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