Ldiff Guide

ldiff is a line difference visualizer that processes input lines, replacing repeated tokens with a substitute character for easy pattern recognition. It’s particularly useful for analyzing log files, command output, and any text with recurring patterns.

Core Concepts

Pattern Recognition

ldiff reads input line by line and compares each line to the previous one. When it finds tokens (words, numbers) that repeat from the previous line, it replaces them with a substitute character, making unique content stand out.

Token Types

The tool recognizes several types of tokens:

• Words: Alphanumeric sequences (hello, world, API)
• Numbers: Numeric sequences (2023, 404, 127)
• Separators: Punctuation and symbols (:, -, /, @, etc.)
• Whitespace: Spaces, tabs, and other whitespace
• ANSI Codes: Color codes and terminal escape sequences

Preservation

While replacing repeated tokens, ldiff carefully preserves:

• ANSI color codes - Terminal colors remain intact
• Separators and punctuation - Structure is maintained
• Whitespace - Original spacing and alignment
• Case sensitivity - Hello and hello are different tokens

Basic Operations

Simple Usage

# Read from stdin with default substitute character (░)
echo -e "hello world\nhello universe" | ldiff
# Output:
# hello world
# ░░░░░ universe

Custom Substitute Character

# Use a custom character for substitution
echo -e "test line\ntest another" | ldiff "*"
# Output:
# test line
# **** another

Reading from Files

# Process a file
ldiff < input.txt

# Process compressed logs
gunzip -c app.log.gz | ldiff

# Use with other commands
cat /var/log/system.log | tail -n 100 | ldiff

Log Analysis

System Logs

# Analyze system logs for patterns
tail -f /var/log/syslog | ldiff

# Find repeated patterns in auth logs
grep "Failed password" /var/log/auth.log | ldiff

Application Logs

# Monitor application logs in real-time
tail -f /var/log/myapp.log | ldiff

# Analyze historical logs
cat /var/log/myapp.log.1 | ldiff > patterns.txt

Web Server Logs

# Analyze access patterns
cat /var/log/nginx/access.log | ldiff "■"

# Find common request patterns
awk '{print $7}' /var/log/apache2/access.log | sort | ldiff

Example Log Analysis

# Input log lines:
# 2023-01-01 10:00:00 INFO Starting application
# 2023-01-01 10:00:01 INFO Loading configuration
# 2023-01-01 10:00:02 ERROR Failed to connect

cat app.log | ldiff
# Output:
# 2023-01-01 10:00:00 INFO Starting application
# ░░░░-░░-░░ ░░:░░:01 ░░░░ Loading configuration
# ░░░░-░░-░░ ░░:░░:02 ERROR Failed to connect

Command Analysis

File Listings

# Analyze directory structures
find /usr/local -type f | ldiff

# Compare file paths
ls -la /usr/bin/ | ldiff "●"

Process Lists

# Analyze running processes
ps aux | ldiff

# Monitor process changes
watch -n 1 "ps aux | head -20" | ldiff

Network Analysis

# Analyze network connections
netstat -tulpn | ldiff

# Monitor network activity
ss -tulpn | ldiff "█"

Advanced Features

Unicode Support

# Use Unicode characters for substitution
echo -e "hello world\nhello universe" | ldiff "█"
echo -e "test line\ntest another" | ldiff "▓"
echo -e "data point\ndata value" | ldiff "◆"

