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shell

variable

  • $variable_name
  • no space around =
  • enclose variable with space with "
    • echo "$variable"

make as variable output

  • var=$(git status)

swallow output

<some command> &> /dev/null

string

concat

allmsg="${allmsg}\n${msg1}\n${msg2}\n${msg3}\n"

slice

for str[1]

echo $str | cut -c2

for str[0:4]

echo $str | cut -c1-4

split

for str.split(',')[0]

echo $str | cut -d ',' -f 1

replace

sed

echo xxx | sed "s/<find>/<replace>/<position>"
sed -i "s/<find>/<replace>/<position>" input.txt

for <position> - g = all - 1 = 1 - 2g = 2:

https://stackoverflow.com/a/44898816/15493213

use \bword\b for whole word

tr

tr 'find' 'replace'

paste

paste -sd'abc'
replace every \n with a b c in a round robin manner

array

arr=((1 2 3))

get index

echo ${arr[2]}

replace

echo ${arr[@]/<find>/<replace>}

awk

awk '{print $1, ":", ($2>=50 && $3>=50 && $4>=50) ? "Pass" : "Fail"}'

awk '{print "2 " $2 " 3 " $3}' file.txt

awk '{avg=($2+$3+$4)/3; print $0, ":", (avg>=80)?"A":(avg>=60)?"B":(avg>=50)?"C":"FAIL"}'

  • substring index
    • awk 'BEGIN{print index("abcdes","bc")}' → 2
    • echo "My name is Deepak" | awk '{print index($0,"Deepak")}' → 12

find

Find all files under the current directory recursively

List all the files named haha

find . -name haha

List all the files > 50MB

find . -size +50M

List all the files < 50MB

find . -size -50M

Delete all the files matching the pattern *pat*

find . -name '*pat*' -delete

scp

remote to local

scp -P <port> <remote username>@<remote host>:path/to/file path/to/file

local to remote 

scp -P <port> path/to/file <remote username>@<remote host>:path/to/file

https://linuxize.com/post/how-to-use-scp-command-to-securely-transfer-files/

processes

output to file

  • write to file
    • echo haha > file.txt
  • append to file
    • echo haha >> file.txt

curl

curl + python to extract json

e.g. 

curl -s "http://ws.audioscrobbler.com/2.0/?method=user.getrec  
enttracks&user=<user>&api_key=<api key>&format=json" | python3 -c "import json,sys;result=json.load(sys.stdin);print(result['recenttracks']['track'][0]['name'])"

disk

  • usage and available space of all partitions
    • df -h
  • size of all top level non-hidden directories or files
    • du -sh *
    • du -sh * | sort -h
      • sorted
    • du -sh * | sort -rh
      • reversly sorted
    • du -sh -I fileprefix* *
      • exclude fileprefix*
  • size of all top level directories or files
    • du -ahd1 . | sort -h
  • df -i
  • df -ah

sort

  • sort -n for numerial sort
  • sort -r for reverse
  • sort -k 2 to sort with 2nd column

alias

  • double quote -> evaluate at creation time
    • shell-1.png
  • single quote -> evaluate at runtime
    • shell-2.png

tar

  • compress
    • compress b08901001_pa1 to b08901001_pa1.tgz
      • tar -zcvf b08901001_pa1.tgz b08901001_pa1
  • extract
    • extract sample.tgz
      • tar zxvf sample.tgz
    • extract sample.tgz into an existing directory sample
      • tar zxvf sample.tgz -C sample

zip

  • zip haha to haha.zip
    • zip -r haha.zip haha

find files

fzf

history

  • history to show history
  • !5 to execute 5th commands in history
  • ctrl+r to search history command

commands

memory

free -h

exec time

time command

meta

  • autocomplete from history
    • ctrl+R
  • cd to previous directory
    • cd -
  • softlink
    • ln -s ogfile softlink
    • create a pointer to ogfile
    • deleting ogfile will make softlink unsuable
    • like Windows shortcut
  • hardlink
    • ln ogfile hardlink
    • create a pointer to the data ogfile points to
    • deleting ogfile won't affect hardlink

python

  • python -c <script>
  • pass things in with input()
    • echo 2 | python -c "print(int(input())+2)" → 4

calculate

  • bc
  • bc -l use some library
  • echo 2+2 | bc → 4