Add CLI option to disable SVG file output

[terrybrash]

I use D2 in watch mode and don't want the generated SVG file.

It would be nice to have a CLI option to disable the output entirely, something like --no-output.

[alixander]

can you describe what you're doing? is it just the browser viewing that you want then?

[alixander]

hm i can see that use case.

i don't think there needs to be a CLI option though, you can just redirect to /dev/null. if you pass - for either the input or output, d2 reads from stdin or writes to stdout, respectively.

d2 -w hello.d2 - > /dev/null should watch without writing anything

[alixander]

cc @nhooyr for a second opinion

[nhooyr]

I agree that the redirect to /dev/null is sufficient but perhaps we should document it under --watch? It's certainly not intuitive as many people don't know about -.

Also, maybe worth adding a flag just for windows users where few really know the shell syntax. Like I would have no idea how to redirect to something like /dev/null lol

[bo-ku-ra]

Also, maybe worth adding a flag just for windows users where few really know the shell syntax. Like I would have no idea how to redirect to something like /dev/null lol

linux: /dev/null = windows: nul

c:\>d2.exe -w foobar.d2 - >nul

i think the windows user who does not know the syntax of the shell is not even able to write d2 sources :-p

[bo-ku-ra]

c:\>d2.exe -w foobar.d2 - >nul

habit (on windows)
nul: null
con: stdout

c:>d2.exe -w foobar.d2 con >nul

but d2 is not working now. (issues; dos redirection is not working. #541 )