ast-grep (sg)

ast-grep is a fast and polyglot tool for code searching, linting, and rewriting based on Abstract Syntax Trees (AST). It excels at structural search and replace where regex fails.

When to use

• Structural Search: Finding code based on structure (e.g., "all function calls to foo with 2 arguments") regardless of whitespace.
• Refactoring: Renaming variables, changing function signatures, or transforming code patterns safely.
• Linting: Creating custom rules to enforce code style or best practices.
• Code Analysis: Extracting information from codebases.

Quick Start

CLI Basics

# Search (pattern must be in single quotes)
ast-grep -p '$A + $B' --lang ts