--- name: cli description: Command line operations, Bash scripting, and terminal workflows category: tools priority: P1 tags: [cli, bash, shell, automation, terminal] subskills: - shell-basics - bash-scripting - process-management - text-processing --- # CLI Skill ## Purpose Navigate and control systems using command line efficiently. ## Core Principle **"The CLI is faster and more powerful than any GUI. Master it."** ## Shell Basics ### Navigation ```bash # Current directory pwd # List files ls ls -la # Detailed, hidden files ls -lh # Human readable sizes # Change directory cd /path/to/dir cd ~ # Home directory cd - # Previous directory # Create directory mkdir -p path/to/dir # -p creates parents # Remove rm file.txt rm -rf directory # Recursive, force (dangerous!) ``` ### File Operations ```bash # Copy cp file.txt file.backup # Move/rename mv old.txt new.txt # View file cat file.txt less file.txt # Scrollable head -n 10 file.txt # First 10 lines tail -n 10 file.txt # Last 10 lines tail -f file.txt # Follow (live updates) # Edit files nano file.txt vim file.txt ``` ## Bash Scripting ### Shebang & Permissions ```bash #!/bin/bash # ^^^ Shebang - tells system how to run script echo "Hello, World!" # Make executable chmod +x script.sh ./script.sh ``` ### Variables ```bash # Define variable NAME="World" # Use variable echo "Hello, $NAME!" # Environment variables export PATH=$PATH:/new/path # Command substitution FILES=$(ls | wc -l) echo "Found $FILES files" # Command arguments echo "First arg: $1" echo "All args: $@" ``` ### Conditionals ```bash if [ "$1" == "start" ]; then echo "Starting..." elif [ "$1" == "stop" ]; then echo "Stopping..." else echo "Usage: $0 {start|stop}" exit 1 fi ``` ### Loops ```bash # For loop for file in *.txt; do echo "Processing: $file" done # While loop count=0 while [ $count -lt 10 ]; do echo "Count: $count" ((count++)) done ``` ### Functions ```bash greet() { echo "Hello, $1!" } # Call function greet "World" ``` ## Process Management ### Viewing Processes ```bash # List all processes ps aux # Filter processes ps aux | grep node # Interactive process viewer htop top # Process tree pstree ``` ### Control Processes ```bash # Kill process by PID kill 1234 # Kill by name pkill node # Force kill kill -9 1234 ``` ### Background Processes ```bash # Run in background sleep 60 & # Bring to foreground fg # List background jobs jobs # Background specific job sleep 100 & # Job 1 sleep 200 & # Job 2 fg %1 # Bring job 1 to foreground ``` ## Text Processing ### Grep ```bash # Search pattern in file grep "pattern" file.txt # Recursive search grep -r "pattern" . # Case insensitive grep -i "pattern" file.txt # Invert match (show lines without pattern) grep -v "comment" file.txt # Show line numbers grep -n "pattern" file.txt # Show only filenames grep -l "pattern" -r . # Extended regex grep -E "error|warning" file.log ``` ### Sed (Stream Editor) ```bash # Replace text sed 's/old/new/g' file.txt # Delete lines sed '/pattern/d' file.txt # Print specific lines sed -n '10,20p' file.txt # In-place edit sed -i 's/old/new/g' file.txt ``` ### Awk ```bash # Print specific column awk '{print $1}' file.txt # Filter rows awk '$3 > 100' file.txt # Sum column awk '{sum += $1} END {print sum}' file.txt ``` ## Pipelines ### Chaining Commands ```bash # Find large files find . -type f -size +100M | du -sh # Count file types find . -type f -name "*.py" | wc -l # Find and process find . -name "*.log" -exec gzip {} \; # Complex pipeline cat file.txt | grep "error" | awk '{print $3}' | sort | uniq -c ``` ## Input/Output Redirection ```bash # Redirect output to file echo "Hello" > file.txt # Append to file echo "World" >> file.txt # Redirect error command 2> error.log # Redirect both command > output.log 2>&1 # Read from file command < input.txt # Pipe chain cat input.txt | grep "pattern" | wc -l > count.txt ``` ## SSH & Remote ### SSH Connection ```bash # Basic SSH ssh user@host # SSH with command ssh user@host "ls -la" # SSH with key ssh -i ~/.ssh/key.pem user@host # SSH tunnel ssh -L 8080:localhost:80 user@host ``` ### SCP (Secure Copy) ```bash # Copy to remote scp file.txt user@host:/path/ # Copy from remote scp user@host:/path/file.txt . # Copy directory scp -r directory/ user@host:/path/ ``` ## System Monitoring ### System Resources ```bash # Disk usage du -sh * df -h # Memory free -h # CPU top -bn 1 | head -20 # System info uname -a ``` ### Logs ```bash # View system log tail -f /var/log/syslog # View auth log sudo tail -f /var/log/auth.log # Journalctl (systemd) sudo journalctl -f sudo journalctl -u nginx ``` ## Automation ### Cron Jobs ```bash # Edit crontab crontab -e # Crontab format # * * * * * * command # │ │ │ │ │ # │ │ │ │ └─ Day of week (0-7, 0 = Sunday) # │ │ │ └───── Month (1-12) # │ │ └──────── Day of month (1-31) # │ └─────────── Hour (0-23) # └──────────────── Minute (0-59) # Examples 0 0 * * * /path/to/script.sh # Daily at midnight */15 * * * * /path/to/check.sh # Every 15 minutes 0 */2 * * * npm run backup # Every 2 hours ``` ### Watch ```bash # Watch command output watch -n 1 'ls -la' # Watch process watch -n 1 'ps aux | grep node' # Watch disk space watch -n 60 'df -h' ``` ## Power Tools ### Find ```bash # Find files by name find . -name "*.log" # Find by size find . -size +100M # Find by modification time find . -mtime -7 # Modified in last 7 days find . -mtime +30 -delete # Delete files older than 30 days # Find and execute find . -name "*.tmp" -delete find . -type f -exec chmod 644 {} \; ``` ### Xargs ```bash # Run command on each file find . -name "*.log" | xargs gzip # Parallel processing find . -name "*.py" | xargs -P 4 python -m py_compile # Limit items ls | xargs -n 1 head ``` ### Parallel (GNU Parallel) ```bash # Run on 4 cores in parallel find . -name "*.py" | parallel -j 4 python -m py_compile {} # Run on all CPU cores find . -name "*.sh" | parallel -j 0 bash -n {} ``` ## Role-Shifting When shifting **to** CLI mode: ``` "Switching to terminal mode..." → Use Bash commands → Chain with pipes → Automate with scripts ``` ## Gold Standard Integration ### Read-Back Verification - Verify script runs successfully - Check that output is correct - Confirm files were created/modified ### Executable Proof - Show script output - Demonstrate command results - Test in fresh shell --- **"The CLI is where experts work. GUIs are for tourists."**