1. Intro to Bash

Description: Bash (Bourne Again SHell) is a command-line interface and scripting language used in Unix-like operating systems, such as Linux and macOS. It allows users to interact with the system, run programs, and automate tasks.
Example:
```
echo "Hello, World!"
```
This command prints "Hello, World!" to the terminal.

How to Access Bash Shell from Different Operating Systems:

a. Linux:

Default: On most Linux distributions, Bash is the default shell. You can open it using:
- Terminal: Search for "Terminal" in the applications menu or press Ctrl + Alt + T.
- Once the terminal opens, you will be in Bash by default.

b. macOS:

Default: In older versions of macOS, Bash was the default shell. In newer versions (from Catalina onward), it was replaced by Zsh, but Bash is still available.
- Terminal: Search for "Terminal" using Spotlight (Cmd + Space, then type "Terminal" and press Enter).
- Once the terminal opens, you can start a Bash session by typing:
```
bash
```

c. Windows:

Windows 10 and Windows 11:
- Windows Subsystem for Linux (WSL): If you have WSL installed, you can access Bash by:
  - Searching for "Ubuntu" or any other Linux distribution you installed from the Start menu, or typing "bash" in the Command Prompt (cmd).
  - Once opened, a terminal window with Bash will be ready to use.
- Git Bash: Another alternative is using Git Bash, which comes with Git for Windows.
  - Download and install Git for Windows.
  - After installation, search for "Git Bash" in the Start menu.
PowerShell or Command Prompt: You can install Bash through WSL:
- Open PowerShell as an administrator (Run as administrator).
- Run the following command to install Ubuntu:
```
wsl --install
```
- After installation and a restart, you can search for "Ubuntu" and open it from the Start menu.

2. Basic Bash Commands

Description: Bash provides basic commands to navigate the filesystem and manage files.

Examples:

 # List directory contents

 ls        # Lists files and directories in the current directory
 ls -l     # Lists in long format with detailed information
 ls -a     # Lists all files, including hidden files

 # Change directory

 cd /path/to/directory  # Changes the current directory
 cd ..     # Moves up one directory level
 cd ~      # Changes to the home directory
 
 # Print Working Directory

 pwd       # Prints the full path of the current directory
 
 # Create, Move, and Delete Files/Directories

 touch filename.txt  # Creates an empty file named filename.txt
 mkdir my_directory  # Creates a new directory named my_directory
 mv filename.txt /path/to/destination/  # Moves or renames a file
 cp filename.txt /path/to/destination/  # Copies a file
 rm filename.txt    # Deletes a file
 rm -r my_directory # Deletes a directory and its contents
 
 # Display File Content

 cat filename.txt   # Displays the content of a file
 less filename.txt  # Displays the content of a file one page at a time
 head filename.txt  # Shows the first 10 lines of a file
 tail filename.txt  # Shows the last 10 lines of a file
 
 # Search and Find

 grep "pattern" filename.txt  # Searches for a pattern in a file
 find /path/to/search -name "filename"  # Finds files in a directory hierarchy
 
 # Permissions

 chmod 755 filename.txt  # Changes file permissions

3. Manipulate Files using Wildcards

Description: Wildcards are special characters that allow you to specify patterns to match filenames. They are useful for manipulating multiple files at once.
Wildcards:
- *: Matches any number of characters, including none.
- ?: Matches exactly one character.
- []: Matches any one of the enclosed characters.
- [!char] or [^char]: Matches any character not enclosed in the brackets.

Examples:

# Using the '*' wildcard
ls *.txt       # Lists all files ending with .txt
rm file*       # Deletes all files starting with 'file'
mv *.jpg /images/  # Moves all .jpg files to the images directory

# Using the '?' wildcard
ls ?.txt       # Lists files with a single character name followed by .txt (e.g., a.txt, b.txt)
cp file?.txt /backup/  # Copies files named 'file1.txt', 'file2.txt', etc., to the backup directory

# Using '[]' wildcard
ls file[123].txt   # Lists files named file1.txt, file2.txt, and file3.txt
mv report[0-9].pdf /reports/  # Moves report0.pdf, report1.pdf, ..., report9.pdf to the reports directory

# Using '[!char]' or '[^char]' wildcard
ls [!abc]*.txt   # Lists all .txt files not starting with 'a', 'b', or 'c'
rm [^0-9]*.log   # Deletes all .log files not starting with a digit

# Combining wildcards
ls *.t?          # Lists files with extensions like .txt, .tar, etc.
mv file[1-5]?.* /destination/  # Moves files like file1a.txt, file2b.pdf, file3c.doc, etc.

