Structural Search

Structural Search

Search code by its abstract syntax tree (AST) structure. Finds semantic patterns that regex cannot match reliably.

Tools

| Tool | Command | Use For |

|------|---------|---------|

| ast-grep | sg -p 'pattern' | AST-aware code search |

Pattern Syntax

| Pattern | Matches | Example |

|---------|---------|---------|

| $NAME | Named identifier | function $NAME() {} |

| $_ | Any single node | console.log($_) |

| $$$ | Zero or more nodes | function $_($$$) {} |

Top 10 Essential Patterns

# 1. Find console.log calls
sg -p 'console.log($_)'

# 2. Find React hooks
sg -p 'const [$_, $_] = useState($_)'
sg -p 'useEffect($_, [$$$])'

# 3. Find function definitions
sg -p 'function $NAME($$$) { $$$ }'
sg -p 'def $NAME($$$): $$$' --lang python

# 4. Find imports
sg -p 'import $_ from "$_"'
sg -p 'from $_ import $_' --lang python

# 5. Find async patterns
sg -p 'await $_'
sg -p 'async function $NAME($$$) { $$$ }'

# 6. Find error handling
sg -p 'try { $$$ } catch ($_) { $$$ }'
sg -p 'if err != nil { $$$ }' --lang go

# 7. Find potential issues
sg -p '$_ == $_'           # == instead of ===
sg -p 'eval($_)'           # Security risk
sg -p '$_.innerHTML = $_'  # XSS vector

# 8. Preview refactoring
sg -p 'console.log($_)' -r 'logger.info($_)'

# 9. Apply refactoring
sg -p 'var $NAME = $_' -r 'const $NAME = $_' --rewrite

# 10. Search specific language
sg -p 'pattern' --lang typescript

Quick Reference

| Task | Command |

|------|---------|

| Find pattern | sg -p 'pattern' |

| Specific language | sg -p 'pattern' --lang python |

| Replace (preview) | sg -p 'old' -r 'new' |

| Replace (apply) | sg -p 'old' -r 'new' --rewrite |

| Show context | sg -p 'pattern' -A 3 |

| JSON output | sg -p 'pattern' --json |

| File list only | sg -p 'pattern' -l |

| Count matches | sg -p 'pattern' --count |

| Run YAML rules | sg scan |

When to Use

• Finding all usages of a function/method
• Locating specific code patterns (hooks, API calls)
• Preparing for large-scale refactoring
• When regex would match false positives
• Detecting anti-patterns and security issues
• Creating custom linting rules

Additional Resources

For complete patterns, load:

• ./references/js-ts-patterns.md - JavaScript/TypeScript patterns
• ./references/python-patterns.md - Python patterns
• ./references/go-rust-patterns.md - Go and Rust patterns
• ./references/security-patterns.md - Security vulnerability detection
• ./references/advanced-usage.md - YAML rules and tool integration
• ./assets/rule-template.yaml - Starter template for custom rules