Bourne Again Shell (bash)

History

The Bourne Again Shell (Bash) is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne Shell (sh). First released in 1989, Bash has become the default shell on many Linux distributions and macOS.

Features

Command History: Allows users to recall and edit previous commands.
Tab Completion: Automatically completes file names and commands.
Scripting: Supports writing scripts to automate tasks.
Job Control: Manages multiple processes within a single shell session.
Aliases: Creates shortcuts for frequently used commands.

Basic Commands

pwd: Print the current working directory.
cd [directory]: Change the current directory to the specified directory.
ls: List the contents of the current directory.

File and Directory Management

touch [filename]: Create a new empty file.
mkdir [directory]: Create a new directory.
rm [filename]: Remove a file.
rmdir [directory]: Remove an empty directory.
cp [source] [destination]: Copy a file or directory.
mv [source] [destination]: Move or rename a file or directory.

Scripting

Basic Script

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

Variables

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

Conditional Statements

#!/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

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

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

greet "Alice"
greet "Bob"

File Operations

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

#!/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

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