Unix / Linux - Quick Guide

Welcome, aspiring programmers! As an experienced computer science teacher, I'm thrilled to guide you through the fascinating world of Unix and Linux. Don't worry if you're new to programming – we'll start from the basics and build our way up. Let's embark on this exciting journey together!

1. What is Unix?

Unix is an operating system that was developed in the 1960s and has since become the foundation for many modern operating systems, including Linux. It's known for its stability, flexibility, and powerful command-line interface.

1.1 Unix Architecture

Unix follows a layered architecture, consisting of:

1. The kernel (core of the system)
2. The shell (interface between user and kernel)
3. Utilities and applications

Think of Unix like a three-layer cake: the kernel is the base, the shell is the frosting, and the utilities are the delicious toppings!

2. Getting Started with Unix/Linux

2.1 The Command Line Interface (CLI)

Unix/Linux systems primarily use a command-line interface. Don't be intimidated – it's like learning a new language, and soon you'll be fluent!

To start, open your terminal. You'll see something like this:

username@hostname:~$

This is your command prompt, waiting for your instructions!

2.2 Basic Commands

Let's start with some simple commands:

Command	Description	Example
pwd	Print Working Directory	pwd
ls	List files and directories	ls
cd	Change Directory	cd Documents
mkdir	Make Directory	mkdir MyFolder
touch	Create an empty file	touch myfile.txt

Let's try them out!

$ pwd
/home/username

$ ls
Documents  Downloads  Music  Pictures

$ mkdir MyProject

$ cd MyProject

$ touch hello.txt

$ ls
hello.txt

Each command does a specific job. pwd shows where you are, ls lists what's around you, mkdir creates a new folder, cd moves you to a different location, and touch creates a new file.

3. File Management

3.1 Creating and Editing Files

Let's create a simple text file using the nano editor:

$ nano hello.txt

This opens the nano editor. Type some text:

Hello, Unix world!
This is my first file.

Press Ctrl+X, then Y, then Enter to save and exit.

3.2 Displaying File Content

To view the content of your file:

$ cat hello.txt
Hello, Unix world!
This is my first file.

The cat command displays the entire file content.

3.3 Copying, Moving, and Deleting Files

Here's a quick reference table:

Command	Description	Example
cp	Copy files or directories	cp hello.txt hello_copy.txt
mv	Move or rename files	mv hello.txt greetings.txt
rm	Remove files or directories	rm hello_copy.txt

Let's try these:

$ cp hello.txt hello_backup.txt
$ ls
hello.txt  hello_backup.txt

$ mv hello.txt greetings.txt
$ ls
greetings.txt  hello_backup.txt

$ rm hello_backup.txt
$ ls
greetings.txt

Remember, with great power comes great responsibility. Be careful with the rm command – there's no recycle bin in the command line!

4. Directory Management

4.1 Navigating Directories

We've already seen cd for changing directories. Here are some navigation tips:

• cd .. moves up one directory
• cd ~ takes you to your home directory
• cd / goes to the root directory

$ pwd
/home/username/MyProject

$ cd ..
$ pwd
/home/username

$ cd ~
$ pwd
/home/username

$ cd /
$ pwd
/

4.2 Creating and Removing Directories

We've seen mkdir for creating directories. To remove them, use rmdir:

$ mkdir TestDir
$ ls
TestDir  MyProject

$ rmdir TestDir
$ ls
MyProject

Note: rmdir only works on empty directories. For non-empty directories, you'd use rm -r, but be very careful with this!

5. File Permissions

Unix/Linux systems have a robust permissions system. Each file and directory has permissions for the owner, group, and others.

5.1 Understanding Permissions

Use ls -l to see detailed file information, including permissions:

$ ls -l
-rw-rw-r-- 1 username username 35 Jun 15 10:30 greetings.txt

The permissions are represented by -rw-rw-r--:

• The first character indicates the file type (- for regular file, d for directory)
• The next three characters are owner permissions
• The next three are group permissions
• The last three are permissions for others

Each set of three characters represents read (r), write (w), and execute (x) permissions.

5.2 Changing Permissions

Use the chmod command to change permissions:

$ chmod 644 greetings.txt
$ ls -l greetings.txt
-rw-r--r-- 1 username username 35 Jun 15 10:30 greetings.txt

Here, 644 is an octal representation:

• 6 (110 in binary) means read and write for the owner
• 4 (100 in binary) means read-only for group and others

Conclusion

Congratulations! You've taken your first steps into the world of Unix/Linux. We've covered the basics of navigating the file system, managing files and directories, and understanding permissions. Remember, practice makes perfect – the more you use these commands, the more comfortable you'll become.

In our next lessons, we'll dive deeper into more advanced topics like shell scripting, process management, and network utilities. Until then, keep exploring and don't be afraid to experiment in your Unix/Linux playground!

Credits: Image by storyset