Scripting Classroomnotes 29/Oct/2022

Scripting

• Any scripting is sequence of instructions.
• In Linux instruction is a command & in Powershell the instruction is also command but called as Cmd-Let
• Scripts are created for two possible ways of execution
  • interactive scripts:
    • to simplify the execution of complex problems/installations/configurations
  • non-interactive scripts:
    • to automate certain activity.
• Lets try to setup dev environment for shell and powershell scripts.

Developer Environment

• Windows
  • Ensure Visual studio code is installed
  • Ensure Git Bash is installed
• Mac:
  • Ensure Visual Studio code is installed.
• Shell script has an extension of .sh
• Powershell scripts have an extension of .ps1
• Ensure Powershell extension is installed.
  
• Ensure bashdebug is installed
  
• To run the scripts:
  • ps1: run them from powershell
    • cd in to the folder
    • execute .\<filename>.ps1
  • sh: run the gitbash or mac terminal
    • cd in to the folder
    • execute bash ./<filename>.sh

Debugging

• IDE based Debugging:
  • Breakpoint: The line or instruction where the control is handed over to us.
  • Step Over: Execute the current instruction or line.
  • Powershell: Debugging is possible by installing Powershell extension
  • Shell Scripting: We need to do little more work to get the things in place.

Exit Codes in Linux

• Every Linux command returns a code
  • Zero: Command exectuion is success
  • Non-Zero: Command execution is failed
• To find the last return code use the following expression $?
• Refer Here for the bash cheatsheet.

Combining multiple Linux commands in one line

• Commands can be combined by using semi-colon ; and ampersand &&
  • ;: All the commands will be executed irrespective of errors
    
  • &&: All the commands will be executed if there are no errors. From the moment a command returns an error code the subsequent commands will not be executed
    

Note

• PS script

echo hello
echo 1
echo 2

• shell script

echo hello
echo 1
echo 2

• python script

def printargs(a,b):
    print(f"values passed are {a}, {b}")

def add(a, b):
    printargs(a,b)
    return a+b


if __name__ == '__main__':
    result = add(3, 5)
    print(result)
    result = add(5, 8)
    print(result)