Linux Command Line Basics

Opening the Terminal

The terminal (also called a shell, console, or command line) is a text-based interface where you type commands for the operating system to execute. On most Linux desktops, you can open a terminal with the keyboard shortcut Ctrl + Alt + T, or by searching for "Terminal" in your application menu.

When you open the terminal, you will see a prompt that typically looks like this:

username@hostname:~$

This tells you your username, the computer's hostname, the current directory (~ means your home directory), and the privilege level ($ for normal user, # for root).

Navigation Commands

Navigating the file system is the most fundamental skill. These commands let you move around and see what is where:

Understanding ls Options

The ls command becomes much more powerful with flags:

# Long format with details (permissions, owner, size, date)
ls -l

# Show hidden files (those starting with a dot)
ls -a

# Combine both: long format + hidden files
ls -la

# Human-readable file sizes (KB, MB, GB)
ls -lh

# Sort by modification time (newest first)
ls -lt

# Recursive listing (include subdirectories)
ls -R

File Management

These commands let you create, copy, move, rename, and delete files and directories:

Viewing and Editing Files

Reading file contents is something you will do constantly on Linux:

# Display entire file contents
cat filename.txt

# View file with pagination (scroll with Space, quit with q)
less filename.txt

# Display first 10 lines (or specify a number)
head filename.txt
head -20 filename.txt

# Display last 10 lines
tail filename.txt

# Follow a file in real-time (great for logs)
tail -f /var/log/syslog

# Count lines, words, and characters
wc filename.txt
wc -l filename.txt    # lines only

Text Editors in the Terminal

Linux offers several terminal-based text editors:

• nano — Beginner-friendly editor with on-screen shortcut hints. Open with nano filename.txt. Save with Ctrl+O, exit with Ctrl+X.
• vim — Powerful modal editor with a steep learning curve. Highly efficient once mastered. Open with vim filename.txt. Press i to enter insert mode, Esc then :wq to save and quit.
• vi — The classic Unix editor, available on virtually every system. Similar to vim but with fewer features.

Searching and Finding

Quickly locating files and content is essential for efficient system management:

# Find files by name
find /home -name "*.txt"

# Find files modified in the last 7 days
find /var/log -mtime -7

# Find files larger than 100MB
find / -size +100M -type f

# Search for text inside files
grep "error" /var/log/syslog

# Recursive search through directories
grep -r "function" /home/user/project/

# Case-insensitive search
grep -i "warning" logfile.txt

# Show line numbers with matches
grep -n "TODO" *.py

Pipes and Redirection

Pipes and redirection are fundamental concepts that let you chain commands and control input/output:

Pipes ( | )

Pipes send the output of one command as input to another:

# Count number of files in a directory
ls -1 | wc -l

# Find a specific process
ps aux | grep nginx

# Sort and display unique lines
cat names.txt | sort | uniq

# View long output with pagination
dmesg | less

Redirection

# Write output to a file (overwrites)
echo "Hello World" > output.txt

# Append output to a file
echo "Another line" >> output.txt

# Redirect errors to a file
command 2> errors.log

# Redirect both output and errors
command > output.txt 2>&1

# Discard output completely
command > /dev/null 2>&1

System Information Commands

# Display system information
uname -a

# Show disk usage
df -h

# Show directory size
du -sh /var/log

# Display memory usage
free -h

# Show running processes
ps aux
top
htop    # interactive (install separately)

# Display network information
ip addr show
ip route show

# Show current date and time
date

# Show system uptime
uptime

# Show who is logged in
who
w

Helpful Keyboard Shortcuts

Getting Help

Linux has excellent built-in documentation:

# Manual pages - comprehensive documentation
man ls
man grep

# Quick help - most commands support --help
ls --help
grep --help

# One-line command description
whatis ls

# Search for commands by description
apropos "copy files"

# Info pages (alternative to man)
info coreutils