CLI

The cli/ sub-project builds a small wrapper around the interpreter and the WASI shim. Use it when you want to run a .wasm module from a shell — for quick experiments, for CI smoke tests against rustc-built binaries, or as a starting point for a longer-lived launcher.

First run

The committed examples/hello.wasm is a hand-written WAT fixture that calls env.putchar to print Hello, world!. From a checkout of this repo:

sbt 'cliJVM/run examples/hello.wasm'
# Hello, world!

For a real rustc-built WASI binary, you’ll need to give it a host directory to read from via --preopen:

mkdir -p /tmp/sandbox
echo "Hello from the host" > /tmp/sandbox/hello.txt

sbt 'cliJVM/run --preopen /tmp/sandbox:/sandbox \
                wasi/shared/src/test/resources/fixtures/real_rust_fileread.wasm'
# Hello from the host

Help output

$ wasm --help
wasm 0.4.0
Usage: wasm [options] <file> [<wasi-args>...]

  <file>                                       path to a .wasm module
  <wasi-args>...                               arguments passed to a WASI program's `_start` as argv[1..]
  -i, --invoke <export>                        name of the export to invoke (default: _start if exported, else main)
  -a, --args n1,n2,...                         comma-separated decimal i32 arguments to the export
  --list-exports                               print exported function names and exit (no invocation)
  -p, --preopen <host-path>:<virtual-name>     mount a host directory as a wasi preopen (repeatable)
  -e, --env <key>=<value>                      environment variable for the WASI program (repeatable)
  --stdin <path>                               redirect fd 0 from <path>
  --trace                                      install a counting Tracer; print totals to stderr after the run
  --validate-only                              parse + validate the module and exit; don't instantiate
  --help                                       print this help message
  --version                                    print version and exit

The CLI cross-builds on JVM, Scala.js (Node), and Scala Native — all three are wired up in build.sbt.

• Flags — every option, what it does, when to reach for it.
• Recipes — hand-written WAT, rustc-built WASI binaries, native binaries.