Bash-Oneliner

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, RedHat and 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

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.
Run history number (e.g. 53)
!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'
^aaa^bbb

#echo 'bbb'
#bbb

#Notice that only the first aaa will be replaced, if you want to replace all 'aaa', use ':&' to repeat it:
^aaa^bbb^:&
#or
!!:gs/aaa/bbb/

Run past command that began with (e.g. cat filename)
!cat
# or
!c
# run cat filename again
Bash globbing
# '*' serves as a "wild card" for filename expansion.
/b?n/?at      #/bin/cat

# '?' serves as a single-character "wild card" for filename expansion.
/etc/pa*wd    #/etc/passwd

# ‘[]’ 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

Grep

[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 -c "^$"
Grep and return only integer
grep -o '[0-9]*'
#or
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 '\btarget\b'
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’)
grep -o 'S.*'
Extract text between words (e.g. w1,w2)
grep -o -P '(?<=w1).*(?=w2)'
Grep lines without word (e.g. ‘bbo’)
grep -v bbo filename
Grep lines not begin with string (e.g. #)
grep -v '^#' file.txt
Grep variables with space within it (e.g. myvar=”some strings”)
grep "$myvar" filename
#remember to quote the variable!
Grep only one/first match (e.g. ‘bbo’)
grep -m 1 bbo filename
Grep and return number of matching line(e.g. ‘bbo’)
grep -c bbo filename
Count occurrence (e.g. three times a line count three times)
grep -o bbo filename |wc -l
Case insensitive grep (e.g. ‘bbo’/’BBO’/’Bbo’)
grep -i "bbo" filename
COLOR the match (e.g. ‘bbo’)!
grep --color bbo filename
Grep search all files in a directory(e.g. ‘bbo’)
grep -R bbo /path/to/directory
# or
grep -r bbo /path/to/directory
Search all files in directory, do not ouput the filenames (e.g. ‘bbo’)
grep -rh bbo /path/to/directory
Search all files in directory, output ONLY the filenames with matches(e.g. ‘bbo’)
grep -rl bbo /path/to/directory
Grep OR (e.g. A or B or C or D)
grep 'A\|B\|C\|D'
Grep AND (e.g. A and B)
grep 'A.*B'
Regex any singer character (e.g. ACB or AEB)
grep 'A.B'
Regex with or without a certain character (e.g. color or colour)
grep ‘colou?r’
Grep all content of a fileA from fileB
grep -f fileA fileB
Grep a tab
grep $'\t'
Grep variable from variable
$echo "$long_str"|grep -q "$short_str"
if [ $? -eq 0 ]; then echo 'found'; fi
#grep -q will output 0 if match found
#remember to add space between []!
Grep strings between a bracket()
grep -oP '\(\K[^\)]+'
Grep number of characters with known strings in between(e.g. AAEL000001-RA)
grep -o -w "\w\{10\}\-R\w\{1\}"
# \w word character [0-9a-zA-Z_] \W not word character
Skip directory (e.g. ‘bbo’)
grep -d skip 'bbo' /path/to/files/*

Sed

[back to top]

Remove the 1st line
sed 1d filename
Remove the first 100 lines (remove line 1-100)
sed 1,100d filename
Remove lines with string (e.g. ‘bbo’)
sed "/bbo/d" filename
- case insensitive:
sed "/bbo/Id" filename
Remove lines whose nth character not equal to a value (e.g. 5th character not equal to 2)
sed -E '/^.{5}[^2]/d'
#aaaa2aaa (you can stay)
#aaaa1aaa (delete!)
Edit infile (edit and save to file), (e.g. deleting the lines with ‘bbo’ and save to file)
sed -i "/bbo/d" filename
When using variable (e.g. $i), use double quotes “ “
# e.g. add >$i to the first line (to make a bioinformatics FASTA file)
sed "1i >$i"
# notice the double quotes! in other examples, you can use a single quote, but here, no way!
# '1i' means insert to first line
Using environment variable and end-of-line pattern at the same time.
# Use backslash for end-of-line $ pattern, and double quotes for expressing the variable
sed -e "\$s/\$/\n+--$3-----+/"
Delete/remove empty lines
sed '/^\s*$/d'

