Terminal Fundamentals

Once you open a terminal, you'll see a "shell prompt." This is where you type your commands. A typical prompt looks something like: username@hostname:current_directory$

Components:

• username: Your current Linux username.
• @: A separator.
• hostname: The name of your computer.
• :: Another separator.
• current_directory: Your current location. ~ (tilde) represents your home directory.
• $ or #: $ indicates a regular user, while # indicates the "root" user (superuser) with full system privileges. Be extra careful with a # prompt.

The prompt tells you who you are, where you are, and that the system is ready for your command.

Action: Shows the full path of the directory you are currently in.

Why: To know your exact location within the filesystem.

Example:

pwd

Output might be: /home/yourusername/Documents

Action: Allows you to move to a different directory.

Usage:

• Absolute Paths: Full path from root (e.g., cd /var/log).
• Relative Paths: Path relative to current directory (e.g., cd Documents, cd .. for parent, cd ../../ for two levels up).
• Shortcuts:
  • cd ~ or just cd: Navigates to your home directory.
  • cd -: Navigates to the previous directory you were in.

Example:

cd /home/user/Pictures
cd Projects
cd ..

Action: Lists files and directories within the current directory or a specified directory.

Common Options:

• ls: Basic listing.
• ls -l: Long format (permissions, owner, size, date).
• ls -a: Shows all files, including hidden files (starting with .).
• ls -la or ls -al: Combines long format with showing all files.
• ls -h: With -l, shows sizes in human-readable format (e.g., KB, MB).

Example:

ls
ls -l
ls -a Documents/
ls -lh /var/log

Action: Creates one or more new directories.

Common Options:

• mkdir -p ParentDir/ChildDir: Creates parent directories if they don't exist.

Example:

mkdir MyNewProject
mkdir -p ~/Projects/Archive/OldStuff

Action: Deletes an *empty* directory. If the directory contains files or other directories, rmdir will fail.

Why: For safely removing empty directories.

Example:

rmdir EmptyFolder

Action: Creates a new empty file if it doesn't exist. If the file already exists, touch updates its access and modification timestamps to the current time without changing its content.

Why: Quick way to create files or update modification times.

Example:

touch my_notes.txt
touch existing_file.log

Action: Copies files or directories.

Common Options:

• cp -r SourceFolder DestinationFolder: Copies a directory and its contents recursively.
• cp -i: Interactive mode, prompts before overwriting.
• cp -v: Verbose, shows what is being done.

Example:

cp file1.txt file1_backup.txt
cp report.doc Documents/
cp -r ~/MyProject /media/backup_drive/

Action: Moves files or directories from a source to a destination. It's also used to rename files or directories if the source and destination are in the same directory.

Example:

mv old_name.txt new_name.txt  # Rename
mv important_file.dat ~/SecureBackup/
mv ProjectX ~/Archive/OldProjects/

Action: Deletes files or directories. **This command is permanent; deleted items do not go to a "Trash Can" by default.**

Common Options:

• rm -i <file_name>: Interactive, prompts before each deletion.
• rm -r <directory_name>: Recursively removes a directory and all its contents.
• rm -f <item_name>: Force removal, suppresses prompts and ignores non-existent files.
• rm -rf <directory_name>: Force recursive removal. **EXTREMELY DANGEROUS if misused.** Double-check paths.

Example:

rm old_log.txt
rm -i sensitive_document.pdf
rm -r UnwantedFolder/

Warning: Be extremely careful with rm -rf, especially when combined with sudo or wildcards (*).

Action: Displays the manual page ("man page") for a command, providing comprehensive information about its syntax, options, and usage.

Navigating man pages: Use Arrow keys, Page Up/Down, or Spacebar to scroll. Type /search_term then Enter to search. Press q to quit.

Example:

man ls
man cp

Action: Many commands provide a shorter, summary help message directly to the terminal when used with the --help or sometimes -h option.

Why: Often quicker for a simple option reminder than reading the full man page.

Example:

mkdir --help
cp --help

What is sudo? sudo (Superuser Do) allows a permitted user to execute a command as another user, by default the "root" user (system administrator), who has unrestricted privileges.

Why it's needed: Many system-level tasks (installing software, modifying critical files, managing services) require root privileges.

Basic usage: Prepend sudo to the command. You will usually be prompted for *your own* user password.

Security Implications: Use sudo responsibly and only when necessary. Double-check commands, especially those that modify or delete files (like rm -rf).

Example:

sudo apt update  # (On Debian/Ubuntu systems)
sudo dnf upgrade # (On Fedora systems)

Action: A pipe (|) takes the standard output (stdout) of the command on its left and "pipes" it as the standard input (stdin) to the command on its right. This allows chaining commands.

Example:

ls -l /etc | grep cron  # Lists files in /etc and filters for "cron"
history | grep install    # Searches command history for "install"

Action: Redirects the standard output of a command to a file. If the file doesn't exist, it's created. **If the file already exists, its contents are overwritten.**

Example:

ls -la > my_directory_listing.txt

Action: Redirects the standard output of a command to a file, but instead of overwriting, it appends the new output to the end of the file. If the file doesn't exist, it's created.

Example:

date >> system_activity.log
echo "New log entry at $(date)" >> app.log

Action: Takes input for a command from a specified file instead of from the keyboard or another command's output. Less common for interactive beginner use but crucial for scripting.

Example:

sort < unsorted_names.txt
wc -l < my_document.txt  # Counts lines in the document

Action: Pressing the **Tab** key attempts to auto-complete what you're typing. If there's one possibility, it completes it. If multiple, pressing Tab twice usually lists them.

Why: Invaluable for speed and reducing typos.

Action: Interrupts (stops/kills) the currently running command or process in the foreground.

Action: If typed at an empty prompt, it logs you out of the current shell session (like typing exit). If a program is waiting for input, Ctrl+D often signifies "End-Of-File" (EOF).

Action: Clears the terminal screen, moving the current prompt to the top. Similar to typing the clear command.

Action: Moves the cursor to the absolute beginning of the current line.

Action: Moves the cursor to the end of the current line.

Action: Navigates through your command history. Press Up to see the previous command, Down to see the next.

Action: (Reverse-i-search) Searches backward through your command history as you type. Start typing part of a command you used previously, and it will show the most recent match. Press Ctrl+R again to cycle through older matches. Press Enter to execute the found command, or arrow keys to edit it.

Action: Suspends the current foreground process (sends it to the background, paused). You can bring it back with fg (foreground) or manage it with bg (background) and jobs. (More advanced)

Action: Deletes the word immediately before the cursor.

Action: Deletes all characters from the cursor to the beginning of the line.

Action: Deletes all characters from the cursor to the end of the line.