# Fundamentals of Bash

***

## **Bash Scripting Basics Guide**

#### **1. Introduction to Shell and Bash**

A **shell** is an interface that allows users to interact with the operating system. It interprets the commands you enter and executes them.

* **Bash (Bourne Again Shell)** is the most commonly used shell on Linux systems and is widely used for scripting, automating tasks, and managing system processes.
* Bash is a **command processor** that typically runs in a text window where users type commands that cause actions. It's the default shell on most Linux distributions.

#### **2. Other Common Shells**

There are multiple types of shells in Linux, and here are a few common ones:

* **Bash** (`/bin/bash`): Default shell for many Linux distributions.
* **Zsh** (`/bin/zsh`): An extended version of Bash, with more features.
* **Ksh** (`/bin/ksh`): Korn shell, known for its advanced scripting capabilities.
* **Fish** (`/usr/bin/fish`): A user-friendly shell with a focus on interactive features.

#### **3. Checking and Changing the Current Shell**

To see which shell you're currently using:

```bash
echo $SHELL
```

To change your shell temporarily:

```bash
bash     # or zsh, ksh, etc.
```

To permanently change the default shell, you can use:

```bash
chsh -s /bin/zsh
```

This command changes your default shell, but requires you to log out and log back in for the changes to take effect.

***

### **4. Basic Syntax of Bash Scripts**

Before diving into an exercise, let’s quickly cover some of the essential components of a Bash script:

* **Shebang (`#!`)**: Tells the system what interpreter to use to execute the script. Most scripts will use `#!/bin/bash`.
* **Variables**: Used to store and manipulate data.
* **Conditionals**: `if`, `else`, `elif` used for decision-making.
* **Loops**: `for`, `while`, and `until` used to repeat actions.
* **Input/Output Redirection**: Redirecting input/output with operators (`>`, `>>`, `|`).

#### **Basic Script Structure**

```bash
#!/bin/bash
# This is a comment
# Script code goes here
```

***

### **5. Sample Script: System Information and Monitoring Tool**

#### **Exercise Objective**:

This script will:

1. Create a directory.
2. Move a file into the directory.
3. Copy the file back out of the directory.
4. Display the file listing at each step.
5. Remove the directory and file (as a cleanup step).

<https://github.com/bc0de0/bash-scripts/blob/master/bash_basics.sh>

***

#### **6. How to Run the Script:**

1. Open a terminal and create a new script file:

   ```bash
   nano bash_basics.sh
   ```
2. Paste the sample script into the file and save it.
3. Make the script executable:

   ```bash
   chmod +x bash_basics.sh
   ```
4. Run the script:

   ```bash
   ./bash_basics.sh
   ```