# or

sed '/^$/d'
Delete/remove last line
sed '$d'
Delete/remove last character from end of file
sed -i '$ s/.$//' filename
Add string to beginning of file (e.g. “[”)
sed -i '1s/^/[/' file
Add string at certain line number (e.g. add ‘something’ to line 1 and line 3)
sed -e '1isomething -e '3isomething'
Add string to end of file (e.g. “]”)
sed '$s/$/]/' filename
Add newline to the end
sed '$a\'
Add string to beginning of every line (e.g. ‘bbo’)
sed -e 's/^/bbo/' file
Add string to end of each line (e.g. “}”)
sed -e 's/$/\}\]/' filename
Add \n every nth character (e.g. every 4th character)
sed 's/.\{4\}/&\n/g'
Concatenate/combine/join files with a seperator and next line (e.g separate by “,”)
sed -s '$a,' *.json > all.json
Substitution (e.g. replace A by B)
sed 's/A/B/g' filename
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’)
sed -n '/^@S/p'
Delete lines with string (e.g. ‘bbo’)
sed '/bbo/d' filename
Print/get/trim a range of line (e.g. line 500-5000)
sed -n 500,5000p filename
sed -n '0~3p' filename

# catch 0: start; 3: step
sed -n '1~2p'
sed -n '1p;0~3p'
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
sed 's/,$//g'
Add a column to the end
sed "s/$/\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/*./}/" $i;done >T000086_1.02.np
Remove newline\ nextline
sed ':a;N;$!ba;s/\n//g'
sed -n -e '123p'
sed -n '10,33p' <filename
Change delimiter
sed 's=/=\\/=g'
Replace with wildcard (e.g A-1-e or A-2-e or A-3-e….)
sed 's/A-.*-e//g' filename
Remove last character of file
sed '$ s/.$//'
Insert character at specified position of file (e.g. AAAAAA –> AAA#AAA)
sed -r -e 's/^.{3}/&#/' file

Awk

[back to top]

Set tab as field separator
awk -F $'\t'
Output as tab separated (also as field separator)
awk -v OFS='\t'
Pass variable
a=bbo;b=obb;
awk -v a="$a" -v b="$b" "$1==a && $10=b" filename
awk '{print NR,length($0);}' filename
Find number of columns
awk '{print NF}'
Reverse column order
awk '{print $2, $1}'
Check if there is a comma in a column (e.g. column $1)
awk '$1~/,/ {print}'
Split and do for loop
awk '{split($2, a,",");for (i in a) print $1"\t"a[i]}' filename
awk -v N=7 '{print}/bbo/&& --N<=0 {exit}'
ls|xargs -n1 -I file awk '{s=$0};END{print FILENAME,s}' file
Add string to the beginning of a column (e.g add “chr” to column $3)
awk 'BEGIN{OFS="\t"}$3="chr"$3'
Remove lines with string (e.g. ‘bbo’)
awk '!/bbo/' file
Remove last column
awk 'NF{NF-=1};1' file
Usage and meaning of NR and FNR
# For example there are two files:
# fileA:
# a
# b
# c
# fileB:
# d
# e
awk 'print FILENAME, NR,FNR,$0}' fileA fileB
# fileA    1    1    a
# fileA    2    2    b
# fileA    3    3    c
# fileB    4    1    d
# fileB    5    2    e
AND gate
# For example there are two files:
# fileA:
# 1    0
# 2    1
# 3    1
# 4    0
# fileB:
# 1    0
# 2    1
# 3    0
# 4    1

awk -v OFS='\t' 'NR=FNR{a[$1]=$2;next} NF {print $1,((a[$1]=$2)? $2:"0")}' fileA fileB
# 1    0
# 2    1
# 3    0
# 4    0
Round all numbers of file (e.g. 2 significant figure)
awk '{while (match($0, /[0-9]+\[0-9]+/)){
    \printf "%s%.2f", substr($0,0,RSTART-1),substr($0,RSTART,RLENGTH)
    \$0=substr($0, RSTART+RLENGTH)
    \}
    \print
    \}'
Give number/index to every row
awk '{printf("%s\t%s\n",NR,$0)}'
Break combine column data into rows
# For example, seperate the following content:
# David    cat,dog
# into
# David    cat
# David    dog

awk '{split($2,a,",");for(i in a)print $1"\t"a[i]}' file

# Detail here: http://stackoverflow.com/questions/33408762/bash-turning-single-comma-separated-column-into-multi-line-string
Average a file (each line in file contains only one number)
awk '{s+=$1}END{print s/NR}'
awk '$1 ~ /^Linux/'
Sort a row (e.g. 1 40 35 12 23 –> 1 12 23 35 40)
awk ' {split( $0, a, "\t" ); asort( a ); for( i = 1; i <= length(a); i++ ) printf( "%s\t", a[i] ); printf( "\n" ); }'
Subtract previous row values (add column6 which equal to column4 minus last column5)
awk '{$6 = $4 - prev5; prev5 = $5; print;}'

Xargs

[back to top]

Set tab as delimiter (default:space)
xargs -d\t
Display 3 items per line
echo 1 2 3 4 5 6| xargs -n 3
# 1 2 3
# 4 5 6

