list of helpful bash commands

command_list

Legend

|    symbol   |      used for       |
|=============|=====================|
|      -      | command description |
|      #      | comments            |
|      $      | actual command      |
|      []     | command's output    |
|      <>     | command's arguments |

|========================================================================================================================|

- display git branch inside terminal by configuring .bashrc file
  parse_git_branch() {
     git branch 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/ [ \1]/'
  }
  export PS1="\[\033[32m\]\w\[\033[33m\]\$(parse_git_branch)\[\033[00m\] λ " 

- run previously executed command using double bangs (!!)
  $ date [Wed Nov 27 21:11:03 PKT 2019]
  $ !! [Wed Nov 27 21:11:03 PKT 2019]

- go back to root directory using tilda (~)
  $ cd ~ [/home/tam101]

- go back to previous directory using hyphen (-)
  $ cd - 

- check differences between contents of 2 files using diff side by side. 
    Assume file text_1 containing "hello world" as text and text_2 
    contatining "hello" only. use --color flag to highlight the text.
  $ diff text_1 text_2 --side-by-side [hello world |	hello]

- use double dots (..) to go back to immediate parent directory
  $ cd ../

- display calender on ternimal using cal
  $ cal <year>

- create multiple files using {..} operator
  $ touch text_{1..3} # creates files with names text_1, text_2 & text_3

- check the port # which is currently being used in 2 ways
  1. using netstat
    # netstart -pant | grep ":<port #>"
    $ sudo netstat -pant | grep ":8080" [tcp 0  0 0.0.0.0:8080  0.0.0.0:* LISTEN 28967/node]
  2. using lsof
    # lsof -i | grep <command/process name>
    $ lsof -i | grep firefox [firefox 27535 in01-nbk-567 346u IPv4 545324  0t0  TCP in01nbk567-Latitude-5591:33784->52.114.77.38:https (ESTABLISHED)]

- kill a process which is binded to a particular port number
  # lsof -i:<port number>
  $ lsof -i:8080

- adjusting brightness of external monitor using xrandr
  # xrandr --output <port name)> --brightness <0.0 - 1.0>
  $ xrandr --output HDMI1 --brightness 0.6

- check path of specific python's installation 
  $ which python3 [/usr/bin/python3] 

- creating python virtual-environment with specific python verion
  # virtualenv --python=<path/to/python/installation/folder> <path/to/new/virtualenv/>
  $ virtualenv --python=/usr/bin/python3.6 code_repository
 
- using new SSH key pair instead of HTTP for Github repository authentication
  1. create new SSH private-public key pair. replace dummy email id with the one used in Github account
    $ ssh-keygen -t rsa -b 4096 -C "[email protected]"
  2. next, press Enter for default location (/home/you/.ssh/id_rsa) for saving the keys
  3. next, enter passphrase for the SSH key (empty for no passphrase). re-confirm it by enterting it again.
  4. now add the private key to SSH agent
    $ eval "$(ssh-agent -s)" # starts the SSH agent
    $ ssh-add ~/.ssh/id_rsa
  5. finally, add the public SSH key to the Github account
    a. install xclip utility 1st in bash
      $ sudo apt install xclip
    b. copy the contents of key using xclip
      $ xclip -sel clip < ~/.ssh/id_rsa.pub
    c. got to github account settings and click on "SSH and GPG key" sidebar
    d. click on "new SSH key", give key a meaningful name and paste the contents in the box.

- setting up postgres in ubuntu/linux-mint
  1. update the repository list
    $ sudo apt-get update
  2. install postgres & postgres-contrib
    $ sudo apt install postgresql postgresql-contrib
 
 - unblock bluetooth device using rfkill
   $ rfkill list 
   # rfkill unblock <ID>
   $ rfkill unblock 1
  
 - custom aliases
  alias install="sudo apt-get install "
  alias update="sudo apt-get update "
  alias upgrade="sudo apt-get upgrade "
  alias automremove="sudo apt-get autoremove "
  alias purge="sudo apt-get purge"
  alias snit="sudo snap install "
  alias snrp="sudo snap remove "
  alias kt="microk8s kubectl "
  alias sbr1="xrandr --output HDMI-1 --brightness "