Linux Terminal

pwd                              # Print working directory
cd /path/to/directory            # Change directory
cd ~                             # Go to home directory
cd -                             # Go to previous directory
cd ..                            # Go to parent directory
cd ../..                         # Go up two directories

ls                               # List files (basic)
ls -la                           # List all files with details
ls -lh                           # Human-readable file sizes
ls -lt                           # Sort by modification time
ls -R                            # Recursive listing
tree                             # Directory tree structure
tree -L 2                        # Tree with 2 levels deep

home/
├── user/
│   ├── documents/
│   ├── downloads/
│   └── projects/
│       ├── webapp/
│       └── scripts/

# Absolute path (from root)
/home/user/documents/file.txt

# Relative path (from current directory)
./documents/file.txt

# Parent directory reference
../other_directory/file.txt

# Home directory shortcut
~/documents/file.txt

# Creating files
touch newfile.txt               # Create empty file
echo "Hello World" > file.txt   # Create file with content
cat > file.txt << EOF           # Multi-line file creation
Line 1
Line 2
EOF

# Copying files
cp source.txt destination.txt    # Copy file
cp -r source_dir/ dest_dir/     # Copy directory recursively
cp -a source.txt backup.txt      # Copy with permissions preserved

# Moving/Renaming files
mv old.txt new.txt              # Rename file
mv file.txt /path/to/location/  # Move file

# Removing files
rm file.txt                     # Remove file
rm -r directory/                # Remove directory recursively
rm -rf directory/               # Force remove directory

# File information
file filename                   # Determine file type
stat filename                   # Detailed file information
du -h filename                 # File size in human-readable format

# Finding files
find . -name "*.txt"           # Find .txt files in current directory
find / -name "config" 2>/dev/null  # Find files named config system-wide
locate filename                # Fast file location search
which command                  # Find command location
whereis command                # Find command binary and source

# Content searching
grep "pattern" file.txt        # Search for pattern in file
grep -r "pattern" /path/       # Recursive search
grep -i "pattern" file.txt     # Case-insensitive search
grep -n "pattern" file.txt     # Show line numbers

cat file.txt                    # Display entire file
less file.txt                   # Scrollable file viewer
head -n 10 file.txt            # Show first 10 lines
tail -n 10 file.txt            # Show last 10 lines
tail -f log.txt                # Follow log file in real-time

# Using nano (beginner-friendly)
nano filename                  # Open file in nano editor

# Using vim (powerful)
vim filename                   # Open file in vim editor
# vim basics:
# i  - Insert mode
# Esc - Normal mode
# :w  - Save
# :q  - Quit
# :wq - Save and quit
# :q! - Quit without saving

# Sorting
sort file.txt                  # Sort lines alphabetically
sort -r file.txt               # Reverse sort
sort -n file.txt               # Numeric sort
sort -u file.txt               # Unique lines only

# Removing duplicates
uniq file.txt                  # Remove adjacent duplicate lines
uniq -c file.txt               # Count occurrences

# Counting
wc file.txt                    # Word count (lines, words, characters)
wc -l file.txt                 # Line count only

# Extracting columns
cut -d',' -f1 file.csv         # Extract first column (CSV)
cut -d' ' -f1,3 file.txt      # Extract fields 1 and 3 (space delimited)

ps                              # Show current processes
ps aux                          # Show all processes in detail
ps -ef                          # Alternative process listing
top                             # Interactive process viewer
htop                            # Enhanced process viewer (if installed)

# Find specific process
ps aux | grep processname       # Find process by name
pgrep processname               # Find process ID

# Background processes
command &                       # Run command in background
jobs                            # List background jobs
fg %1                           # Bring job 1 to foreground
bg %1                           # Resume job 1 in background
kill %1                         # Kill background job

# Process termination
kill PID                        # Gracefully terminate process
kill -9 PID                     # Force kill process
killall processname             # Kill all processes by name

# Service management
systemctl status servicename     # Check service status
systemctl start servicename     # Start service
systemctl stop servicename      # Stop service
systemctl restart servicename   # Restart service
systemctl enable servicename     # Enable at boot

# Network configuration
ip addr                         # Show IP addresses (modern)
ifconfig                        # Show IP addresses (legacy)
ip route                        # Show routing table

# Network connectivity
ping google.com                 # Test connectivity
ping -c 4 google.com            # Send 4 packets only
traceroute google.com           # Trace route to destination
netstat -tulnp                  # Show listening ports
ss -tulnp                      # Modern netstat alternative

# Downloading files
wget https://example.com/file.zip  # Download file
curl -O https://example.com/file   # Download with curl

# File transfer
scp file.txt user@host:/path/      # Secure copy
rsync -av source/ dest/            # Efficient file sync

# DNS queries
nslookup domain.com                # DNS lookup
dig domain.com                     # Detailed DNS query
host domain.com                    # Simple DNS query

# History navigation
!!                              # Repeat last command
!$                              # Last argument of previous command
!*                              # All arguments of previous command
^old^new                        # Replace in last command

