interp: Add --value-output/-V option to do tovalue before output

[wader]

Idea is to skip display so that JSON is outputted instead of showing tree and hexdump etc.

[wader]

Not sure about this one yet, want something like it but is -V good? also should add documentation.

Demo:

$ fq '.headers[0].magic' format/mp3/testdata/test.mp3
   │00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11│0123456789abcdef01│
0x0│49 44 33                                             │ID3               │.headers[0].magic: "ID3" (valid)

$ fq -V '.headers[0].magic' format/mp3/testdata/test.mp3
"ID3"

$ fq -Vr '.headers[0].magic' format/mp3/testdata/test.mp3
ID3

$ fq '.headers[0].flags' format/mp3/testdata/test.mp3
   │00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11│0123456789abcdef01│.headers[0].flags{}:
0x0│               00                                    │     .            │  unsynchronisation: false
0x0│               00                                    │     .            │  extended_header: false
0x0│               00                                    │     .            │  experimental_indicator: false
0x0│               00                                    │     .            │  unused: 0

$ fq -V '.headers[0].flags' format/mp3/testdata/test.mp3
{
  "experimental_indicator": false,
  "extended_header": false,
  "unsynchronisation": false,
  "unused": 0
}

[peterwaller-arm]

👍 would have found this useful as a new user.

[wader]

Hey, yeap would be nice cli ergonomic to not have to do ... | tovalue. Any idea for something else than -V? also i see now that "description: "Output JSON value (don't display)" might not be very clear if you don't know that d etc is an alias for a display function.

I'll rebase the PR and fix the help description so you can try it if you want.

[peterwaller-arm]

My original expectation was for -r to do something like this, which would have been the parallel to jq. But if it's not reasonable to change -r's output at this point, your existing choice of UX looks reasonable to me.

[wader]

I was thinking of piggyback on -r but it would be confusing for strings i guess? then -r would both make a decode value string be outputted as JSON and be raw (not quoted)

[peterwaller-arm]

I'm unsure what you mean by 'do both' other than that it is a conflict and there is a choice to be made. I presume you'd want to preserve backwards compatible behaviour.

[wader]

For example:

$ fq '.path.to.a.string' file
<fancy hexdump/tree for string>
$ fq -V '.path.to.a.string' file
"some string"
$ fq -Vr '.path.to.a.string' file
some string

If we used -r for this then the -V case would not be possible for strings, would always be raw string and not JSON string.

[peterwaller-arm]

I think I understand what you're saying and it makes sense to me in my limited experience of fq and reasonable level of experience of jq.

[wader]

Updated the documentation a bit also. Maybe the -Vr combination should be mentioned somewhere

[wader]

Added -Vr to documentation and don't think i can come up with anything better than -V.

@peterwaller-arm Looks good? and thanks for bumping this issue 👍 had forgot about it

[wader]

Thanks for reviewing and sorry i modified some unrelated documentation, could not resist. The whole documentation probably needs an overhaul, parts have been written independently at different times so probably mixes styles etc.