Linux Command Reference

Quick reference for essential command-line tools used in system administration and development.

File Operations

ls - List Directory Contents

ls [options] [path]

Common Options:

• -l - Long format with details
• -a - Show hidden files
• -h - Human-readable file sizes
• -t - Sort by modification time
• -r - Reverse order

Examples:

ls -la          # List all files with details
ls -lh /var/log # Show log files with readable sizes
ls -lt          # Sort by newest first

cp - Copy Files

cp [options] source destination

Options:

• -r - Copy directories recursively
• -p - Preserve attributes
• -v - Verbose output
• -i - Prompt before overwrite

Examples:

cp file.txt backup.txt
cp -r dir1/ dir2/
cp -p *.conf /etc/backup/

mv - Move/Rename Files

mv [options] source destination

Examples:

mv oldname.txt newname.txt
mv *.log /var/logs/
mv -i file.txt /backup/  # Prompt before overwrite

rm - Remove Files

rm [options] file

Options:

• -r - Remove directories recursively
• -f - Force removal without prompts
• -i - Prompt before each removal
• -v - Verbose output

Examples:

rm file.txt
rm -rf directory/
rm -i *.tmp  # Prompt before deleting

Warning

rm -rf is destructive and cannot be undone. Always double-check paths.

Text Processing

grep - Search Text

grep [options] pattern [files]

Options:

• -i - Case insensitive
• -r - Recursive search
• -n - Show line numbers
• -v - Invert match (show non-matching)
• -c - Count matches

Examples:

grep "error" logfile.txt
grep -i "warning" *.log
grep -rn "TODO" /project/
grep -v "^#" config.conf  # Exclude comments

sed - Stream Editor

sed [options] 'command' file

Common Commands:

• s/old/new/ - Substitute text
• /pattern/d - Delete matching lines
• /pattern/p - Print matching lines

Examples:

sed 's/foo/bar/' file.txt           # Replace first occurrence
sed 's/foo/bar/g' file.txt          # Replace all occurrences
sed -i 's/foo/bar/g' file.txt       # Edit file in-place
sed '/^#/d' file.txt                # Delete comment lines
sed -n '/error/p' log.txt           # Print only error lines

awk - Text Processing

awk 'pattern {action}' file

Examples:

awk '{print $1}' file.txt           # Print first column
awk -F: '{print $1}' /etc/passwd    # Use : as delimiter
awk '$3 > 100' data.txt             # Print lines where column 3 > 100
awk '{sum+=$1} END {print sum}'     # Sum first column

System Information

ps - Process Status

ps [options]

Options:

• aux - All processes, user-oriented
• -ef - All processes, full format
• -u username - Processes for specific user

Examples:

ps aux
ps -ef | grep nginx
ps -u apache

top - Monitor Processes

top [options]

Interactive Commands (while running):

• q - Quit
• k - Kill process
• M - Sort by memory
• P - Sort by CPU
• u - Filter by user

df - Disk Space

df [options]

Options:

• -h - Human-readable sizes
• -T - Show filesystem type
• -i - Inode information

Examples:

df -h
df -hT /dev/sda1

du - Disk Usage

du [options] [path]

Options:

• -h - Human-readable
• -s - Summary only
• -a - All files
• --max-depth=N - Limit directory depth

Examples:

du -h /var/log
du -sh /home/*
du -h --max-depth=1 /

Network Commands

ping - Test Connectivity

ping [options] hostname

Options:

• -c N - Send N packets
• -i N - Wait N seconds between packets
• -s size - Packet size

Examples:

ping google.com
ping -c 4 192.168.1.1

curl - Transfer Data

curl [options] URL

Options:

• -O - Save with original filename
• -o filename - Save as filename
• -X METHOD - HTTP method
• -H "Header" - Add header
• -d data - POST data

Examples:

curl https://example.com
curl -O https://example.com/file.zip
curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' https://api.example.com

netstat - Network Statistics

netstat [options]

Options:

• -tuln - Show listening TCP/UDP ports with numbers
• -r - Show routing table
• -i - Show network interfaces

Examples:

netstat -tuln
netstat -r
netstat -i

File Permissions

chmod - Change Permissions

chmod [options] mode file

Numeric Mode:

• 4 = read (r)
• 2 = write (w)
• 1 = execute (x)

Examples:

chmod 755 script.sh     # rwxr-xr-x
chmod 644 file.txt      # rw-r--r--
chmod +x script.sh      # Add execute
chmod -w file.txt       # Remove write

chown - Change Owner

chown [options] owner[:group] file

Examples:

chown user file.txt
chown user:group file.txt
chown -R user:group directory/

Compression

tar - Archive Files

tar [options] archive files

Common Options:

• -c - Create archive
• -x - Extract archive
• -v - Verbose
• -f - File name
• -z - Gzip compression
• -j - Bzip2 compression

Examples:

tar -czf archive.tar.gz directory/      # Create compressed
tar -xzf archive.tar.gz                 # Extract compressed
tar -tvf archive.tar                    # List contents

gzip / gunzip - Compress Files

gzip [options] file
gunzip [options] file.gz

Examples:

gzip file.txt           # Creates file.txt.gz
gunzip file.txt.gz      # Extracts to file.txt
gzip -k file.txt        # Keep original

See Also

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