Prompt before execution
echo a b c |xargs -p -n 3
xargs -t abcd
# bin/echo abcd
# abcd

With find and rm
find . -name "*.html"|xargs rm

# when using a backtick
rm `find . -name "*.html"`
Delete files with whitespace in filename (e.g. “hello 2001”)
find . -name "*.c" -print0|xargs -0 rm -rf
Show limits on command-line length
xargs --show-limits
# Output from my Ubuntu:
# Your environment variables take up 3653 bytes
# POSIX upper limit on argument length (this system): 2091451
# POSIX smallest allowable upper limit on argument length (all systems): 4096
# Maximum length of command we could actually use: 2087798
# Size of command buffer we are actually using: 131072
# Maximum parallelism (--max-procs must be no greater): 2147483647
Move files to folder
find . -name "*.bak" -print 0|xargs -0 -I {} mv {} ~/old

# or
find . -name "*.bak" -print 0|xargs -0 -I file mv file ~/old
Move first 100th files to a directory (e.g. d1)
ls |head -100|xargs -I {} mv {} d1
Parallel
time echo {1..5} |xargs -n 1 -P 5 sleep

# a lot faster than:
time echo {1..5} |xargs -n1 sleep
Copy all files from A to B
find /dir/to/A -type f -name "*.py" -print 0| xargs -0 -r -I file cp -v -p file --target-directory=/path/to/B

# v: verbose|
# p: keep detail (e.g. owner)

With sed
ls |xargs -n1 -I file sed -i '/^Pos/d' filename
Add the file name to the first line of file
ls |sed 's/.txt//g'|xargs -n1 -I file sed -i -e '1 i\>file\' file.txt
Count all files
ls |xargs -n1 wc -l
Turn output into a single line
ls -l| xargs
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
ls|xargs wc -l
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 '192.168.1.111' /etc | xargs sed -i 's/192.168.1.111/192.168.2.111/g'

Find

[back to top]

List all sub directory/file in the current directory
find .
List all files under the current directory
find . -type f
List all directories under the current directory
find . -type d
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 "%f\n"
Find and delete file with size less than (e.g. 74 byte)
find . -name "*.mso" -size -74c -delete

# M for MB, etc

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

# if variable is null
if [ ! -s "myvariable" ]
#True of the length if "STRING" is zero.

# Test if file exist
if [ -e 'filename' ]
then
  echo -e "file exists!"
fi

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

# Test if the value of x is greater or equal than 5
if [ "$x" -ge 5 ]; then# Test if the value of x is greater or equal than 5, in bash/ksh/zsh:
if ((x >= 5)); then# Use (( )) for arithmetic operation
if ((j==u+2))

# Use [[ ]] for comparison
if [[ $age -gt 21 ]]

More if commands

For loop
for i in $(ls); do echo file $i;done
#or
for i in *; do echo file $i; done

# Press any key to continue each loop
for i in $(cat tpc_stats_0925.log |grep failed|grep -o '\query\w\{1,2\}');do cat ${i}.log; read -rsp $'Press any key to continue...\n' -n1 key;done

# Print a file line by line when a key is pressed,
oifs="$IFS"; IFS=$'\n'; for line in $(cat myfile); do ...; done
while read -r line; do ...; done <myfile

#If only one word a line, simply
for line in $(cat myfile); do echo $line; read -n1; done

#Loop through an array
for i in "${arrayName[@]}"; do echo $i;done

While loop,
# Column subtraction of a file (e.g. a 3 columns file)
while read a b c; do echo $(($c-$b));done < <(head filename)
#there is a space between the two '<'s

# Sum up column subtraction
i=0; while read a b c; do ((i+=$c-$b)); echo $i; done < <(head filename)

# Keep checking a running process (e.g. perl) and start another new process (e.g. python) immediately after it. (BETTER use the wait command! Ctrl+F 'wait')
while [[ $(pidof perl) ]];do echo f;sleep 10;done && python timetorunpython.py
switch (case in bash)
read type;
case $type in
  '0')
    echo 'how'
    ;;
  '1')
    echo 'are'
    ;;
  '2')
    echo 'you'
    ;;
esac

Variable

[back to top]

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

# 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 )
var="0050"
echo ${var[@]#0}
#050
Replacement (e.g. replace ‘a’ with ‘,’)
{var/a/,}
Replace all (e.g. replace all ‘a’ with ‘,’)
{var//a/,}
#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)
var=HelloWorld
echo ${var,,}
helloworld
Expand and then execute variable/argument
cmd="bar=foo"
eval "$cmd"
echo "$bar" # foo

Math

[back to top]

