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Shell Scripting Basics

A shell script is an automation tool that bundles multiple commands into a single file for execution.

1. Getting Started with Shell Scripts​

On the first line of your file, include a Shebang to specify that the file is a shell script.

#!/bin/bash

echo "Hello, Linux!"

How to run:

chmod +x hello.sh  # Grant execution permission
./hello.sh         # Run from the current directory

2. Defining and Using Variables​

  • Ensure there are no spaces around the = sign during declaration.
  • Use the $ symbol when referencing the variable.
NAME="Linux"
echo "Welcome to $NAME"

3. Conditional Statements (if)​

Conditions are written inside square brackets [ ]. Pay close attention to the spaces within the brackets.

FILE="data.log"

if [ -f "$FILE" ]; then
    echo "The file exists."
else
    echo "The file does not exist."
fi

4. Loops (for / while)​

# Iterating from 1 to 5
for i in {1..5}; do
    echo "Number: $i"
done

5. Practical Example: Backup Script​

#!/bin/bash
DATE=$(date +%Y%m%d)
BACKUP_DIR="/backup/$DATE"

mkdir -p $BACKUP_DIR
cp -r /var/www/html $BACKUP_DIR

echo "Backup complete: $BACKUP_DIR"

Mastering shell scripting allows you to automate a large portion of server operations. Great job!

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