Piping and Redirection

# Save patterns to file
cat large.log | ldiff > patterns.txt

# Combine with other tools
cat access.log | grep "GET" | ldiff | head -50

# Chain multiple filters
journalctl -f | grep "ERROR" | ldiff "*" | tee error_patterns.log

Real-time Monitoring

# Monitor multiple log sources
tail -f /var/log/app1.log /var/log/app2.log | ldiff

# Monitor system activity
dmesg -w | ldiff

# Watch command output
watch -n 2 "df -h" | ldiff

Workflow Examples

Development Debugging

# 1. Start monitoring your application logs
tail -f /var/log/myapp.log | ldiff &

# 2. Reproduce the issue
./trigger_bug.sh

# 3. Analyze the pattern differences
# Repeated timestamp/process info is masked, errors stand out

# 4. Save interesting patterns
pkill tail
cat /var/log/myapp.log | tail -100 | ldiff > debug_patterns.txt

System Administration

# 1. Monitor system health
tail -f /var/log/syslog | ldiff "■" &

# 2. Check for unusual patterns
# Normal startup messages will show patterns
# Anomalies will show unique content

# 3. Investigate specific issues
grep "$(date +%Y-%m-%d)" /var/log/syslog | ldiff

Performance Analysis

# 1. Capture performance data
top -b -n 10 | ldiff > perf_patterns.txt

# 2. Analyze patterns
cat perf_patterns.txt | grep -v "░"

# 3. Find anomalies
# Look for lines without substitute characters

Configuration Patterns

Log Timestamp Formats

ldiff automatically handles various timestamp formats:

# ISO 8601: 2023-01-01T10:00:00Z
# Syslog: Jan 01 10:00:00
# Apache: [01/Jan/2023:10:00:00 +0000]
# Custom: 2023-01-01 10:00:00.123

Common Separators

The tool recognizes these separator patterns:

• Paths: /usr/local/bin → /░░░/░░░░░/bin
• URLs: https://api.example.com → ░░░░░://░░░.░░░░░░░.com
• Email: user@domain.com → ░░░░@░░░░░░.com
• IPs: 192.168.1.100 → ░░░.░░░.░.░░░

Integration with Other Tools

With grep

# Filter then analyze patterns
grep "ERROR" /var/log/app.log | ldiff

With awk

# Extract specific fields then analyze
awk '{print $1, $7}' /var/log/access.log | ldiff

With sort/uniq

# Find unique patterns
cat /var/log/app.log | ldiff | sort | uniq -c

With head/tail

# Analyze recent entries
tail -100 /var/log/app.log | ldiff

# Check first patterns
head -50 /var/log/app.log | ldiff

Safety Features

Signal Handling

• Broken Pipe: Gracefully handles when output is piped to head, less, etc.
• Keyboard Interrupt: Clean exit on Ctrl+C
• Input Validation: Validates substitute character input

Error Handling

• No Input: Clear error message when no stdin is provided
• Invalid Character: Warnings for multi-character substitutes
• File Permissions: Appropriate error messages for access issues

Best Practices

Performance

1. Large Files: Use with tail or head for very large files
2. Real-time: Use -f flag with tail for live monitoring
3. Memory: Tool processes line-by-line, memory usage is minimal

Analysis

1. Start Simple: Begin with default substitute character
2. Use Contrast: Choose substitute characters that stand out
3. Save Patterns: Redirect output to files for later analysis
4. Combine Tools: Use with grep, awk, and other text tools

Troubleshooting

1. No Patterns: If no substitution occurs, lines may be completely different
2. Too Much Substitution: Try processing smaller chunks
3. ANSI Issues: Some terminals may not display substitute characters correctly

Common Use Cases

Security Monitoring

# Monitor failed login attempts
tail -f /var/log/auth.log | grep "Failed" | ldiff

# Analyze access patterns
cat /var/log/nginx/access.log | ldiff | grep -v "░"

Application Monitoring

# Track API response patterns
tail -f /var/log/api.log | grep "response_time" | ldiff

# Monitor database queries
tail -f /var/log/mysql/slow.log | ldiff

System Analysis

# Analyze process startup patterns
dmesg | grep "systemd" | ldiff

# Monitor resource usage patterns
vmstat 1 | ldiff

See Also

• Installation Guide - How to install ldiff
• Usage Guide - General usage examples
• Scrap Guide - Manage temporary files
• Examples - More real-world examples