Feature request: Run once, then exit

[icopp]

onchange is very close to being usable as a general-purpose file runner across glob matches in a way I haven't seen with other npm tools.

Here's a quick example of the kind of thing I'm looking at, using https://github.com/drwpow/openapi-typescript to use a schema at docs/whatever.yml to generate src/generated/whatever.ts:

  "dev:openapi": "onchange -a 'docs/*.yml' -- openapi-typescript {{file}} --prettier-config . -o src/generated/{{fileBaseNoExt}}.ts",

If there was a flag to only run that once (without actually watching for further changes), I could use the same functionality in build steps without needing to break out any other script stuff.

[blakeembrey]

This sounds interesting, could be done. We might be able to use this with chokidar by closing the watcher on ready, otherwise we could make a PR to chokidar or use a different library with the same underlying glob support. I think the flag is only useful in combination with -a in this case, does that sound correct?

[icopp]

For this I'd think a new self-contained flag, maybe -r for 'run' or something.

[Qard]

I'd prefer something a little more obvious like --once, but other than that I like the idea. :)

[forivall]

Yeah, i was just thinking about this feature too -- luckily --outpipe solved the need i had for it.

onchange -v -o 'dot -Tpng | imgcat' *.dot -- cat '{{file}}' (where `cat '{{file}}' is actually a different command that generates graphviz, but nbd)

The alternative solution using once would be

while changed=$(onchange --once *.dot) ; do < dot -Tpng | imgcat ; done

[blakeembrey]

@forivall Can you help me understand your example a little more? It sounds like a different request from the while loop but maybe I don’t understand. Also not clear to me how outpipe helped you exit on ready, which is what @icopp was trying to do - basically run a command with each file as a glob instead of a file watcher.