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Essential CLI Commands Reference

Command-Line Interface (CLI) commands are fundamental for interacting with operating systems efficiently. Below is a structured guide to essential CLI commands, formatted for Joplin.

These commands help you move through the file system and check your location:

  • cd - Change directory (e.g., cd Documents moves to the "Documents" folder)
    • cd / - Navigate to the system's root directory (uses an absolute path)
    • cd ~ - Go to the current user's home directory
    • cd - - Switch to the previous directory you were working in
  • pwd - Print Working Directory (displays your exact location in the file system)

File & Directory Management​

Create, organize, and delete files and folders with these commands:

  • touch [filename] - Create a new empty file (e.g., touch notes.md creates a Markdown file)
  • mkdir [directory] - Make a new directory (e.g., mkdir Projects creates a "Projects" folder)
    • mkdir -p [path] - Create nested directories (e.g., mkdir -p Music/Jazz creates both "Music" and "Jazz")
  • ls - List contents of the current directory
    • ls -l - Show a detailed list (includes permissions, file size, and modification date)
    • ls -a - List hidden files/folders (those starting with a ., like .bashrc)
    • ls [path] - List contents of a specific directory (e.g., ls Downloads)
  • rm [item] - Remove a file or empty directory
    • rm --rf [item] - Force remove non-empty directories and all contents (use with extreme caution!)
  • cp [source] [destination] - Copy files/directories (e.g., cp report.pdf ~/Backups)
    • cp -r [source] [destination] - Copy directories recursively (including all contents)
  • mv [source] [destination] - Move or rename files/directories (e.g., mv oldname.txt newname.txt renames a file)

File Content Operations​

View, create, or edit file contents with these tools:

  • cat [filename] - Concatenate and display file contents (e.g., cat todo.txt shows your to-do list)
    • cat > [filename] - Write text to a file (overwrites existing content; press ctrl + d to save)
    • cat >> [filename] - Append text to a file (preserves existing content)
  • echo "[text]" - Print text to the terminal
    • echo "[text]" > [filename] - Write text directly to a file (overwrites)
    • echo "[text]" >> [filename] - Append text to a file (adds to the end)
  • nano [filename] / vim [filename] - Open a text editor to modify files (nano is beginner-friendly)

Output Redirection​

Control where command output is sent (instead of just the terminal):

  • > - Redirect output to a file (overwrites existing content)
    Example: ls -l > files_list.txt saves the detailed directory list to "files_list.txt"
  • >> - Append output to a file (adds to existing content instead of overwriting)
    Example: date >> activity_log.txt adds the current date/time to "activity_log.txt"

Terminal Controls​

Manage your terminal session with these shortcuts:

  • clear or ctrl + l - Clear the terminal screen
  • ctrl + c - Cancel the currently running command
  • ctrl + d - Exit the terminal or current mode (e.g., when editing with cat >)
  • exit - Close the terminal session entirely

System Information​

Get details about your system, user, and commands:

  • date - Show the current date and time
  • whoami - Display the username of the currently logged-in user
  • [command] --help - Show all options/flags for a command (e.g., ls --help)
  • man [command] - Open the manual page for a command (more detailed than --help; press q to exit)
  • df -h - Show disk space usage (in human-readable format, e.g., GB)
  • free -h - Display system memory (RAM) usage

Search & Filter​

Find files or text efficiently:

  • find [path] -iname "[pattern]" - Search for files/directories by name
    Example: find ~/Books -iname "*.pdf" finds all PDF files in your "Books" folder
  • grep "[text]" [filename] - Search for text within a file
    Example: grep "urgent" tasks.txt finds all lines with "urgent" in "tasks.txt"
  • [command] | grep "[text]" - Filter command output to show only lines with specific text
    Example: ls --help | grep "hidden" shows help info related to hidden files

Advanced Operations​

For complex tasks, use these commands:

  • touch file{001..100}.txt - Create multiple files (e.g., 100 files named "file001.txt" to "file100.txt")
  • chmod [permissions] [file] - Change file permissions (e.g., chmod 755 script.sh makes a script executable)
  • sudo [command] - Run a command with administrative (root) privileges (e.g., sudo apt update on Linux)
  • tar -czf [archive].tar.gz [files] - Create a compressed archive (e.g., tar -czf photos.tar.gz ~/Pictures)
  • tar -xzf [archive].tar.gz - Extract a compressed archive