Arithmetic Expansion in Bash (Operators: +, -, *, /, %, etc)
echo $(( 10 + 5 ))  #15
x=1
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
x=2
y=3
echo $(( x ** y )) #8
factor 50
# 50: 2 5 5
Sum up input list (e.g. seq 10)
seq 10|paste -sd+|bc
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
#.66

# Exponent operator
echo "10^2" | bc
#100

# Using variables
echo "var=5;--var"| bc
#4

Time

[back to top]

Find out the time require for executing a command
time echo hi
Wait for some time (e.g 10s)
sleep 10

# wait for random duration (e.g. sleep 1-5 second, like adding a jitter)
sleep $[ ( $RANDOM % 5 ) + 1 ]
Log out your account after a certain period of time (e.g 10 seconds)
TMOUT=10
#once you set this variable, logout timer start running!
Set how long you want to run a command
#This will run the command 'sleep 10' for only 1 second.
timeout 1 sleep 10
Set when you want to run a command (e.g 1 min from now)
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> <EOT>   # press Ctrl + D to exit
job 1 at Wed Apr 18 11:16:00 2018

Download

[back to top]

Download the content of this README.md (the one your are viewing now)
curl https://raw.githubusercontent.com/onceupon/Bash-Oneliner/master/README.md | pandoc -f markdown -t man | man -l -

# or w3m (a text based web browser and pager)
curl https://raw.githubusercontent.com/onceupon/Bash-Oneliner/master/README.md | pandoc | w3m -T text/html

# or using emacs (in emac text editor)
emacs --eval '(org-mode)' --insert <(curl https://raw.githubusercontent.com/onceupon/Bash-Oneliner/master/README.md | pandoc -t org)

# or using emacs (on terminal, exit using Ctrl + x then Ctrl + c)
emacs -nw --eval '(org-mode)' --insert <(curl https://raw.githubusercontent.com/onceupon/Bash-Oneliner/master/README.md | pandoc -t org)
Download all from a page
wget -r -l1 -H -t1 -nd -N -np -A mp3 -e robots=off http://example.com

# -r: recursive and download all links on page
# -l1: only one level link
# -H: span host, visit other hosts
# -t1: numbers of retries
# -nd: don't make new directories, download to here
# -N: turn on timestamp
# -nd: no parent
# -A: type (separate by ,)
# -e robots=off: ignore the robots.txt file which stop wget from crashing the site, sorry example.com
Upload a file to web and download (https://transfer.sh/)
#  Upload a file (e.g. filename.txt):
curl --upload-file ./filename.txt https://transfer.sh/filename.txt
# the above command will return a URL, e.g: https://transfer.sh/tG8rM/filename.txt

# Next you can download it by:
curl https://transfer.sh/tG8rM/filename.txt -o filename.txt
Download file if necessary
data=file.txt
url=http://www.example.com/$data
if [ ! -s $data ];then
    echo "downloading test data..."
    wget $url
fi
Wget to a filename (when a long name)
wget -O filename "http://example.com"
Wget files to a folder
wget -P /path/to/directory "http://example.com"
Instruct curl to follow any redirect until it reaches the final destination:
curl -L google.com

Random

[back to top]

Random generate password (e.g. generate 5 password each of length 13)
sudo apt install pwgen
pwgen 13 5
#sahcahS9dah4a xieXaiJaey7xa UuMeo0ma7eic9 Ahpah9see3zai acerae7Huigh7
Random pick 100 lines from a file
shuf -n 100 filename
Random order (lucky draw)
for i in a b c d e; do echo $i; done| shuf
Echo series of random numbers between a range (e.g. shuffle numbers from 0-100, then pick 15 of them randomly)
shuf -i 0-100 -n 15
Echo a random number
echo $RANDOM
Random from 0-9
echo $((RANDOM % 10))
Random from 1-10
echo $(((RANDOM %10)+1))

Xwindow

[back to top]

X11 GUI applications! Here are some GUI tools for you if you get bored by the text-only environment.

Enable X11 forwarding,in order to use graphical application on servers
ssh -X user_name@ip_address

# or setting through xhost
# --> Install the following for Centos:
# xorg-x11-xauth
# xorg-x11-fonts-*
# xorg-x11-utils
Little xwindow tools
xclock
xeyes
xcowsay
Open pictures/images from ssh server
1. ssh -X user_name@ip_address
2. apt-get install eog
3. eog picture.png
Watch videos on server
1. ssh -X user_name@ip_address
2. sudo apt install mpv
3. mpv myvideo.mp4
Use gedit on server (GUI editor)
1. ssh -X user_name@ip_address
2. apt-get install gedit
3. gedit filename.txt
Open PDF file from ssh server
1. ssh -X user_name@ip_address
2. apt-get install evince
3. evince filename.pdf
Use google-chrome browser from ssh server
1. ssh -X user_name@ip_address
2. apt-get install libxss1 libappindicator1 libindicator7
3. wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
4. sudo apt-get install -f
5. dpkg -i google-chrome*.deb
6. google-chrome

