis identify 255

# Found out server sensor temperature
ipmitool sensors |grep -i Temp

# Reset BMC
ipmitool bmc reset cold

# Prnt BMC network
ipmitool lan print 1

# Setting BMC network
ipmitool -I bmc lan set 1 ipaddr
ipmitool -I bmc lan set 1 netmask
ipmitool -I bmc lan set 1 defgw ipaddr
[back to top]

Resolve a domain to IP address(es)
dig +short

# or
Get DNS TXT record a of domain
dig -t txt

# or
host -t txt
Send a ping with a limited TTL to 10 (TTL: Time-To-Live, which is the maximum number of hops that a packet can travel across the Internet before it gets discarded.)

Print the route packets trace to network host

Check connection to host (e.g. check connection to port 80 and 22 of
nc -vw5 80
# Connection to 80 port [tcp/http] succeeded!

nc -vw5 22
# nc: connect to port 22 (tcp) timed out: Operation now in progress
# nc: connect to port 22 (tcp) failed: Network is unreachable
Nc as a chat tool!
# From server A:
$ sudo nc -l 80
# then you can connect to the 80 port from another server (e.g. server B):
# e.g. telent 80
# then type something in server B
# and you will see the result in server A!
Check which ports are listening for TCP connections from the network
#notice that some companies might not like you using nmap
nmap -sT -O localhost

# check port 0-65535
nmap -p0-65535 localhost
Check if a host is up and scan for open ports, also skip host discovery.
#skips checking if the host is alive which may sometimes cause a false positive and stop the scan.
$ nmap -Pn

# Example output:
# Starting Nmap 7.01 ( ) at 2020-07-18 22:59 CST
# Nmap scan report for (
# Host is up (0.013s latency).
# Other addresses for (not scanned): 2404:6800:4008:802::200e
# rDNS record for
# Not shown: 998 filtered ports
# 80/tcp open http
# 443/tcp open https
# Nmap done: 1 IP address (1 host up) scanned in 3.99 seconds
Scan for open ports and OS and version detection (e.g. scan the domain “”)
$ nmap -A -T4
# -A to enable OS and version detection, script scanning, and traceroute; -T4 for faster execution
Look up website information (e.g. name server), searches for an object in a RFC 3912 database.

Show the SSL certificate of a domain
openssl s_client -showcerts -connect
Display IP address

Display route table

Display ARP cache (ARP cache displays the MAC addresses of device in the same network that you have connected to)

Add transient IP addres (reset after reboot) (e.g. add to device eno16777736)
ip address add dev eno16777736
Persisting network configuration changes
sudo vi /etc/sysconfig/network-scripts/ifcfg-enoxxx
# then edit the fields: BOOTPROT, DEVICE, IPADDR, NETMASK, GATEWAY, DNS1 etc
Refresh NetworkManager

Restart all interfaces
sudo systemctl restart network.service
To view hostname, OS, kernal, architecture at the same time!

Set hostname (set all transient, static, pretty hostname at once)
hostnamectl set-hostname “mynode”
Find out the web server (e.g Nginx or Apache) of a website
curl -I
# HTTP/1.1 200 OK
# Server: nginx
# Date: Thu, 02 Jan 2020 07:01:07 GMT
# Content-Type: text/html
# Content-Length: 1119
# Connection: keep-alive
# Vary: Accept-Encoding
# Last-Modified: Mon, 09 Sep 2019 10:37:49 GMT
# ETag: “xxxxxx”
# Accept-Ranges: bytes
# Vary: Accept-Encoding
Find out the http status code of a URL
curl -s -o /dev/null -w “%{http_code}”
Unshorten a shortended URL
curl -s -o /dev/null -w “%{redirect_url}”
Perform network throughput tests
# server side:
$ sudo iperf -s -p 80

# client side:
iperf -c –parallel 2 -i 1 -t 2 -p 80
To block port 80 (HTTP server) using iptables.
sudo iptables -A INPUT -p tcp –dport 80 -j DROP

# only block connection from an IP address
sudo iptables –A INPUT –s -p tcp –dport 80 –j DROP
Data wrangling
[back to top]

