Basics of shell scripting in centos

Shell scripting allows you to automate tasks and execute commands in a sequence, making it a powerful tool for system administration and automation on CentOS. Here are the basics of shell scripting:

1. Choose a Shell:

• CentOS uses the Bash shell (/bin/bash) by default, which is the most common shell on Unix-like systems.
• Other shells like Zsh, Ksh, and Dash are also available but less commonly used.

2. Create a Script File:

• Create a new file with a .sh extension (e.g., script.sh) to write your shell script.
• Use a text editor like nano, vim, or gedit to create and edit the script file.

3. Set the Shebang Line:

• Start the script with a shebang line (#!) followed by the path to the shell interpreter.
• For Bash scripts, use #!/bin/bash.

4. Write Shell Commands:

• Write shell commands in the script file to perform specific tasks or execute commands.
• Commands can include system commands, utilities, redirections, pipes, variables, loops, conditionals, functions, and more.

5. Execute the Script:

• Make the script executable using the chmod command:

  chmod +x script.sh 

• Run the script by typing its filename preceded by ./:

  ./script.sh 

6. Variables:

• Use variables to store data or values that can be reused throughout the script.
• Declare variables without spaces around the equals sign:

  variable_name=value 

• Access variables using the $ prefix:

  echo $variable_name 

7. Control Structures:

• Use control structures like loops and conditionals to control the flow of execution in the script.
• Example of a for loop:

  for i in {1..5} do echo "Number: $i" done 

8. Functions:

• Define functions to encapsulate code blocks that perform specific tasks.
• Example of a function:

  my_function() { echo "Hello, world!" } my_function 

9. Input and Output:

• Read input from users using the read command:

  echo "Enter your name:" read name echo "Hello, $name!" 

• Redirect output to files or pipes using redirection operators (>, >>, <, |, etc.).

10. Comments: - Use comments to add explanatory notes or annotations to your script for better readability. - Comments start with the # symbol and extend to the end of the line.

11. Error Handling: - Implement error handling mechanisms to handle errors gracefully and provide informative error messages to users. - Use exit to terminate the script with a specific exit code in case of errors.

12. Debugging: - Use debugging techniques like set -x to enable debugging mode and trace the execution of commands in the script. - Print debugging messages using the echo command to troubleshoot issues.