Scripting Classroomnotes 02/Feb/2023

User Shell

Setting up the user shell

• PS1
  • In the home directory we have file called as .bashrc
  • .bashrc is a configuration file in Linux that contains commands and setings specific to the bash shell. This is executed every time a new bash shell is launched.
  • This can be used to set environmental variables, aliases and other shell customizations
  • backup the existing bashrc file cp ~/.bashrc ~/bashrc.tmp
  • open the bashrc and find PS1
    
  • Lets change this to PS1="QTDevOpsPrompt> "
    
  • Lets change PS1 PS1="\u@\H> \A "
    
  • Refer Here for the PS1 possibilities
  • Shell variable PS1 can be used to customize look and feel of our shell.
  • PS1 is called as primary prompt display variable
• Alias
  • Lets add the following statements in the bash rc file
    alias proc="ps auwwx"
alias pfilter="ps auwwx | grep"
alias start="systemctl start "
alias stop="systemctl stop "
alias enable="systemctl enable "
  • proc = list of all processes
  • to filter the process according to keyword
    
  • Now apply and execute
    
• Adjust the Bash history
  • In the bash rc file as shown in the highlighted section below
    
  • Bash shell remembers 1000 typed commands in history in the current session and to save more than 2000 commands in the history file called .bash_history
• Adjust the PATH variable
  • We can edit the ~/.profile and PATH for the current user
    
• SPECIAL VARIABLES in bashrc
  • PS1, PS2, PS3 and PS4
  • HISTSIZE, HISTFILESIZE
  • OLDPWD
  • PWD
• Refer Here for all the variables and Refer Here for Shell initialization files

Writing our first shell script

• Lets write a script which prints Hello, Shell Scripting
  
• add execute permissions sudo chmod +x <filename>.sh
• cheatsheet Refer Here
• Refer Here for official docs
• Refer Here for how to get a shell script to actually work.

Note

• Lab Environment:
  • ubuntu 20.04
  • centos 8