Print some words that start with a particular string (e.g. words start with ‘phy’)
# If file is not specified, the file /usr/share/dict/words is used.
look phy|head -n 10
# Phil
# Philadelphia
# Philadelphia’s
# Philby
# Philby’s
# Philip
# Philippe
# Philippe’s
# Philippians
# Philippine
Repeat printing string n times (e.g. print ‘hello world’ five times)
printf ‘hello worldn%.0s’ {1..5}
Do not echo the trailing newline
username=`echo -n “bashoneliner”`
Copy a file to multiple files (e.g copy fileA to file(B-D))
tee /dev/null
Delete all non-printing characters
tr -dc ‘[:print:]’ tr –delete ‘n’ output.txt
Replace newline

To uppercase/lowercase

Translate a range of characters (e.g. substitute a-z into a)
echo ‘something’ |tr a-z a
# aaaaaaaaa
Compare two files (e.g. fileA, fileB)
diff fileA fileB
# a: added; d:delete; c:changed

# or
sdiff fileA fileB
# side-to-side merge of file differences
Compare two files, strip trailing carriage return/ nextline (e.g. fileA, fileB)
diff fileA fileB –strip-trailing-cr
Number a file (e.g. fileA)
nl fileA

nl -nrz fileA
# add leading zeros

nl -w1 -s ‘ ‘
# making it simple, blank separate
Join two files field by field with tab (default join by the first column of both file, and default separator is space)
# fileA and fileB should have the same ordering of lines.
join -t ‘t’ fileA fileB

# Join using specified field (e.g. column 3 of fileA and column 5 of fileB)
join -1 3 -2 5 fileA fileB
Combine/ paste two or more files into columns (e.g. fileA, fileB, fileC)
paste fileA fileB fileC
# default tab separate
Group/combine rows into one row
# e.g.
cat filename|paste – –
cat filename|paste – – – –
Fastq to fasta (fastq and fasta are common file formats for bioinformatics sequence data)
cat file.fastq | paste – – – – | sed ‘s/^@/>/g’| cut -f1-2 | tr ‘t’ ‘n’>file.fa
Reverse string

Generate sequence 1-10

Find average of input list/file of integers
i=`wc -l filename|cut -d ‘ ‘ -f1`; cat filename| echo “scale=2;(`paste -sd+`)/”$i|bc
Generate all combination (e.g. 1,2)
echo {1,2}{1,2}
# 1 1, 1 2, 2 1, 2 2
Generate all combination (e.g. A,T,C,G)
for ((i=0; ibasename filename.gz .gz

zcat filename.gz> $(basename filename.gz .gz).unpacked
Add file extension to all file(e.g add .txt)
rename s/$/.txt/ *
# You can use rename -n s/$/.txt/ * to check the result first, it will only print sth like this:
# rename(a, a.txt)
# rename(b, b.txt)
# rename(c, c.txt)
Squeeze repeat patterns (e.g. /t/t –> /t)

Do not print nextline with echo

View first 50 characters of file

Cut and get last column of a file
cat file|rev | cut -d/ -f1 | rev
Add one to variable/increment/ i++ a numeric variable (e.g. $var)
# or

Cut the last column
cat filename|rev|cut -f1|rev
Cat to a file
let me add sth here
exit by control + c
Clear the contents of a file (e.g. filename)

Append to file (e.g. hihi)

Working with json data
#install the useful jq package
#sudo apt-get install jq
#e.g. to get all the values of the ‘url’ key, simply pipe the json to the following jq command(you can use .[]. to select inner json, i.e jq ‘.[].url’)
cat file.json | jq ‘.url’
Decimal to Binary (e.g get binary of 5)
echo -e ${D2B[5]}
echo -e ${D2B[255]}
Wrap each input line to fit in specified width (e.g 4 integers per line)
echo “00110010101110001101” | fold -w4
# 0011
# 0010
# 1011
# 1000
# 1101
Sort a file by column and keep the original order

