Scripts

Shell scripting involves writing a series of commands for the shell to execute. Shell scripts can automate repetitive tasks, manage system operations, and perform complex operations by combining multiple commands.

Basic Shell Script Example

Here is a simple example of a shell script that prints "Hello, World!" to the terminal:

#!/bin/bash
# This is a comment
echo "Hello, World!"

Variables

Variables in shell scripts are used to store data that can be referenced and manipulated throughout the script.

#!/bin/bash
name="John"
echo "Hello, $name!"

Conditional Statements

Conditional statements allow the script to make decisions based on certain conditions.

#!/bin/bash
number=10
if [ $number -gt 5 ]; then
  echo "The number is greater than 5"
else
  echo "The number is 5 or less"
fi

Loops

Loops are used to repeat a set of commands multiple times.

For Loop

#!/bin/bash
for i in {1..5}; do
  echo "Iteration $i"
done

While Loop

#!/bin/bash
counter=1
while [ $counter -le 5 ]; do
  echo "Counter: $counter"
  ((counter++))
done

Functions

Functions in shell scripts allow you to group commands into reusable blocks.

#!/bin/bash
greet() {
  echo "Hello, $1!"
}

greet "Alice"
greet "Bob"

File Operations

Shell scripts can perform various file operations such as creating, reading, and deleting files.

Creating a File

#!/bin/bash
echo "This is a new file" > newfile.txt

Reading a File

#!/bin/bash
while IFS= read -r line; do
  echo "$line"
done < newfile.txt

Deleting a File

#!/bin/bash
rm newfile.txt

Example: Backup Script

Here is an example of a shell script that creates a backup of a directory:

#!/bin/bash
source_dir="/path/to/source"
backup_dir="/path/to/backup"
timestamp=$(date +%Y%m%d%H%M%S)
backup_file="$backup_dir/backup_$timestamp.tar.gz"

tar -czf $backup_file $source_dir
echo "Backup created at $backup_file"

This script compresses the contents of the source directory into a tar.gz file and saves it in the backup directory with a timestamp.

Last modified: 14 December 2024