Day 2: Basic Command Line Operations

Objectives

• Learn basic command line operations.
• Understand file and directory management.
• Get familiar with permissions and how to modify them.

---

1. Basic Command Line Operations

Navigating the File System

1. Print Working Directory

   • Display the current directory:

     $ pwd

2. Listing Directory Contents

   • List files and directories in the current directory:

     $ ls

   • List detailed information including hidden files:

     $ ls -al

3. Changing Directories

   • Change to a specific directory:

     $ cd /path/to/directory

   • Change to the home directory:

     $ cd ~

   • Change to the previous directory:

     $ cd -

File and Directory Management

1. Creating Directories

   • Create a new directory:

     $ mkdir new_directory

2. Creating Files

   • Create an empty file:

     $ touch new_file

3. Copying Files and Directories

   • Copy a file:

     $ cp source_file destination_file

   • Copy a directory and its contents:

     $ cp -r source_directory destination_directory

4. Moving/Renaming Files and Directories

   • Move or rename a file or directory:

     $ mv source destination

5. Deleting Files and Directories

   • Delete a file:

     $ rm file_name

   • Delete a directory and its contents:

     $ rm -r directory_name

---

2. Understanding Permissions

File Permissions Basics

• Each file and directory has permissions that control who can read, write, or execute them.
• Permissions are divided into three groups:
  • Owner: The user who owns the file.
  • Group: Users who are members of the file’s group.
  • Others: All other users.

Viewing Permissions

• Use the ls -l command to view detailed information, including permissions:

  $ ls -l

Permission Symbols

• Permissions are represented by a string of characters, e.g., -rwxr-xr--.
  • -: File type (e.g., - for a regular file, d for a directory).
  • r: Read permission.
  • w: Write permission.
  • x: Execute permission.
  • The first set of three characters represents the owner's permissions, the second set represents the group's permissions, and the third set represents others' permissions.

Changing Permissions

• Use the chmod command to change permissions.
  • Add permission:

    $ chmod +x file_name

  • Remove permission:

    $ chmod -w file_name

  • Set specific permissions (e.g., rwxr-xr--):

    $ chmod 754 file_name

Changing Ownership

• Use the chown command to change the owner of a file or directory:

  $ sudo chown new_owner file_name

• Change the group of a file or directory:

  $ sudo chown :new_group file_name

Using sudo for Superuser Privileges

• sudo allows a permitted user to execute a command as the superuser or another user.
  • Run a command with superuser privileges:

    $ sudo command

  • Example: Update package lists:

    $ sudo apt update

---

Practical Exercises

Exercise 1: Basic Navigation and Management

1. Open the terminal.
2. Navigate to the home directory:

   $ cd ~

3. Create a new directory named practice:

   $ mkdir practice

4. Navigate to the practice directory:

   $ cd practice

5. Create an empty file named example.txt:

   $ touch example.txt

6. List the contents of the directory:

   $ ls

Exercise 2: File Permissions

1. View the permissions of example.txt:

   $ ls -l example.txt

2. Add execute permission to the owner:

   $ chmod u+x example.txt

3. Verify the changes:

   $ ls -l example.txt

4. Remove write permission from others:

   $ chmod o-w example.txt

5. Verify the changes:

   $ ls -l example.txt

Exercise 3: Superuser Commands

1. Update the package list using sudo:

   $ sudo apt update

2. Install a package (e.g., curl):

   $ sudo apt install curl