[Machine readable output from userland utilities] report

[David Chisnall]

On 2 Jun 2014, at 12:43, Zaro Korchev <zkorchev at mail.bg> wrote:

> At the moment both ls and vmstat are told to output JSON by specifying the -O option. However as I discussed with my mentor, this will be changed. The idea is to use an environment variable instead of the -O flag.

I don't like the idea of using an environment variable, because this is something that you might want to control on a per-command basis within a pipeline.  Especially with respect to incremental adoption, if you have some commands that will emit their default format, which is sent to sed / awk whatever, and some that will emit json natively, you don't want to suddenly have the output format from the legacy tools change once they gain machine-readable output support.

One *very* important thing to do is standardise the command-line flag that is used to specify the output format.  This may involve also converting some of the tools to use getopt_long if they don't already (lots of tools already use most single-digit options, so there's no possibility to define a single-letter flag that will be useable on all tools).  

> I understand your concerns about multi-threading. The idea is to have functions that serialize the object in an allocated buffer as it is constructed. Here is a more detailed example of what I mean:

It would be better to has some stream output API as the default.  If one back end only supports writing to buffers, then you can add an extra alloc / write / free sequence to hide it, but it would be good if the interface understands writing directly to file descriptors.  If the back end natively supports streaming, then you don't need to buffer the output.

David