UPDATE: Just a few days after hitting publish on this blog, a few folks from the Perforce community shared a better way to output JSON data from p4 commands using the-ztag and-Mj flags:p4 -ztag -Mj changes -m3 | jq -s '.'

I recently ran acrossthis blog showing how to usejq to formatgit log output to JSON. Curious aboutjq and wanting to try a similar thing with Perforce, I was able to modify the example pretty easily.

This is whatp4 changes output looks like:

$ p4 changesChange 3 on 2023/07/20 by grepliz@test-local-01 'Add day1.pdf'Change 2 on 2023/07/20 by grepliz@test-local-01 'Add crazy.psd.'Change 1 on 2023/07/20 by grepliz@test-local-01 'Populated server with files '

Here is how you can format to JSON usingjq:

$ p4 changes | jq -R -s '[split("\n")[:-1] | map(split("\u0020")) | .[] | { "change": .[1], "author": .[5], "date": .[3], "message": .[6:length] | join(" ") }]'[  {    "change": "3",    "author": "grepliz@test-local-01"    "date": "2023/07/20",    "message": "'Add day1.pdf'"  },  {    "change": "2",    "author": "grepliz@test-local-01",    "date": "2023/07/20",    "message": "'Add crazy.psd.'"  },  {    "change": "1",    "author": "grepliz@test-local-01",    "date": "2023/07/20",    "message": "'Populated server with files '"  }]

I think the original blog I referred to gives a pretty good explanation of what is going on, but I find it helpful to write out what is going on for future reference (and for my future self!).

The input:p4 changes

I know the output ofp4 changes is being piped into thejq program and it is helpful that the output is delimited by a space character and is one line per changelist. This output produces the columns needed for programs likejq andawk.

The flags:jq -R -s

Thejq flags being used are nicelydocumented here.

--slurp/-s:
Instead of running the filter for each JSON object in the input, read the entire input stream into a large array and run the filter just once.

--raw-input/-R:
Don't parse the input as JSON. Instead, each line of text is passed to the filter as a string. If combined with --slurp, then the entire input is passed to the filter as a single long string.

Thejq filter

'[split("\n")[:-1] | map(split("\u0020")) | .[] | { "change": .[1], "author": .[5], "date": .[3], "message": .[6:length] | join(" ") }]'

This is where all the magic happens. There are basically 4 sections to this filter.

• split("\n")[:-1]

This says to split on newlines. If we were to stop here, we would get an array of the changelists.
Example:

p4 changes | jq -R -s 'split("\n")[:-1]'[  "Change 3 on 2023/07/20 by grepliz@test-local-01 'Add day1.pdf'",  "Change 2 on 2023/07/20 by grepliz@test-local-01 'Add crazy.psd.'",  "Change 1 on 2023/07/20 by grepliz@test-local-01 'Populated server with files '"]

• map(split("\u0020"))

This tells the filter to map and split on the space character.
When combined with #1 above it would look like this:

p4 changes | jq -R -s 'split("\n")[:-1] | map(split("\u0020"))'[  [    "Change",    "3",    "on",    "2023/07/20",    "by",    "grepliz@test-local-01",    "'Add",    "day1.pdf'"  ],  [    "Change",    "2",    "on",    "2023/07/20",    "by",    "grepliz@test-local-01",    "'Add",    "crazy.psd.'"  ],  [    "Change",    "1",    "on",    "2023/07/20",    "by",    "grepliz@test-local-01",    "'Populated",    "server",    "with",    "files",    "'"  ]]

• .[]

This creates arrays of the values such that we can iterate over it. The following is from the documentation:

Array/Object Value Iterator: .[]
If you use the .[index] syntax, but omit the index entirely, it will return all of the elements of an array. Running .[] with the input [1,2,3] will produce the numbers as three separate results, rather than as a single array.

You can also use this on an object, and it will return all the values of the object.

p4 changes | jq -R -s 'split("\n")[:-1] | map(split("\u0020")) | .[]'[  "Change",  "3",  "on",  "2023/07/20",  "by",  "grepliz@test-local-01",  "'Add",  "day1.pdf'"][  "Change",  "2",  "on",  "2023/07/20",  "by",  "grepliz@test-local-01",  "'Add",  "crazy.psd.'"][  "Change",  "1",  "on",  "2023/07/20",  "by",  "grepliz@test-local-01",  "'Populated",  "server",  "with",  "files",  "'"]

• { "change": .[1], "author": .[5], "date": .[3], "message": .[6:length] | join(" ") }

Finally, this section gives us the desired JSON shape of each changelist and by wrapping the whole thing (the whole jq filter) with[], we get the final array.