System

[back to top]

Audit files to see who made changes to a file [RedHat based system only]
# To audit a directory recursively for changes (e.g. myproject)
auditctl -w /path/to/myproject/ -p wa

# If you delete a file name "VIPfile", the deletion is recorded in /var/log/audit/audit.log
sudo grep VIPfile /var/log/audit/audit.log
#type=PATH msg=audit(1581417313.678:113): item=1 name="VIPfile" inode=300115 dev=ca:01 mode=0100664 ouid=1000 ogid=1000 rdev=00:00 nametype=DELETE cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0
Check out whether SELinux is enabled
sestatus
# SELinux status:                 enabled
# SELinuxfs mount:                /sys/fs/selinux
# SELinux root directory:         /etc/selinux
# Loaded policy name:             targeted
# Current mode:                   enforcing
# Mode from config file:          enforcing
# Policy MLS status:              enabled
# Policy deny_unknown status:     allowed
# Max kernel policy version:      31
Generate public key from private key
ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub
Copy your default public key to remote user
ssh-copy-id <user_name>@<server_IP>
# then you need to enter the password
# and next time you won't need to enter password when ssh to that user
Copy default public key to remote user using the required private key (e.g. use your mykey.pem key to copy your id_rsa.pub to the remote user)
# before you need to use mykey.pem to ssh to remote user.
ssh-copy-id -i ~/.ssh/id_rsa.pub -o "IdentityFile ~/Downloads/mykey.pem" <user_name>@<server_IP>
# now you don't need to use key to ssh to that user.
SSH Agent Forwarding
# To bring your key with you when ssh to serverA, then ssh to serverB from serverA using the key.
ssh-agent
ssh-add /path/to/mykey.pem
ssh -A <username>@<IP_of_serverA>
# Next you can ssh to serverB
ssh <username>@<IP_of_serverB>
Follow the most recent logs from service
journalctl -u <service_name> -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 <zombie_PID>
# Then you can kill its parent and you will notice the zombie is gone.
sudo kill 9 <parent_PID>
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)
iftop -i enp175s0f0
Tell how long the system has been running and number of users
uptime
Check if it’s root running
if [ "$EUID" -ne 0 ]; then
        echo "Please run this as root"
        exit 1
fi
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
exit
Display file status (size; access, modify and change time, etc) of a file (e.g. filename.txt)
stat filename.txt
Snapshot of the current processes
ps aux
Display a tree of processes
pstree
Find maximum number of processes
cat /proc/sys/kernel/pid_max
dmesg
Show IP address
$ip add show

# or
ifconfig
runlevel

# or
who -r
Change SysV runlevel (e.g. 5)
init 5
#or
telinit 5
Display all available services in all runlevels,
chkconfig --list
# update-rc.d equivalent to chkconfig in ubuntu
Check system version
cat /etc/*-release
Linux Programmer’s Manuel: hier- description of the filesystem hierarchy
man hier
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
jobs -l
Run a program with modified priority (e.g. ./test.sh)
# 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 ./test.sh
Export PATH
export PATH=$PATH:~/path/you/want
Make file executable
chmod +x filename
# you can now ./filename to execute it
uname -a

# Check system hardware-platform (x86-64)
uname -i
Surf the net
links www.google.com
Add user, set passwd
useradd username
passwd username
Edit variable for bash, (e.g. displaying the whole path)
1. joe ~/.bash_profile
2. export PS1='\u@\h:\w\$'
# $PS1 is a variable that defines the makeup and style of the command prompt
3. source ~/.bash_profile
Edit environment setting (e.g. alias)
1. joe ~/.bash_profile
2. alias pd="pwd" //no more need to type that 'w'!
3. source ~/.bash_profile
alias -p
Unalias (e.g. after alias ls=’ls –color=auto’)
unalias ls
Set and unset shell options
# print all shell options
shopt

# 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
env
Unset environment variable (e.g. unset variable ‘MYVAR’)
unset MYVAR
Show partition format
lsblk
Inform the OS of partition table changes
partprobe
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
rsh node_name
Check port (active internet connection)
netstat -tulpn
readlink filename
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
declare -F
List total size of a directory
du -hs .