Right align a column (right align the 2nd column)
cat file.txt|rev|column -t|rev
To both view and store the output
echo ‘hihihihi’ | tee outputfile.txt
# use ‘-a’ with tee to append to file.
Show non-printing (Ctrl) characters with cat

Convert tab to space

Convert space to tab

Display file in octal ( you can also use od to display hexadecimal, decimal, etc)

Reverse cat a file

Reverse the result from uniq -c
while read a b; do yes $b |head -n $a ;done some_commands &>log &

# or
some_commands 2>log &

# or
some_commands 2>&1| tee logfile

# or
some_commands |& tee logfile

# or
some_commands 2>&1 cd tmp/a/b/c
> ||
>mkdir -p tmp/a/b/c
List file type of file (e.g. /tmp/)
file /tmp/
# tmp/: directory
Writing Bash script (‘#!” is called shebang )
# remove string before a “.”
Python simple HTTP Server
python -m SimpleHTTPServer
# or when using python3:
python3 -m http.server
Read user input

declare -a array=()

# or
declare array=()

# or associative array
declare -A array=()
Send a directory
scp -r directoryname user@ip:/path/to/send
Fork bomb
# Don’t try this at home!
# It is a function that calls itself twice every call until you run out of system resources.
# A ‘# ‘ is added in front for safety reason, remove it when seriously you are testing it.
# :(){:|:&};:
Use the last argument

Check last exit code

Extract .xz
unxz filename.tar.xz
# then
tar -xf filename.tar

Unzip tar.bz2 file (e.g. file.tar.bz2)

Unzip tar.xz file (e.g. file.tar.xz)
unxz file.tar.xz
tar xopf file.tar
Extract to a path
tar xvf -C /path/to/directory filename.gz
Zip the content of a directory without including the directory itself
# First cd to the directory, they run:
zip -r -D ../myzipfile .
# you will see the in the parent directory (cd ..)
Output a y/n repeatedly until killed
# ‘y’:

# or ‘n’:
yes n

# or ‘anything’:
yes anything

# pipe yes to other command
yes | rm -r large_directory
Create large dummy file of certain size instantly (e.g. 10GiB)
fallocate -l 10G 10Gigfile
Create dummy file of certain size (e.g. 200mb)
dd if=/dev/zero of=//dev/shm/200m bs=1024k count=200
# or
dd if=/dev/zero of=//dev/shm/200m bs=1M count=200

# Standard output:
# 200+0 records in
# 200+0 records out
# 209715200 bytes (210 MB) copied, 0.0955679 s, 2.2 GB/s
Keep /repeatedly executing the same command (e.g Repeat ‘wc -l filename’ every 1 second)
watch -n 1 wc -l filename
Print commands and their arguments when execute (e.g. echo expr 10 + 20 )
set -x; echo `expr 10 + 20 `
Print some meaningful sentences to you (install fortune first)

Colorful (and useful) version of top (install htop first)

Press any key to continue
read -rsp $’Press any key to continue…n’ -n1 key
Run sql-like command on files from terminal
# download:
# example:
q -d “,” “select c3,c4,c5 from /path/to/file.txt where c3=’foo’ and c5=’boo'”
Using Screen for multiple terminal sessions
# Create session and attach:

# Create a screen and name it ‘test’
screen -S test

# Create detached session foo:
screen -S foo -d -m

# Detached session foo:
screen: ^a^d

# List sessions:
screen -ls

# Attach last session:
screen -r

# Attach to session foo:
screen -r foo

# Kill session foo:
screen -r foo -X quit

# Scroll:
# Hit your screen prefix combination (C-a / control+A), then hit Escape.
# Move up/down with the arrow keys (↑ and ↓).

# Redirect output of an already running process in Screen:
# (C-a / control+A), then hit ‘H’

# Store screen output for Screen:
# Ctrl+A, Shift+H
# You will then find a screen.log file under current directory.
Using Tmux for multiple terminal sessions

Read More
Share this on to discuss with people on this topicSign up on now if you’re not registered yet.



Hey! look, i give tutorials to all my users and i help them!Bio: About:

Leave a Reply

Your email address will not be published. Required fields are marked *