doc: improve language argument

website/guide/introduction.md

@@ -18,7 +18,7 @@ Using ast-grep can be as simple as running a single command in your terminal:
 sg --pattern 'var code = $PAT' --rewrite 'let code = $PAT' --lang js
 ```
 
-The command above will replace `var` statement with `let` for all JavaScript files.
+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.
 
 ---
 
@@ -94,4 +94,4 @@ It is written in Rust, a native language and utilize multiple cores. (It can eve
 You can start from creating a one-liner to rewrite code at command line with minimal investment. Later if you see some code smell recurrently appear in your projects, you can write a linting rule in YAML with a few patterns combined. Finally if you are a library author or framework designer, ast-grep provide programmatic interface to rewrite or transpile code efficiently.
 
 ### Pragmatism
-ast-grep comes with batteries included. Interactive code modification is available. Linter and language server work out of box when you install the command line tool. ast-grep is also shipped with test à for rule authors.
+ast-grep comes with batteries included. Interactive code modification is available. Linter and language server work out of box when you install the command line tool. ast-grep is also shipped with test à for rule authors.

website/guide/quick-start.md

@@ -93,12 +93,21 @@ We can write this pattern to find all property checking code.
 $PROP && $PROP()
 ```
 
-It is a valid `ast-grep` pattern! We can use it in command line! Use `pattern` argument to specify our target
-and also `lang` is needed to tell ast-grep our target code language.
+It is a valid `ast-grep` pattern! We can use it in command line! Use `pattern` argument to specify our target.
+Optionally, we can use `lang` to tell ast-grep our target code language.
 
-```shell
-sg --pattern '$PROP && $PROP()' --lang ts TypeScript/src # path to TS source
+:::code-group
+```shell [Full Command]
+sg --pattern '$PROP && $PROP()' --lang ts TypeScript/src
+```
+```shell [Short Form]
+sg -p '$PROP && $PROP()' -l ts TypeScript/src
 ```
+```shell [Without Lang]
+# ast-grep will infer languages based on file extensions
+sg -p '$PROP && $PROP()' TypeScript/src
+```
+:::
 
 ## Rewrite
 
@@ -127,4 +136,4 @@ Hope you enjoy the power of AST editing in plain programming language pattern. O
 
 Links to catalog pages...
 
--->
+-->