Is it possible to load JSON data from STDIN while specifying code with --exec?

[Nikos Mouchtaris]

Hello,

I am trying to edit "inline" JSON streams, for instance as a part of a shell pipe line.

For those familiar, I am trying to replicate the functionality of JQ. In summary, this is having the ability to load JSON data from STDIN, while specifying a "transformation" as part of the command line arguments.

I have not found a way to use STDIN as data directly, because using STDIN negates the --exec argument.

This scenario forces the user to retreat to very weird shell tricks (store a whole JSON document in a variable so that it can be then passed as a --tla-* argument to the --exec program, or store it to intermediate files). I think this is awkward and non-scalable.

Is there something I am missing about this usage scenario?

Thank you,

Nikos

[Michael Lang]

It may kind of also be a 'shell trick' but you can achieve this by importing the special file /dev/stdin (at least on typical *nix systems):

$ jsonnet -e '(import "/dev/stdin") + {bar: 1}'
{"foo": 0}

^D
{
   "bar": 1,
   "foo": 0
}

[Nikos Mouchtaris]

Thank you Michael, those tricks are better than the ones I thought.

[Dave Cunningham]

There is indeed a kernel limit on how much data can be passed via other mechanisms, but importing /dev/stdin does work quite well.

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[Brett Viren]

Here is a variation on a theme. This keeps "/dev/stdin" out of the
Jsonnet code but at the expense of requiring a top level function:

$ echo '{a:42}' | jsonnet --tla-code-file x=/dev/stdin -e 'function(x) x'
{
"a": 42
}

-Brett.

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