01-Scripting-Basics

Shell Scripting Basics

Task 1: First Script

1. Create a file hello.sh
2. Add the shebang line #!/bin/bash at the top
3. Print Hello, DevOps! using echo
4. Make it executable and run it

Script

• What happens if you remove the shebang line?

• The script runs after removing shebang line :
  • ./hello.sh - The kernel checks for a shebang to identify the interpreter.If no shebang is found, the script is executed using the current shell.
  • bash hello.sh - The script is explicitly executed by the Bash shell,independent of the presence of a shebang.
  • sh hello.sh - The script is executed using the sh shell,which may differ in behavior from bash

---

Task 2: Variables

1. Create variables.sh with:
   • A variable for your NAME
   • A variable for your ROLE (e.g., "DevOps Engineer")
   • Print: Hello, I am <NAME> and I am a <ROLE>
2. Try using single quotes vs double quotes — what's the difference?

• Using double quote " " - Allow variable expansion
• Using single quote ' ' - Treat every character exactly as written

Script

---

Task 3: User Input with read

1. Create greet.sh that:
   • Asks the user for their name using read
   • Asks for their favourite tool
   • Prints: Hello <name>, your favourite tool is <tool>

Script

---

Task 4: If-Else Conditions

1. Create check_number.sh that:
   • Takes a number using read
   • Prints whether it is positive, negative, or zero

Script

2. Create file_check.sh that:
   • Asks for a filename
   • Checks if the file exists using -f
   • Prints appropriate message

Script

---

Task 5: Combine It All

Create server_check.sh that:

1. Stores a service name in a variable (e.g., nginx, sshd)
2. Asks the user: "Do you want to check the status? (y/n)"
3. If y — runs systemctl status <service> and prints whether it's active or not
4. If n — prints "Skipped."

Script

What I learned -

• How to write and execute Bash shell scripts using the shebang (#!/bin/bash),variables,and user input with read.
• How variable assignment works in Bash,including accessing variables with $ and understanding single vs double quotes.
• How to control script flow using conditional statements (if, elif, else) and test operators (-f, -gt, -lt).
• How to check file existence and numeric conditions inside shell scripts.
• How to suppress command output using redirection (> /dev/null ).
• How to use systemctl is-active to programmatically check whether a service is running instead of relying on verbose status output.