Notes from Learn with Mithiran: Introduction to Shell Scripting

Overview

• Topic: Introduction to Shell Scripting (Path 3 in Linux series)
• Previous topics: Linux fundamental commands and using regular expressions with grep and set commands.
• Future topics: Advanced concepts including looping and condition statements.

Setting Up Environment

• Installation on Windows:
  • Search and install Ubuntu from Microsoft Store.
  • Alternative: Create a Linux version on AWS EC2 (not demonstrated today).
• Windows Subsystem for Linux (WSL):
  • Check if WSL is enabled on the Windows machine.
  • Enable WSL by navigating to: Settings > Turn Windows features on or off > Check "Windows Subsystem for Linux".
  • Restart the system if required.

Installing Tools

1. Install Ubuntu:
   • Search Microsoft Store for Ubuntu and click on the 'Get' button.
2. Install Visual Studio Code (VS Code):
   • Search for VS Code in the browser and download it for Windows.
   • Install the WSL extension in VS Code.
3. Run VS Code:
   • Open VS Code from the Ubuntu terminal using the command code .

Basics of Shell Scripting

• What is Shell Scripting?:
  • A method to communicate with the computer using a programming language.
  • Shells: Bash (Born Again SHell), Z-Shell, K-Shell, etc.
• Interacting with Linux:
  • Use commands like pwd (print working directory) and ls (list files).
  • Shell scripts allow you to write commands in a file and execute them.

Writing a Shell Script

1. Creating a Shell Script:
   • Create a file named main.sh.
   • Start with a shebang #!/bin/bash to specify the shell.
   • Write commands (e.g., pwd, ls) in the file.
2. Running a Shell Script:
   • Make the script executable with chmod +x main.sh.
   • Run it using ./main.sh or sh main.sh.

Variables in Shell Scripting

• Defining Variables:
  • Syntax: variable_name=value (e.g., a=10).
  • Print variable value with echo $variable_name.
• Rules for Variables:
  • First character must be a letter or underscore.
  • Use uppercase for variable names as a convention.
• Types of Variables:
  • Local Variables: Defined within scripts.
  • Environment Variables: Accessible system-wide.
  • Shell Variables: System variables available to the shell.

Input and Output

• Using echo:
  • Display output in the terminal (e.g., echo Hello World).
• Using read:
  • Capture user input (e.g., read name).
  • Combine with echo to greet users (e.g., echo Hey nice to meet you, $name).

Special Variables

• Command-Line Arguments:
  • $0: Name of the script.
  • $1, $2: Arguments passed to the script.
  • $#: Number of arguments passed.
  • $$: Process ID of the current shell.
  • $?: Exit status of the last command.

Operators in Shell Scripting

1. Arithmetic Operators:
   • Use expr to evaluate expressions (e.g., expr $a + $b).
2. Relational Operators:
   • Compare values (e.g., -eq, -ne, -gt, -lt).
3. String Operators:
   • Check if strings are empty or equal (e.g., -z, -n).
4. File Operators:
   • Check if a file exists or is readable/writable (e.g., -e, -r, -w).

Conclusion

• Today's focus: Basics of setting up Linux, shell scripting fundamentals, variables, and operators.
• Future sessions will cover loops and conditionals.
• Encouragement to like and subscribe to the channel for more content.