The Ultimate Guide to Unix/Linux Commands with Examples

 

Unix/Linux is a powerful operating system, widely used by developers and system administrators. Mastering its command-line tools enhances productivity and helps you manage files, processes, permissions, and systems efficiently. This guide categorizes the most essential Unix/Linux commands by function — with practical examples included.

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📁 File and Directory Commands

Listing and Navigating Directories

ls                # List files and directories
ls -al            # Long list format with hidden files
ls -lt            # Sort by last modified time
cd dir            # Change to directory 'dir'
cd                # Go to home directory
pwd               # Print working directory

File Viewing and Creation

cat > file.txt    # Create file and input content
cat file.txt      # Display content
more file.txt     # Page-by-page output
head file.txt     # First 10 lines
tail file.txt     # Last 10 lines
tail -f file.txt  # Continuously output file updates

File and Directory Operations

touch file.txt           # Create or update a file
rm file.txt              # Delete a file
rm -r dir                # Recursively delete directory
rm -f file.txt           # Force delete
rm -rf dir               # Forcefully delete directory
cp file1 file2           # Copy file
cp -r dir1 dir2          # Copy directory
mv file1 file2           # Move or rename
ln -s file link          # Create symbolic link
mkdir dir                # Create new directory

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⚙️ Process Management

View Running Processes

ps                      # Current user's processes
top                     # Real-time process viewer

Terminate Processes

kill PID                # Kill specific process
killall proc            # Kill all named processes
pkill pattern           # Kill matching processes

Job Control

bg                      # Resume stopped job in background
fg                      # Resume job in foreground
fg %1                   # Bring job 1 to foreground

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🔒 File Permissions

Permission Basics

Each permission level is represented numerically:

• r (read) = 4

• w (write) = 2

• x (execute) = 1

Change File Permissions

chmod 755 filename      # Owner: rwx, Group: r-x, Others: r-x
chmod 777 filename      # Full permissions to all
ls -ltr                 # View permissions in long list

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🔍 Search and Find

Using grep to Search Patterns

grep "this" demo.txt            # Search 'this' in file
grep -r "ramesh" *              # Recursive search
grep -l "this" demo_*           # Only filenames with match

Count Lines

wc -l file                      # Count lines
grep -w "pattern" -c file       # Count lines with exact match

Locate Files and Processes

locate filename                 # Fast find (uses updatedb)
find . -name "file*"            # Search in current dir
pgrep pattern                   # Find process IDs by name

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🖥️ System Information

General System Details

date                           # Current date and time
cal                            # Current month calendar
uptime                         # System uptime
w                              # Who is logged in
whoami                         # Current user
finger user                    # User info
uname -a                       # Kernel and system info

CPU & Memory

cat /proc/cpuinfo              # CPU details
cat /proc/meminfo              # Memory details

Disk and Resource Usage

df -h                          # Disk space usage
du -sh *                       # Directory sizes
free -h                        # Memory usage

Locate Executables

whereis app                    # Locate binaries/source/docs
which app                      # Show default command path

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📦 Compression and Archives

Tar Commands

tar cf file.tar file           # Create tar
tar xf file.tar                # Extract tar
tar czf file.tar.gz files      # Tar with gzip
tar xzf file.tar.gz            # Extract gzipped tar
tar cjf file.tar.bz2 files     # Tar with bzip2
tar xjf file.tar.bz2           # Extract bzipped tar

Gzip Compression

gzip file                      # Compress file
gzip -d file.gz                # Decompress file

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🌐 Networking Commands

Basic Network Utilities

ping example.com               # Check connectivity
whois openai.com               # Domain ownership info
dig openai.com                 # DNS lookup
dig -x 8.8.8.8                 # Reverse DNS lookup
wget http://file.com/file.txt # Download file
wget -c file                   # Resume stopped download

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⌨️ Keyboard Shortcuts & Command History

Handy Shortcuts

• Ctrl + C: Terminate current command

• Ctrl + Z: Pause current command

• Ctrl + D: Logout/EOF

• Ctrl + W: Delete word

• Ctrl + U: Delete entire line

• Ctrl + R: Reverse search command history

• !!: Repeat last command

• exit: Logout

Command History

history                        # Show command history

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✍️ Practical File Editing and Examples

Create a File

touch fruits.txt

View and Edit a File

cat fruits.txt
vi devops.txt

Add this content:

Apple
Mango
Banana
Cherry
Kiwi
Orange
Guava

Save and Exit in vi:

• Press i to insert

• Press Esc, then type :wq and press Enter

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📄 Specific Line Display

View Top/Bottom Lines

head -3 filename               # First 3 lines
tail -3 filename               # Last 3 lines

Compare Two Files

diff file1 file2              # Show differences

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✅ Summary of Categories

Category	Commands
📁 File Management	ls, cd, pwd, cp, mv, rm, touch
🔄 Process Management	ps, top, kill, fg, bg, pkill
🔒 Permissions	chmod, ls -ltr
🔍 Searching	grep, find, locate, pgrep
🖥️ System Info	date, uptime, uname, df, free
📦 Compression	tar, gzip
🌐 Networking	ping, wget, dig, whois
⌨️ Shortcuts	Ctrl+C, !!, Ctrl+R, exit