Add shebang to executables?

[mpartel]

I was wondering, why not add #!/usr/bin/env node or something to all built executables (and chmod +x them)?

I don't see a downside, at least if this is optional/configurable, and this would be an easy fix for #17008/#7086: i.e. build-system self execution.

(Perhaps this is already possible, but I did not find a way to enable it.)

[mpartel]

Ok, not as easy as I thought. Such build tools need NODERAWFS to work (unless they're pure stdio), but the project as a whole might not want NODERAWFS.

So instead of just running with node, we'd probably need some emscripten-specific wrapper that injects NODERAWFS support before invoking node. I have no idea how difficult that would be.

Anyway, I did get Freetype (#17008) to build with this workaround:

emconfigure ./configure
env EMCC_CFLAGS=-sNODERAWFS=1 emmake make "$(pwd)/objs/apinames"
sed -i '1s;^;\#\!\/usr\/bin\/env node\n;' objs/apinames
chmod +x objs/apinames
emmake make

[sbc100]

I like this idea, and indeed we already do do this in some case. See

emscripten/tools/link.py

Lines 496 to 500 in 49ab23a

	logger.debug('adding `#!` to JavaScript file: %s' % cmd)
	# add shebang
	with open(script, 'w') as f:
	f.write('#!%s\n' % cmd)
	f.write(src)

.

Right now we only do this under certain circumstances, and we don't expose it as a user-facing option yet:

emscripten/tools/link.py

Lines 659 to 666 in 49ab23a

	autoconf = os.environ.get('EMMAKEN_JUST_CONFIGURE') or 'conftest.c' in state.orig_args or 'conftest.cpp' in state.orig_args
	if autoconf:
	# configure tests want a more shell-like style, where we emit return codes on exit()
	settings.EXIT_RUNTIME = 1
	# use node.js raw filesystem access, to behave just like a native executable
	settings.NODERAWFS = 1
	# Add `#!` line to output JS and make it executable.
	options.executable = True

[vadimkantorov]

I'm interested to run the Emscripten-produced JS/wasm with node to do CI-testing (e.g. I managed to compile Perl to wasm and would like to run some ./perl -e 'print("hello world\n");').

What are the necessary emcc/linker flags to be able to direcly run the produced executable with node without resorting to any node-specific loaders and so forth?

@sbc100 Are there any hacks to auto-add this shebang? Or are there any other options besides -s NODERAWFS=1 and sed like proposed above? or should I also add -s ENVIRONMENT=node?

[sbc100]

node is already part of the default -sENVIRONMENT but if you want to save on code size you can limit that output to only running on node using -s ENVIRONMENT=node yes (assuming you don't want to run on the web).