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
