IntroToLinux

13. Command Summary: Chapters 1-4

This chapter provides a comprehensive overview of all commands covered in the first four chapters of this course.

📚 Chapter 1: Introduction to Linux and Unix

No specific commands covered - This chapter focused on Linux history, philosophy, and distributions.

🐚 Chapter 2: The Linux Console and Terminal

Command	Description
`pwd`	Print Working Directory - shows your current location
`cd`	Change Directory - navigate to home directory
`cd <path>`	Change to specified directory
`cd ~`	Change to home directory
`cd ..`	Move up one directory level
`cd -`	Return to previous directory
`cd /`	Change to root directory

File Listing Commands

Command	Description
`ls`	List files and directories in current location
`ls -l`	List with detailed information (long format)
`ls -a`	List all files including hidden files (starting with .)
`ls -la`	List all files with detailed information
`ls -lh`	List with human-readable file sizes

File and Directory Operations

Command	Description
`touch <file>`	Create an empty file or update timestamp
`mkdir <dir>`	Create a new directory
`mkdir -p <path>`	Create nested directories (parent directories as needed)
`cp <source> <dest>`	Copy file from source to destination
`cp -r <source> <dest>`	Copy directory recursively
`mv <source> <dest>`	Move or rename file/directory
`rm <file>`	Remove/delete a file
`rm -i <file>`	Remove file with confirmation prompt
`rm -r <dir>`	Remove directory and its contents recursively
`rm -rf <dir>`	Force remove directory (use with caution!)
`rmdir <dir>`	Remove empty directory

Viewing File Contents

Command	Description
`cat <file>`	Display entire file contents
`cat -n <file>`	Display file with line numbers
`less <file>`	View file with pagination (recommended)
`more <file>`	View file with pagination (older tool)
`head <file>`	Display first 10 lines of file
`head -n <num> <file>`	Display first n lines of file
`tail <file>`	Display last 10 lines of file
`tail -n <num> <file>`	Display last n lines of file
`tail -f <file>`	Follow file changes in real-time (useful for logs)

Text Editing

Command	Description
`nano <file>`	Open file in nano text editor (beginner-friendly)

File Download

Command	Description
`wget <url>`	Download file from URL
`wget -O <name> <url>`	Download file with custom name

Getting Help

Command	Description
`man <command>`	Display manual page for command
`man -k <keyword>`	Search manual pages by keyword
`apropos <keyword>`	Search manual pages (same as man -k)
`<command> --help`	Display quick help summary for command
`<command> -h`	Display short help (some commands)

System Information

Command	Description
`whoami`	Display current username
`file <file>`	Determine file type

🌍 Chapter 3: Shell Environment and Variables

Environment Variable Commands

Command	Description
`env`	Display all environment variables
`set`	Display all variables (shell and environment)
`echo $VAR`	Display value of specific variable
`export VAR=value`	Create and export environment variable
`export VAR`	Export existing variable to environment

Common Environment Variables

Variable	Description
`$HOME`	User’s home directory path
`$USER`	Current username
`$PWD`	Present Working Directory
`$PATH`	Directories where shell looks for commands
`$PS1`	Primary shell prompt appearance
`$SHELL`	Path to current shell

Command History

Command	Description
`history`	Display command history
`history <n>`	Display last n commands
`history -c`	Clear command history
`history \\| grep <term>`	Search history for specific term
`!!`	Execute previous command
`!<n>`	Execute command number n from history
`!<text>`	Execute last command starting with text
`!$`	Use last argument from previous command

History Keyboard Shortcuts

Shortcut	Description
`Ctrl+R`	Reverse search through command history
`↑` (Up Arrow)	Navigate to previous command
`↓` (Down Arrow)	Navigate to next command
`Ctrl+P`	Previous command (same as Up Arrow)
`Ctrl+N`	Next command (same as Down Arrow)

Command Line Editing Shortcuts

Shortcut	Description
`Ctrl+A`	Move cursor to beginning of line
`Ctrl+E`	Move cursor to end of line
`Ctrl+U`	Delete from cursor to beginning of line
`Ctrl+K`	Delete from cursor to end of line
`Ctrl+W`	Delete word before cursor
`Ctrl+L`	Clear screen
`Ctrl+C`	Cancel current command

🔀 Chapter 4: I/O Redirection and Pipes

Output Redirection

Command	Description
`cmd > file`	Redirect stdout to file (overwrite)
`cmd >> file`	Redirect stdout to file (append)
`cmd 2> file`	Redirect stderr to file (overwrite)
`cmd 2>> file`	Redirect stderr to file (append)
`cmd &> file`	Redirect both stdout and stderr to file
`cmd > file 2>&1`	Redirect stderr to stdout, then to file
`cmd > /dev/null`	Discard stdout output
`cmd 2> /dev/null`	Discard stderr output
`cmd &> /dev/null`	Discard all output

Input Redirection

Command	Description
`cmd < file`	Use file as input for command
`cmd << EOF`	Here document - multi-line input until EOF
`cmd <<< "text"`	Here string - use string as input

Pipes

Command	Description
`cmd1 \\| cmd2`	Pipe output of cmd1 to input of cmd2
`cmd1 \\| cmd2 \\| cmd3`	Chain multiple commands together

Text Processing Commands

Command	Description
`head <file>`	Display first 10 lines
`head -n <num> <file>`	Display first n lines
`tail <file>`	Display last 10 lines
`tail -n <num> <file>`	Display last n lines
`tail -f <file>`	Follow file changes in real-time
`cat <file>`	Concatenate and display file contents
`cat -n <file>`	Display file with line numbers
`cat -A <file>`	Show non-printing characters
`tac <file>`	Display file in reverse line order
`more <file>`	Page through file content
`less <file>`	Advanced file pager with search capabilities
`strings <file>`	Extract readable text from binary files
`strings -n <num> <file>`	Extract strings with minimum length

Common Pipe Examples

Command	Description
`ls \\| wc -l`	Count files in directory
`ps aux \\| grep <process>`	Find specific process
`cat <file> \\| head -n 5`	Show first 5 lines of file
`history \\| tail -10`	Show last 10 commands
`du -sh */ \\| sort -hr`	Show directory sizes sorted
`ps aux \\| sort -k4 -nr`	Sort processes by memory usage

🎯 Quick Reference by Category

📂 File Management

ls, ls -la, cd, pwd, mkdir, touch, cp, mv, rm, rmdir

📖 File Viewing

cat, less, more, head, tail, strings

🔍 Information & Help

man, apropos, --help, whoami, file, which, type

🌍 Environment

env, set, export, echo $VAR

📜 History

history, !!, !n, !text, Ctrl+R

🔀 Redirection & Pipes

>, >>, 2>, &>, <, |

💡 Pro Tips

Use Tab Completion: Press Tab to auto-complete commands and file names
Combine Commands: Use pipes (|) to create powerful command chains
Save Output: Redirect output to files for later analysis
Search History: Use Ctrl+R to quickly find and reuse previous commands
Read Man Pages: When in doubt, man <command> is your best friend
Use Aliases: Create shortcuts for frequently used commands
Be Careful: rm -rf has no undo - always double-check before executing

Next: → Next Lesson
Previous: ← Key Takeaways
Lesson Home: ↑ Lesson 4: Redirects & Pipes
Course Home: ⌂ Introduction to Linux