# or
du -sb
Copy directory with permission setting
cp -rp /path/to/directory
Store current directory
pushd .

# then pop
popd

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

# or
du -h

#or
du -sk /var/log/* |sort -rn |head -10
Show all file system type
df -TH
Show current runlevel
runlevel
Switch runlevel
init 3

#or
telinit 3
Permanently modify runlevel
1. edit /etc/init/rc-sysinit.conf
2. env DEFAULT_RUNLEVEL=2
Become root
su
Become somebody
su somebody
Report user quotes on device
repquota -auvs
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
mount
# or
df
List current usernames and user-numbers
cat /etc/passwd
Get all username
getent passwd| awk '{FS="[:]"; print $1}'
Show all users
compgen -u
Show all groups
compgen -g
Show group of user
group username
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!"
    exit;
fi
# 'id -u' output 0 if it's not root
Find out CPU information
more /proc/cpuinfo

# or
lscpu
Set quota for user (e.g. disk soft limit: 120586240; hard limit: 125829120)
setquota username 120586240 125829120 0 0 /home
Show quota for user
quota -v username
Display current libraries from the cache
ldconfig -p
ldd /bin/ls
Check user login
lastlog
Check last reboot history
last reboot
Edit path for all users
joe /etc/environment
# edit this file
Show and set user limit
ulimit -u
Which ports are listening for TCP connections from the network
nmap -sT -O localhost
#notice that some companies might not like you using nmap
nproc --all
Check status of each core
1. top
2. press '1'
Show jobs and PID
jobs -l
List all running services
service --status-all
Schedule shutdown server
shutdown -r +5 "Server will restart in 5 minutes. Please save your work."
Cancel scheduled shutdown
shutdown -c
Broadcast to all users
wall -n hihi
Kill all process of a user
pkill -U user_name
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:
hostnamectl
# Or check /etc/hostname

# If still not working..., edit:
/etc/sysconfig/network
/etc/sysconfig/network-scripts/ifcfg-ensxxx
#add HOSTNAME="your-new-hostname"
List installed packages
apt list --installed

# or on Red Hat:
yum list installed
Check which file make the device busy on umount
lsof /mnt/dir
When sound not working
killall pulseaudio
# then press Alt-F2 and type in pulseaudio
When sound not working
killall pulseaudio
List information about SCSI devices
lsscsi
Tutorial for setting up your own DNS server

http://onceuponmine.blogspot.tw/2017/08/set-up-your-own-dns-server.html

Tutorial for creating a simple daemon

http://onceuponmine.blogspot.tw/2017/07/create-your-first-simple-daemon.html

Tutorial for using your gmail to send email

http://onceuponmine.blogspot.tw/2017/10/setting-up-msmtprc-and-use-your-gmail.html

##### Using telnet to test open ports, test if you can connect to a port (e.g 53) of a server (e.g 192.168.2.106)

telnet 192.168.2.106 53
Change network maximum transmission unit (mtu) (e.g. change to 9000)
ifconfig eth0 mtu 9000
Get pid of a running process (e.g python)
pidof python

# or
ps aux|grep python
NTP
# Start ntp:
ntpd

# 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)
pvscan
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 <package_name>
sudo dpkg --purge <package_name>
Create a ssh tunnel
ssh -f -L 9000:targetservername:8088 root@192.168.14.72 -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 192.168.14.72
#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
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.

Show a listing of last logged in users.
lastb
Show a listing of current logged in users, print information of them
who
Show who is logged on and what they are doing
w
users
Stop tailing a file on program terminate
tail -f --pid=<PID> filename.txt
# replace <PID> with the process ID of the program.
List all enabled services
systemctl list-unit-files|grep enabled

Hardware

[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
sudo dmidecode -t memory
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)
blkid /dev/sdb
Generate an UUID
uuidgen
lsblk -io KNAME,TYPE,MODEL,VENDOR,SIZE,ROTA
#where ROTA means rotational device / spinning hard disks (1 if true, 0 if false)
List all PCI (Peripheral Component Interconnect) devices
lspci
# List information about NIC
lspci | egrep -i --color 'network|ethernet'
List all USB devices
lsusb
Linux modules
# Show the status of modules in the Linux Kernel
lsmod

# Add and remove modules from the Linux Kernel
modprobe

# or
# Remove a module
rmmod

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

# Remotely switching on server
ipmitool -U <bmc_username> -P <bmc_password> -I lanplus -H <bmc_ip_address> 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 192.168.0.55
ipmitool -I bmc lan set 1 netmask 255.255.255.0
ipmitool -I bmc lan set 1 defgw ipaddr 192.168.0.1

Networking

[back to top]

Resolve a domain to an IP address in a Bash script?
dig +short www.example.com
Show the SSL certificate of a domain
openssl s_client -showcerts -connect www.example.com:443
Display IP address
ip a
Display route table
ip r
Display ARP cache (ARP cache displays the MAC addresses of device in the same network that you have connected to)
ip n
Add transient IP addres (reset after reboot) (e.g. add 192.168.140.3/24 to device eno16777736)
ip address add 192.168.140.3/24 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
sudo nmcli c reload
Restart all interfaces
sudo systemctl restart network.service
To view hostname, OS, kernal, architecture at the same time!
hostnamectl
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://example.com/
# 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

