# Command-Line Interface for `wesl-rs`
This is the frontend to the WESL compiler.
```
Commands:
check Check correctness of the source file
compile Parse the source and convert it back to code from the syntax tree
eval Evaluate a const-expression
exec Execute a WGSL shader function on the CPU
package Generate a publishable Cargo package from WESL source code
help Print this message or the help of the given subcommand(s)
```
## Compiling a shader
The CLI by default outputs the compiled shader to stdout.
Pipe or redirect the output to a file if needed.
```
wesl compile <path/to/main.wesl> > compiled.wgsl
```
WESL reads from stdin if no input is provided.
```
Flags allow customizing certain WESL features, see `wesl compile --help`.
## Evaluating a const-expression
The CLI allows evaluating const-expressions.
```
wesl eval "1 + abs(-1)"
expected output: 2
```
Provide a context program for the expression. Enable the `--no-strip` switch
to prevent dead-code elimination. Functions must be `@const` to be executed in
constant-expressions.
```
echo "@const fn return_two() -> u32 { return 2; }" | wesl eval --no-strip "return_two()"
// expected output: 2u
```
## Shader execution on the CPU (experimental)
The `wesl exec` command allow evaluation of entrypoint functions using the
WESL compiler. It allows inspecting specific return values and catching runtime
errors early. This functionality is experimental, not all built-in functions
are implemented.
```
wesl exec <path/to/shader.wesl> --entrypoint fs_main
```
You can bind binary buffers to bindings (`--ressource`) and set values of
pipeline-overridable constants (`--override`). You can also output the result as
a binary buffer following the WebGPU layout (`--out-binary`).
## Packaging shader libraries
The packaging command outputs to stdout the Rust codegen for the package. This
is the same output produced by [wesl::PkgBuilder] in `build.rs` files. Using the
CLI instead can be useful if you don't want to rely on a build.rs. Refer to the
[wesl] documentation about packaging for more information.
```
wesl package mypkgname <path/to/root.wesl> > mypkgname.rs
```
[wesl]: https://docs.rs/crate/wesl