Merge pull request #27 from copyleftdev/yet

Auto-merge PR #27

Author: copyleftdev

grep.md

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+# Ubuntu Grep Best Practices Cheatsheet
+
+## Basic Syntax
+```bash
+grep [options] pattern [file...]
+```
+
+## Essential Options
+| Option | Description | Example |
+|--------|-------------|---------|
+| `-i` | Case insensitive search | `grep -i "error" log.txt` |
+| `-r` or `-R` | Recursive search | `grep -r "TODO" /path/to/dir` |
+| `-n` | Show line numbers | `grep -n "pattern" file.txt` |
+| `-w` | Match whole words only | `grep -w "class" *.java` |
+| `-l` | Show only filenames | `grep -l "pattern" *.txt` |
+| `-c` | Count matches | `grep -c "error" log.txt` |
+| `-v` | Invert match (show non-matching) | `grep -v "^#" config.txt` |
+| `-E` | Extended regex support | `grep -E "word1|word2" file.txt` |
+
+## Best Practices
+
+### 1. Using Context Options
+```bash
+# Show 3 lines before match
+grep -B 3 "error" log.txt
+
+# Show 3 lines after match
+grep -A 3 "error" log.txt
+
+# Show 3 lines before and after
+grep -C 3 "error" log.txt
+```
+
+### 2. Color Output
+```bash
+# Enable color output
+grep --color=auto "pattern" file.txt
+
+# Add to ~/.bashrc for permanent color:
+export GREP_OPTIONS='--color=auto'
+```
+
+### 3. Excluding Directories
+```bash
+# Exclude specific directories
+grep -r "pattern" --exclude-dir={.git,node_modules,vendor} .
+
+# Exclude by pattern
+grep -r "pattern" --exclude-dir=".*" .
+```
+
+### 4. File Type Filtering
+```bash
+# Search only specific file types
+grep -r "pattern" --include="*.php" .
+
+# Multiple file types
+grep -r "pattern" --include="*.{js,jsx,ts,tsx}" .
+```
+
+### 5. Advanced Pattern Matching
+
+#### Regular Expressions
+```bash
+# Match start of line
+grep "^start" file.txt
+
+# Match end of line
+grep "end$" file.txt
+
+# Match any single character
+grep "h.t" file.txt
+
+# Match zero or more occurrences
+grep "wo*rd" file.txt
+
+# Match specific number of occurrences
+grep "o\{2\}" file.txt
+```
+
+#### Extended Regular Expressions (-E or egrep)
+```bash
+# Match either pattern
+grep -E "pattern1|pattern2" file.txt
+
+# Match one or more occurrences
+grep -E "o+" file.txt
+
+# Match zero or one occurrence
+grep -E "colou?r" file.txt
+```
+
+### 6. Performance Optimization
+
+#### For Large Files
+```bash
+# Stop after first match
+grep -m 1 "pattern" large_file.txt
+
+# Use binary grep for faster search
+grep -a "pattern" binary_file
+
+# Count matches without printing
+grep -c "pattern" large_file.txt
+```
+
+#### For Multiple Files
+```bash
+# Process files in parallel
+parallel "grep 'pattern' {}" ::: *.txt
+
+# Use find with grep
+find . -type f -exec grep "pattern" {} +
+```
+
+### 7. Error Handling
+```bash
+# Suppress error messages
+grep -s "pattern" /path/to/files/*
+
+# Show only error messages
+grep -q "pattern" file.txt 2>&1 >/dev/null
+```
+
+### 8. Common Use Cases
+
+#### Finding IP Addresses
+```bash
+grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" log.txt
+```
+
+#### Finding Email Addresses
+```bash
+grep -E "[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}" file.txt
+```
+
+#### Finding URLs
+```bash
+grep -E "https?://[A-Za-z0-9./]+" file.txt
+```
+
+## Tips for Daily Use
+
+1. **Use ripgrep (rg) for Better Performance**
+   - Install: `sudo apt install ripgrep`
+   - Usage: `rg "pattern"`
+
+2. **Create Aliases for Common Operations**
+   ```bash
+   # Add to ~/.bashrc
+   alias grepjs='grep -r --include="*.js"'
+   alias grepphp='grep -r --include="*.php"'
+   alias greperr='grep -i -r "error|warning|critical"'
+   ```
+
+3. **Use Process Substitution**
+   ```bash
+   # Search in command output
+   grep "pattern" <(command)
+   ```
+
+4. **Combine with Other Commands**
+   ```bash
+   # Find and grep
+   find . -type f -name "*.log" -exec grep "error" {} +
+
+   # Pipe with grep
+   ps aux | grep "[n]ginx"
+   ```
+
+## Common Pitfalls to Avoid
+
+1. Don't use grep without -r for directory searches
+2. Avoid using GREP_OPTIONS (deprecated)
+3. Remember to escape special characters in patterns
+4. Don't forget to use quotes around patterns with spaces
+5. Be careful with -R vs -r (symbolic links)
+
+## Debugging Tips
+
+1. Use `-v` to see what's being excluded
+2. Use `--debug` to see detailed matching information
+3. Use `-h` to suppress filenames in multi-file searches
+4. Add `-n` to show line numbers for easier reference