Data wrangling

[back to top]

# 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 world\n%.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 <fileA fileB fileC fileD >/dev/null
Remove newline / nextline
tr --delete '\n' <input.txt >output.txt
Replace newline
tr '\n' ' ' <filename
To uppercase/lowercase
tr /a-z/ /A-Z/
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

#or
nl -nrz fileA
# add leading zeros

#or
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.
# AAAA
# BBBB
# CCCC
# DDDD
cat filename|paste - -
# AAAABBBB
# CCCCDDDD
cat filename|paste - - - -
# AAAABBBBCCCCDDDD
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
echo 12345| rev
Generate sequence 1-10
seq 10
Find average of input list/file of integers
i=`wc -l filename|cut -d ' ' -f1`; cat filename| echo "scale=2;(`paste -sd+`)/"$i|bc
Generate all combination (e.g. 1,2)
echo {1,2}{1,2}
# 1 1, 1 2, 2 1, 2 2
Generate all combination (e.g. A,T,C,G)
set = {A,T,C,G}
group= 5
for ((i=0; i<$group; i++));do
    repetition=$set$repetition;done
    bash -c "echo "$repetition""
Read file content to variable
foo=$(<test1)
Echo size of variable
echo ${#foo}
Echo a tab
echo -e ' \t '
Split file into smaller file
# Split by line (e.g. 1000 lines/smallfile)
split -d -l 1000 largefile.txt

# Split by byte without breaking lines across files
split -C 10 largefile.txt
Create a large amount of dummy files (e.g 100000 files, 10 bytes each):
#1. Create a big file
dd if=/dev/zero of=bigfile bs=1 count=1000000

#2. Split the big file to 100000 10-bytes files
 split -b 10 -a 10 bigfile
Rename all files (e.g. remove ABC from all .gz files)
rename 's/ABC//' *.gz
Remove file extension (e.g remove .gz from filename.gz)
basename 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)
tr -s "/t" < filename
Do not print nextline with echo
echo -e 'text here \c'
View first 50 characters of file
head -c 50 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. $var)
((var++))
# or
var=$((var+1))

Cut the last column
cat filename|rev|cut -f1|rev
Cat to a file
cat >myfile
let me add sth here
exit by control + c
^C
Clear the contents of a file (e.g. filename)
>filename
Append to file (e.g. hihi)
echo 'hihi' >>filename
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)
D2B=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})
echo -e ${D2B[5]}
#00000101
echo -e ${D2B[255]}
#11111111
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
sort -k3,3 -s
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
cat -v filename
Convert tab to space
expand filename
Convert space to tab
unexpand filename
Display file in octal ( you can also use od to display hexadecimal, decimal, etc)
od filename
Reverse cat a file
tac filename
Reverse the result from uniq -c
while read a b; do yes $b |head -n $a ;done <test.txt

Others

[back to top]

Describe the format and characteristics of image files.
identify myimage.png
#myimage.png PNG 1049x747 1049x747+0+0 8-bit sRGB 1.006MB 0.000u 0:00.000
Bash auto-complete (e.g. show options “now tomorrow never” when you press’tab’ after typing “dothis”)

More examples

complete -W "now tomorrow never" dothis
# ~$ dothis  
# never     now       tomorrow
# press 'tab' again to auto-complete after typing 'n' or 't'
Displays a calendar
# print the current month, today will be highlighted.
cal
# October 2019      
# Su Mo Tu We Th Fr Sa  
#    1  2  3  4  5  
# 6  7  8  9 10 11 12  
# 13 14 15 16 17 18 19  
# 20 21 22 23 24 25 26  
# 27 28 29 30 31  

# only display November
cal -m 11
Forces applications to use the default language for output
export LC_ALL=C

# to revert:
unset LC_ALL
Encode strings as Base64 strings
echo test|base64
#dGVzdAo=
Get parent directory of current directory
dirname `pwd`
Read .gz file without extracting
zmore filename

# or
zless filename
Run command in background, output error file
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 >>outfile
#0: standard input; 1: standard output; 2: standard error
Run multiple commands in background
# run sequentially
(sleep 2; sleep 3) &

# run parallelly
sleep 2 & sleep 3 &
Run process even when logout (immune to hangups, with output to a non-tty)
# e.g. Run myscript.sh even when log out.
nohup bash myscript.sh
Send mail
echo 'heres the content'| mail -a /path/to/attach_file.txt -s 'mail.subject' me@gmail.com
# use -a flag to set send from (-a "From: some@mail.tld")
Convert .xls to csv
xls2csv filename
Make BEEP sound
speaker-test -t sine -f 1000 -l1
Set beep duration
(speaker-test -t sine -f 1000) & pid=$!;sleep 0.1s;kill -9 $pid
Editing your history
history -w
vi ~/.bash_history
history -r

