Linux Classroom Series – 13/Aug/2020

Tools we will be using to write bash scripts

• Visual Studio Code
• Git Bash (Windows) / Terminal (Other Systems)
• RedHat Family & Ubuntu
• How to install Refer Here
• Creating Virtual Machines Refer Here for AWS Azure

Hello World

• Lets create a new file called as helloworld.sh and inside this

#!/bin/bash

echo "Hello World!"

• Now lets execute the script using bash helloworld.sh
• Generally all the shell scripts will have extensions of .sh
• What is #!/bin/bash?
  • It is called the shebang
  • It tells the linux system which binary to use to execute the script
  • For example if you were writing python code the shebang might be #!/usr/bin/python3
  • Since we are executing the shell scripts on bash prompt our shebang is #!/bin/bash
• To execute the program we have used bash command. If i have a shebang which already tells where the executable is still why do i need bash?
• Remember file permissions in linux (RWX) to execute scripts we need execute permissions, so lets check whats the permission which we have
• Now lets add execute permissions and run the script

Readability

• When writing scripts, aim to make sure the code is as readable as possible.

• How to make scripts readable?

  • Comments
  • Verbosity

• Comments:

  • Comments is nothing more than bit of text explaining what you are doing.
  • In shell the character which we use to denote comments is #
  • So lets add comments
  • Approach 1:

  #!/bin/bash
  
  # Print the text to the terminal
  echo "Hello World!"
  
  

  • Approach 2:

  #!/bin/bash
  
  echo "Hello World!" # Print the text to the terminal
  

  • Its often a good practice to have script header with fields like
    • Author
    • Version
    • Date
    • Description
    • Usage
  • Script headers and Comments make your scripts more professional

• Verbosity:

  • Verbosity is the balancing act between not too much but also not less explanation.
  • Lets discuss three types of verbosity
    • Verbosity in Comments:
      • Ensure your comments are punctual and smaller.
    • Verbosity in Commands:
      • Try to use long variant in commands as shown in the below example with ls -R & ls --recursive. Both give same results but long variant is readable
    • Verbosity in Command Outputs:
      • Always try to build scripts which take two argument -v/–verbose and -q/–quiet. When user runs your script with verbose parameter give detailed information about what is happening & in other case don’t display anything or display only absolutely required stuff to the terminal.

• Shell script is a sequence of linux commands that are to be executed in an order.