Shell scripting in Linux

1. Shebang: Specifies the interpreter to be used for executing the script.

    shellCopy code#!/bin/bash
   

2. Comments: Used for adding comments in the script to provide information or explanations.

    shellCopy code# This is a comment
   

3. Variables: Used to store values.

    shellCopy codevariable_name=value
   

4. Command substitution: Allows the output of a command to replace the command itself.

    shellCopy codevariable_name=$(command)
   

5. Conditionals: Used to perform actions based on certain conditions.

    shellCopy codeif condition
    then
        # commands
    elif condition
    then
        # commands
    else
        # commands
    fi
   

6. Loops: Used to iterate over a sequence of values or perform repetitive tasks.

   • For loop:

       shellCopy codefor variable in list
       do
           # commands
       done
     

   • While loop:

       shellCopy codewhile condition
       do
           # commands
       done
     

   • Until loop:

       shellCopy codeuntil condition
       do
           # commands
       done
     

7. Functions: Used to group a set of commands into a reusable block.

    shellCopy codefunction_name() {
        # commands
    }
   

8. Input/output redirection:

   • Redirecting standard output (stdout) to a file:

       shellCopy codecommand > file
     

   • Redirecting standard error (stderr) to a file:

       shellCopy codecommand 2> file
     

   • Appending stdout to a file:

       shellCopy codecommand >> file
     

   • Redirecting stderr and stdout to different files:

       shellCopy codecommand > stdout_file 2> stderr_file
     

9. Command-line arguments: Allowing passing arguments to a script.

    shellCopy codescript_name arg1 arg2 arg3
   

10. Conditional execution:

    • Execute a command only if the previous command succeeds (return code 0):

        shellCopy codecommand1 && command2
      

    • Execute a command only if the previous command fails (return code non-zero):

        shellCopy codecommand1 || command2
      

11. Exit status: Checking the exit status of a command.

    shellCopy code$?
    

12. String manipulation:

    • Concatenating strings:

        shellCopy codenew_string="$string1$string2"
      

    • Extracting substrings:

        shellCopy codesub_string="${string: start: length}"
      

    • String length:

        shellCopy codelength=${#string}
      

These are just a few essential commands and concepts in shell scripting. The possibilities and complexities of shell scripting are vast, and there are many more commands and features available.