kbrazil

There could be a major schema change that breaks the contract, but one of the nice things about JSON output is that it allows the creation of new fields without affecting downstream consumers.

That is, if I have a CLI program that spits out a list of IP addresses and one day I want to also output the corresponding dns names, I can simply add the "dns" field and existing pipelines will ignore the field and work just fine.

This is better than grep/awking/etc. unstructured text to STDOUT because, depending on how the author decides to add the new field, it can easily break existing pipelines that rely on the shape of the data to stay the same.

`jc` author here. I've been maintaining `jc` for nearly four years now. Most of the maintenance is choosing which new parsers to include. Old parsers don't seem to have too many problems (see the Github issues) and bugs are typically just corner cases that can be quickly addressed along with added tests. In fact there is a plugin architecture that allows users to get a quick fix so they don't need to wait for the next release for the fix. In practice it has worked out pretty well.

Most of the commands are pretty old and do not change anymore. Many parsers are not even commands but standard filetypes (YAML, CSV, XML, INI, X509 certs, JWT, etc.) and string types (IP addresses, URLs, email addresses, datetimes, etc.) which don't change or use standard libraries to parse.

Additionally, I get a lot of support from the community. Many new parsers are written and maintained by others, which spreads the load and accelerates development.

Also, `jc` automatically selects the correct /proc/file parser so you can just do `jc /proc/meminfo` or `cat /proc/meminfo | jc --proc` without specifying the actual proc parser (though you can do that if you want)

Disclaimer: I'm the author of `jc`.

Interesting - the proc-pid-parser actually parses that file name just fine:

    $ echo '2001 (bad) S 1 2 3 4 5) S 1888 2001 1888 34816 2001 4202496 428 0 0 0 0 0 0 0 20 0 1 0 75513 115900416 297 18446744073709551615 4194304 5100612 140737020052256 140737020050904 140096699233308 0 65536 4 65538 18446744072034584486 0 0 17 0 0 0 0 0 0 7200240 7236240 35389440 140737020057179 140737020057223 140737020057223 140737020059606 0' | jc --proc-pid-stat

    {"pid":2001,"comm":"bad) S 1 2 3 4 5","state":"S","ppid":1888,"pgrp":2001,"session":1888,"tty_nr":34816,"tpg_id":2001,"flags":4202496,"minflt":428,"cminflt":0,"majflt":0,"cmajflt":0,"utime":0,"stime":0,"cutime":0,"cstime":0,"priority":20,"nice":0,"num_threads":1,"itrealvalue":0,"starttime":75513,"vsize":115900416,"rss":297,"rsslim":18446744073709551615,"startcode":4194304,"endcode":5100612,"startstack":140737020052256,"kstkeep":140737020050904,"kstkeip":140096699233308,"signal":0,"blocked":65536,"sigignore":4,"sigcatch":65538,"wchan":18446744072034584486,"nswap":0,"cnswap":0,"exit_signal":17,"processor":0,"rt_priority":0,"policy":0,"delayacct_blkio_ticks":0,"guest_time":0,"cguest_time":0,"start_data":7200240,"end_data":7236240,"start_brk":35389440,"arg_start":140737020057179,"arg_end":140737020057223,"env_start":140737020057223,"env_end":140737020059606,"exit_code":0,"state_pretty":"Sleeping in an interruptible wait"}

But the "magic" signature doesn't recognize it:

    $ echo '2001 (bad) S 1 2 3 4 5) S 1888 2001 1888 34816 2001 4202496 428 0 0 0 0 0 0 0 20 0 1 0 75513 115900416 297 18446744073709551615 4194304 5100612 140737020052256 140737020050904 140096699233308 0 65536 4 65538 18446744072034584486 0 0 17 0 0 0 0 0 0 7200240 7236240 35389440 140737020057179 140737020057223 140737020057223 140737020059606 0' | jc --proc             
    jc:  Error - Parser issue with proc:
                 ParseError: Proc file could not be identified.
                 ...

I can fix the "magic" signature (regex) to account for such cases.

It doesn't look like jc suffers from this bug since the regex match is greedy:

    % echo '2001 (my (file) with) S 1888 2001 1888 34816 2001 4202496 428 0 0 0 0 0 0 0 20 0 1 0 75513 115900416 297 18446744073709551615 4194304 5100612 140737020052256 140737020050904 140096699233308 0 65536 4 65538 18446744072034584486 0 0 17 0 0 0 0 0 0 7200240 7236240 35389440 140737020057179 140737020057223 140737020057223 140737020059606 0' | jc --proc

    {"pid":2001,"comm":"my (file) with","state":"S","ppid":1888,"pgrp":2001,"session":1888,"tty_nr":34816,"tpg_id":2001,"flags":4202496,"minflt":428,"cminflt":0,"majflt":0,"cmajflt":0,"utime":0,"stime":0,"cutime":0,"cstime":0,"priority":20,"nice":0,"num_threads":1,"itrealvalue":0,"starttime":75513,"vsize":115900416,"rss":297,"rsslim":18446744073709551615,"startcode":4194304,"endcode":5100612,"startstack":140737020052256,"kstkeep":140737020050904,"kstkeip":140096699233308,"signal":0,"blocked":65536,"sigignore":4,"sigcatch":65538,"wchan":18446744072034584486,"nswap":0,"cnswap":0,"exit_signal":17,"processor":0,"rt_priority":0,"policy":0,"delayacct_blkio_ticks":0,"guest_time":0,"cguest_time":0,"start_data":7200240,"end_data":7236240,"start_brk":35389440,"arg_start":140737020057179,"arg_end":140737020057223,"env_start":140737020057223,"env_end":140737020059606,"exit_code":0,"state_pretty":"Sleeping in an interruptible wait"}

Edit: looks like I can tighten up the signature matching regex for the "magic" syntax per the issue found above. The greedy regex matching for the parser does seem to work fine, though.

Both ways work:

    $ jc ifconfig lo0

    $ ifconfig lo0 | jc --ifconfig

Good news - `jc` supports JSONLines output for many commands and file-types, too!

Also note that you are looking at plaintext output here. By default `jc` and other JSON filtering tools do syntax highlighting when outputting to the terminal so it's actually quite easy to read JSON these days.

Hi - jc author here. Just a couple points:

The casting to int/float is not done unless the underlying values are predictably documented to be numbers. There are rare cases where auto int/float conversions are done, but:

1) This is always documented, and

2) You can turn this functionality off via the —raw flag

Also, predictable schemas are documented with each parser. (e.g `jc -h —-arp`)

Feel free to open issues on GitHub if you would like to recommend parsers! Also, the latest version of jc supports parsing of /proc files, which may also help.