# Cursor movement
Ctrl+A                          # Move to beginning of line
Ctrl+E                          # Move to end of line
Ctrl+U                          # Delete from cursor to beginning
Ctrl+K                          # Delete from cursor to end
Ctrl+Y                          # Paste deleted text
Ctrl+L                          # Clear screen

# Tab completion
Tab                             # Autocomplete
Tab Tab                         # Show all possibilities

# Create aliases
alias ll='ls -la'               # Shortcuts for common commands
alias la='ls -la'
alias update='sudo apt update && sudo apt upgrade'

# Create functions
mkcd() {
    mkdir -p "$1"
    cd "$1"
}

# Add to ~/.bashrc for persistence
echo 'alias ll="ls -la"' >> ~/.bashrc
source ~/.bashrc                # Reload bash configuration

# Sequential execution
command1 && command2            # Run command2 only if command1 succeeds
command1 || command2            # Run command2 only if command1 fails
command1 ; command2             # Run command1, then command2

# Piping
command1 | command2             # Send output of command1 to command2
command | tee file.txt          # Display output and save to file

# Input/Output redirection
command > file.txt              # Redirect output to file
command >> file.txt             # Append output to file
command < file.txt              # Read input from file

# Basic regex with grep
grep '^word' file.txt          # Lines starting with "word"
grep 'word$' file.txt          # Lines ending with "word"
grep '[0-9]' file.txt         # Lines containing numbers
grep '\bword\b' file.txt      # Whole word "word"

# Advanced regex
grep -E 'word1|word2' file    # Multiple patterns
grep -E '^[A-Z]' file        # Lines starting with uppercase

#!/bin/bash
# Basic shell script structure

# Variables
NAME="Linux"
echo "Welcome to $NAME terminal"

# User input
read -p "Enter your name: " username
echo "Hello, $username!"

# Conditional statements
if [ -f "file.txt" ]; then
    echo "File exists"
else
    echo "File does not exist"
fi

# Loops
for i in {1..5}; do
    echo "Iteration $i"
done

while true; do
    echo "Press Ctrl+C to exit"
    sleep 1
done

# System monitoring
free -h                        # Memory usage
df -h                          # Disk usage
iostat                         # I/O statistics
vmstat                         # Virtual memory statistics
uptime                         # System uptime and load

# Process monitoring
htop                           # Interactive process viewer
iotop                          # I/O monitoring (if installed)
nethogs                        # Network usage by process (if installed)

# ~/.bashrc customizations
# Add these lines to your ~/.bashrc

# Custom prompt
PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

# Useful aliases
alias ..='cd ..'
alias ...='cd ../..'
alias grep='grep --color=auto'
alias ls='ls --color=auto'

# Environment variables
export EDITOR=vim
export HISTSIZE=10000
export HISTCONTROL=ignoredups

# Colors in terminal
export CLICOLOR=1
export LSCOLORS=GxFxCxDxBxegedabagaced

# Custom functions
extract() {
    if [ -f "$1" ]; then
        case "$1" in
            *.tar.bz2)   tar xjf "$1"     ;;
            *.tar.gz)    tar xzf "$1"     ;;
            *.bz2)       bunzip2 "$1"     ;;
            *.rar)       unrar x "$1"     ;;
            *.gz)        gunzip "$1"      ;;
            *.tar)       tar xf "$1"      ;;
            *.tbz2)      tar xjf "$1"     ;;
            *.tgz)       tar xzf "$1"     ;;
            *.zip)       unzip "$1"       ;;
            *.Z)         uncompress "$1"  ;;
            *.7z)        7z x "$1"        ;;
            *)           echo "'$1' cannot be extracted via extract()" ;;
        esac
    else
        echo "'$1' is not a valid file"
    fi
}

# Permission denied
sudo command                    # Run with elevated privileges
chmod +x script.sh             # Make script executable

# Command not found
which command                   # Check if command exists
echo $PATH                     # Check PATH variable
export PATH=$PATH:/new/path     # Add to PATH

# Disk space issues
df -h                          # Check disk usage
du -sh * | sort -hr           # Find large files

# Process issues
ps aux | grep runaway          # Find problematic processes
kill -9 PID                    # Force kill process

# Network issues
ping 8.8.8.8                  # Test basic connectivity
nslookup domain.com            # Test DNS resolution
netstat -tulnp                 # Check listening ports

# Enable debugging
bash -x script.sh              # Debug bash script
set -x                         # Enable debugging in current shell

# Error handling
set -e                          # Exit on error
set -u                          # Exit on undefined variable
set -o pipefail                # Exit on pipe failure

# Logging
command 2>&1 | tee log.txt     # Log both stdout and stderr
command >> logfile.txt 2>&1     # Append all output to log

# File operations
find, grep, sed, awk, sort, uniq, wc
# System monitoring
top, htop, ps, netstat, iostat
# Network tools
curl, wget, ping, traceroute, ssh
# Text editing
nano, vim, emacs
# Archiving
tar, zip, unzip, gzip, bzip2