4. Pipelines

Description: Pipelines use the | character to pass the output of one command as the input to another.
Example:
```
ls -l | grep ".txt"  # Lists all .txt files with detailed information
```
Here, ls -l lists files in detail, and grep ".txt" filters the results to show only .txt files.

5. Background Jobs

Description: Run processes in the background so the terminal remains available for other commands.
Examples:
```
long_running_command &
```
The & at the end runs the command in the background.

6. Aliases

Description: Aliases are shortcuts for longer commands.

Examples:

alias ll='ls -la'  # Creates an alias 'll' for 'ls -la'
alias rm='rm -i'   # Prompts before deleting files

Use unalias to remove an alias:

unalias ll

7. Bash Variables

Create Shell Variables:
- Description: Store data for later use.
- Example:
```
greeting="Hello, World!"
echo $greeting
```
Variables Quoting and Backslash Escaping:
- Description: Use quotes to handle spaces or special characters in variables.
- Examples:
```
message="This is a message with spaces"
echo "$message"

special_chars="Special\$Char!"
echo "$special_chars"
```

Built-In Variables:

Description: Bash has several built-in variables like $HOME (user's home directory) and $PWD (current directory).

Example:

echo $HOME  # Prints the home directory
echo $PWD   # Prints the current directory
printenv    # Prints all the environment variables

8. Special Files

Concept of Special Files:
- Description: Special files, like .bashrc, configure the shell environment.

Creating .bashrc:

Example:

echo 'alias ll="ls -la"' >> ~/.bashrc  # Adds an alias to .bashrc
source ~/.bashrc                       # Applies changes

9. Bash Script File Format

Description: Bash scripts are text files containing a series of commands. They start with a "shebang" (#!) line.

Example:

#!/bin/bash
echo "This is a Bash script."

10. Run Script

Description: To run a Bash script, make it executable and run it.

Example:

chmod +x script.sh  # Makes the script executable
./script.sh         # Runs the script

11. PATH Variable

View PATH Variable’s Value:
- Description: The PATH variable lists directories where the system looks for executable files.
- Example:
```
echo $PATH
```

Changing PATH Value and Run Script:

Example:

export PATH=$PATH:/path/to/directory  # Temporarily adds a directory to PATH

12. Positional Parameters

Description: Positional parameters in Bash are used to pass arguments to a script or function. $1, $2, etc., represent the first, second, and subsequent arguments passed to the script. $0 represents the script's name, and $@ or $* represents all the arguments.

Example:

#!/bin/bash

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "All arguments: $@"

# Run this script with: ./script.sh arg1 arg2

This script prints the script's name and the arguments passed to it when executed.

13. Functions within Bash Script

Description: Functions are reusable blocks of code.

Example:

function greet() {
  echo "Hello, $1"
}
greet "Alice"  # Outputs: Hello, Alice

14. Bash Conditions

Description: Use if, then, else, and fi for conditional statements.

Example:

if [ -f "file.txt" ]; then
  echo "File exists."
else
  echo "File does not exist."
fi

15. Bash Loop

Description: Loops iterate over a series of items.

Examples:

# For loop
for i in 1 2 3; do
  echo "Number: $i"
done

# While loop
count=1
while [ $count -le 3 ]; do
  echo "Count: $count"
  ((count++))
done

16. Bash Case

Description: case statements handle multiple conditions.

Example:

case "$1" in
  start)
    echo "Starting..."
    ;;
  stop)
    echo "Stopping..."
    ;;
  *)
    echo "Usage: $0 {start|stop}"
    ;;
esac

This script takes a command-line argument and matches it to start or stop. If neither matches, it shows a usage message.

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bash-scripting.md

bash-scripting.md

1. Intro to Bash

How to Access Bash Shell from Different Operating Systems:

a. Linux:

b. macOS:

c. Windows:

2. Basic Bash Commands

3. Manipulate Files using Wildcards

4. Pipelines

5. Background Jobs

6. Aliases

7. Bash Variables

8. Special Files

9. Bash Script File Format

10. Run Script

11. PATH Variable

12. Positional Parameters

13. Functions within Bash Script

14. Bash Conditions

15. Bash Loop

16. Bash Case

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1. Intro to Bash

How to Access Bash Shell from Different Operating Systems:

a. Linux:

b. macOS:

c. Windows:

2. Basic Bash Commands

3. Manipulate Files using Wildcards

4. Pipelines

5. Background Jobs

6. Aliases

7. Bash Variables

8. Special Files

9. Bash Script File Format

10. Run Script

11. PATH Variable

12. Positional Parameters

13. Functions within Bash Script

14. Bash Conditions

15. Bash Loop

16. Bash Case