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Use ast-grep (sg) for AST-aware code search and rewrite across 25 languages. Trigger for structural code matching or deterministic codemods: find every function/call/class/import shaped like X, rewrite console.log to logger.info, strip `as any`, migrate require() to import, find empty catch blocks or missing await, and scan/apply YAML rules. Prefer this over rg/grep when the target is syntax shape rather than text; use rg for string contents, comments, filenames, or regex-style byte searches.
Passed 16 of 19 test cases with the skill, and 11 of 19 without it.
and 7 more in the full report
6 fixed13 passed either way3 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 6 test cases the skill fixed. Same model, same prompt, with and without the skill.
I want to run `sg run` to find all calls to `deprecatedMethod($$$)` in TypeScript files, but exclude all test files matching `**/*.test.ts`. What CLI flags should I pass to perform this search?
| Checked | Without skill | With skill |
|---|---|---|
| Specifies the TypeScript language flag --lang ts. | Missed | Passed |
| Passes --globs '!**/*.test.ts' to exclude test files. | Missed | Passed |
The instructions your model reads when the skill loads.
sg (also installed as ast-grep) is an AST-aware search and rewrite tool across 25 languages. It treats your pattern as code, parses it the same way it parses your project, and matches structurally. It is the right tool whenever your question depends on code shape rather than text bytes.
This skill ships a Python wrapper at scripts/ast_grep_helper.py and platform install scripts at install.sh (POSIX) and install.ps1 (Windows). The helper adds offline pattern validation, the two-pass write trick, and binary auto-resolution. Use it as your default entry point.
Use it whenever the user's question is about code structure, not bytes:
Request parameter."console.log(x) to logger.info(x)."as any cast."require(...) with import across the repo."Optional[X] to X | None."Switch to plain grep / rg when the question is text-shaped (string literal contents, comments, license headers, file names, cross-language regex). When in doubt, ask: "does the answer depend on the language's syntax tree, or just on the file's bytes?" If the former, ast-grep. If the latter, grep.
The wildcards are $VAR (one AST node) and $$$ (zero or more nodes). Regex syntax fails silently:
| You wrote | What ast-grep saw | What you wanted |
|---|---|---|
foo|bar | bitwise-or of foo and bar | run two separate searches |
.*foo | not parseable | $$$ foo (if $$$ is a list of nodes) or use rg |
\w+ | not parseable | $VAR to capture any identifier |
[a-z] | character class, not parseable | switch to rg |
The full anti-pattern table is in references/pitfalls.md §1. The helper's validate subcommand catches these mechanically — call it before debugging "no matches" by hand.
test cases passed, vs 11 / 19 without
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