Once you have compiled the dynamic library for your custom language, you need to register it in the `sgconfig.yml` file.

You need to add a new entry under the `customLanguages` key with the name of your custom language and some properties:

For example, to search for all occurrences of `print` in mojo files, you can run:

Or you can write a rule in yaml like this:

ast-grep has builtin support to search JavaScript and CSS inside HTML files.

Suppose we have an HTML file like below:

Running this ast-grep command will extract the matching CSS style code out of the HTML file!

ast-grep outputs this beautiful CLI report.

ast-grep works well even if just providing the pattern without specifying the pattern language!

You can also use ast-grep's [rule file](https://ast-grep.github.io/guide/rule-config.html) to search injected languages.

message: Prefer use appropriate custom UI instead of obtrusive alert call.

You can search the CSS inside JavaScript in the project configuration folder using this command:

It will produce the match result:

ast-grep has two ways to configure pattern strictness.

2. Using `strictness` in Pattern Object

Compared to the other two tools, ast-grep is lesser-known. In short it can do search and replace based on [abstract syntax trees](https://www.wikiwand.com/en/Abstract_syntax_tree). You can install it via [`cargo`](https://crates.io/crates/ast-grep) or [`brew`](https://formulae.brew.sh/formula/ast-grep).

cargo install ast-grep

brew install ast-grep

We need to provide a pattern, `-p`, for it to search as well as a rewrite string, `-r` to replace the old API with the new one. The command should be quite self-explanatory.

We suggest to add `-i` flag for `--interactive` editing. ast-grep will display the changed code diff and ask your decision to accept or not.

The command:

3. `SystemStage`

Let's write a command for this code migration.

-p '$APP.add_stage_after($STAGE, $OWN_STAGE, SystemStage::parallel())' \

-r '$APP.configure_set($OWN_STAGE.after($STAGE))' -i

However, I found some `add_stage_after`s are not replaced. Nah, ast-grep is [quite dumb](https://github.com/ast-grep/ast-grep/issues/374) that it cannot handle the optional comma after the last argument. So I used another query with a trailing comma.

-p 'app.add_stage_after($STAGE, $OWN_STAGE, SystemStage::parallel(),)' \

-r 'app.configure_set($OWN_STAGE.after($STAGE))' -i

Let's also write a pattern for it.

-p '$APP.add_system_to_stage($STAGE, $SYS)' \

-r '$APP.add_system($SYS.in_base_set($STAGE))' -i

Another change is to use `add_systems` instead of `add_system_set`. This is a simple pattern!

-p '$APP.add_system_set_to_stage($STAGE, $SYS,)' \

-r '$APP.add_systems($SYS.in_set($STAGE))' -i

* ast-grep’s YAML rule now has a new `transform` rule: `conversion`, which can change matches to different cases, such as upper, lower, or camelcase.

* ast-grep’s diff/rewriting now can fix multiple rules at once. See [commit](https://github.com/ast-grep/ast-grep/commit/2b301116996b7b010ed271672d35a3529fb36e56)

* ast-grep now prints matches with context like `grep -A -B -C`. See [issue](https://github.com/ast-grep/ast-grep/issues/464)

* JSON schema is added for better YAML rule editing. See [folder](https://github.com/ast-grep/ast-grep/tree/main/schemas)

* ast-grep now has official github action setup! See [action](https://github.com/ast-grep/action)

* Add python api support to allow users to write custom scripts using ast-grep. See [issue](https://github.com/ast-grep/ast-grep/issues/389)

* Support global language config to let users specify default options for each language. See [issue](https://github.com/ast-grep/ast-grep/issues/658)

* Improve napi documentation to help users understand how to use the native node module of ast-grep. See [issue](https://github.com/ast-grep/ast-grep/issues/682)

* Add ast-grep’s pattern/rule tutorial to teach users how to write effective and efficient patterns and rules for ast-grep. See [issue](https://github.com/ast-grep/ast-grep.github.io/issues/154)

* Add examples to ast-grep’s reference page to illustrate the usage and functionality of each option and feature. See [issue](https://github.com/ast-grep/ast-grep.github.io/issues/266)

* You can now use [`--inline-rules`](https://ast-grep.github.io/reference/cli/scan.html#inline-rules-rule-text) to run rules without creating any files on your disk! You can pass everything, pattern/rule/input, as a string. This is great for scripting!

* [`--stdin`](https://ast-grep.github.io/reference/cli/run.html#stdin) will always wait for your input so you can match some code written in your terminal.

* We have added support for three new languages: bash, php and elixir.

- **Tree-Sitter Version Bump**: We've upgraded to the latest tree-sitter version, enhancing parsing accuracy and speed. In future releases, we plan to leverage tree-sitter's [new Web Assembly grammar](https://zed.dev/blog/language-extensions-part-1) to support even more languages.

- **Scan and Diff Merge**: The [refactor](https://github.com/ast-grep/ast-grep/commit/c78299d2902662cd98bda44f3faf3fbc88439078) combines `CombinedScan::scan` and `CombinedScan::diff` for a more streamlined process.

language: JavaScript # please fully spell the language

playgroundLink: '[TODO]'

hasFix: true

ruleType: 'pattern' # 'pattern' or 'yaml'

-r '$A.char_indices()' \

-l rs

-r '$NUM.checked_ilog10().unwrap_or(0) + 1' \

-l rs

::: code-group

```bash [number]

```bash [string]

```bash [boolean]

:::

Using ast-grep can be as simple as running a single command in your terminal:

The command above will replace `var` statement with `let` for all <abbr title="ast-grep will also infer the language if you omit --lang">JavaScript</abbr> files.

ast-grep is a versatile tool for searching, linting and rewriting code in various languages.

* **Lint**: You can also use ast-grep as a linter. Thanks to the flexible rule configuration, adding a new customized rule is more intuitive and straightforward. It also has a pretty error reporting out of box

* **Rewrite**: ast-grep provide jQuery like utility methods to traverse and manipulate syntax tree. Besides, you can also use operators to compose complex matching from simple patterns.

In comparison to Babel, we can complete this hello-world task in ast-grep trivially

See [playground](/playground.html) in action!

ast-grep supports using [YAML](https://yaml.org/) to configure its linting rules to scan your code repository.

In your project root, add `sgconfig.yml` with content as below.

|- not-a-rule.yml

:::

ast-grep --help

:::danger Use `sg` on Linux

Linux has a default command `sg` for `setgroups`. You can use the full command name `ast-grep` instead of `sg`.

You can also use shorter alias if you want by `alias sg=ast-grep`.

:::

```shell [Full Command]

```shell [Short Form]

```shell [Without Lang]

:::tip Pro Tip

Pattern must be quoted by single quote `'` to prevent shell from interpreting `$` sign.

:::

--rewrite '$PROP?.()' \

--interactive \

-l ts \