#or
history -d [line_number]
Interacting with history
# list 5 previous command (similar to `history |tail -n 5` but wont print the history command itself)
fc -l -5
Delete current bash command
Ctrl+U

# or
Ctrl+C

# or
Alt+Shift+#
# to make it to history
Add something to history (e.g. “addmetohistory”)
# addmetodistory
# just add a "#" before~~
Get last history/record filename
head !$
Clean screen
clear
# or simply Ctrl+l
Backup with rsync
rsync -av filename filename.bak
rsync -av directory directory.bak
rsync -av --ignore_existing directory/ directory.bak
rsync -av --update directory directory.bak

rsync -av directory user@ip_address:/path/to/directory.bak
# skip files that are newer on receiver (i prefer this one!)
Make all directories at one time!
mkdir -p project/{lib/ext,bin,src,doc/{html,info,pdf},demo/stat}
# -p: make parent directory
# this will create project/doc/html/; project/doc/info; project/lib/ext ,etc
Run command only if another command returns zero exit status (well done)
cd tmp/ && tar xvf ~/a.tar
Run command only if another command returns non-zero exit status (not finish)
cd tmp/a/b/c ||mkdir -p tmp/a/b/c
Use backslash “" to break long command
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 )
#!/bin/bash
file=${1#*.}
# remove string before a "."
Python simple HTTP Server
python -m SimpleHTTPServer
# or when using python3:
python3 -m http.server
Read user input
read input
echo $input
Array
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
echo $?
Extract .xf
unxz filename.tar.xz
# then
tar -xf filename.tar
Unzip tar.bz2 file (e.g. file.tar.bz2)
tar xvfj 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
Output a y/n repeatedly until killed
# 'y':
yes

# or 'n':
yes n

# or 'anything':
yes anything

# For example:
```bash
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
set -x; echo `expr 10 + 20 `
fortune
Colorful (and useful) version of top (install htop first)
htop
Press any key to continue
read -rsp $'Press any key to continue...\n' -n1 key
Run sql-like command on files from terminal
# download:
# https://github.com/harelba/q
# 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:
screen

# 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
# Create session and attach:
tmux

# Attach to session foo:
tmux attach -t foo

# Detached session foo:
^bd

# List sessions:
tmux ls

# Attach last session:
tmux attach

# Kill session foo:
tmux kill-session -t foo

# Create detached session foo:
tmux new -s foo -d

# Send command to all panes in tmux:
Ctrl-B
:setw synchronize-panes

# Some tmux pane control commands:
Ctrl-B
#   Panes (splits), Press Ctrl+B, then input the following symbol:
#   %  horizontal split
#   "  vertical split
#   o  swap panes
#   q  show pane numbers
#   x  kill pane
#   space - toggle between layouts

#   Distribute Vertically (rows):
select-layout even-vertical
#   or
Ctrl+b, Alt+2

# Distribute horizontally (columns):
select-layout even-horizontal
#   or
Ctrl+b, Alt+1

# Scroll
Ctrl-b then \[ then you can use your normal navigation keys to scroll around.
Press q to quit scroll mode.
Pass password to ssh
sshpass -p mypassword ssh root@10.102.14.88 "df -h"
Wait for a pid (job) to complete
wait %1
# or
wait $PID
wait ${!}
#wait ${!} to wait till the last background process ($! is the PID of the last background process)
Convert pdf to txt
sudo apt-get install poppler-utils
pdftotext example.pdf example.txt
List only directory
ls -ld -- */
Capture/record/save terminal output (capture everything you type and output)
script output.txt
# start using terminal
# to logout the screen session (stop saving the contents), type exit.
List contents of directories in a tree-like format.
tree
# go to the directory you want to list, and type tree (sudo apt-get install tree)
# output:
# home/
# └── project
#     ├── 1
#     ├── 2
#     ├── 3
#     ├── 4
#     └── 5
#

# set level directories deep (e.g. level 1)
tree -L 1
# home/
# └── project
Set up virtualenv(sandbox) for python
# 1. install virtualenv.
sudo apt-get install virtualenv
# 2. Create a directory (name it .venv or whatever name your want) for your new shiny isolated environment.
virtualenv .venv
# 3. source virtual bin
source .venv/bin/activate
# 4. you can check check if you are now inside a sandbox.
type pip
# 5. Now you can install your pip package, here requirements.txt is simply a txt file containing all the packages you want. (e.g tornado==4.5.3).
pip install -r requirements.txt

More coming!!