Add a PPC for "-j" perlrun option

This proposes a new perlrun option flag that handles JSON input.

Author: catouc

ppcs/ppc0034-j-perlrun-opt.md

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+# A short and accurate title
+
+## Preamble
+
+    Author:  Philipp Böschen <[email protected]>
+    Sponsor:
+    ID:      0034
+    Status:  Draft
+
+## Abstract
+
+This PPC suggests the implementation of a new perlrun option `-j` that works in conjunction with `-p` or `-n` to automatically feed the stdin that is parsed into `JSON::PP::decode_json($_);`
+A working example can be found at: https://github.com/Perl/perl5/pull/22718
+
+## Motivation
+
+Ultimately this change would make Perl another step further to being extremely useful in adhoc sysadmin tasks, a role that is currently covered by, usually, the `jq` tool.
+I personally have found that `jq`, while useful for quick extracts, becomes very cumbersome if you have to do conditional logic, which is where `perl -jnle` would shine since usually a simple `grep` or `map` can work wonders on getting good data quickly.
+JSON has largely become ubiquitous with modern API handling, so I feel like it's not overly specific to let Perl "natively" handle it.
+
+As the [PRs](https://github.com/Perl/perl5/pull/22718) discussion shows, there are of course alternatives, but none of them seem to be as accessible as a `-j` flag, especially if we are thinking of where `jq` is often applied:
+- On cloud-init scripts where Perl is present but not really considered
+- In a bare bones debugging environment it gets often pulled in, Perl would already be there
+
+## Rationale
+
+I have tested the aformentioned [PR](https://github.com/Perl/perl5/pull/22718) for a while at work and privately and found it quite useful in place of `jq`. It has one less dependency on my existing debugging kit and performs reasonably well.
+
+Any other proposed solutions always come with the catch that now I have to bring said solution along with me to the debugging target, be it a source filter or just a whole different tool written in Perl itself.
+
+There are some thoughts on the "-p" interaction for things that ingest JSON and don't want to produce a new JSON from it, I personally am unsure of what the ideal here would be right now.
+
+## Specification
+
+This would be an extension of https://perldoc.perl.org/perlrun.
+```pod
+=item -j
+
+causes Perl to consume the lines that "-n" provides to be fed into C<JSON::PP::decode_json($_);> to give access to line delimited JSON feeds as Perl hashes directly. This will fail with the usual errors from C<JSON::PP::decode_json> if the line that is read is not valid JSON.
+When used with both "-n" and -p", "-j" calls C<print JSON::PP::encode_json($_);> to properly print out JSON again.
+```
+## Backwards Compatibility
+
+This change can be backported into all versions that have a working `JSON::PP` module.
+
+## Security Implications
+
+This would open up a similar security exposure as any perl scripts have that use `JSON::PP`. Of course if this feature gets widely adopted into server bootstraps the criticality of `JSON::PP` becomes more vital over time.
+
+## Examples
+
+Structured logging is the obvious use case for this feature so you can for example force `journald` into line by line JSON mode and then parse it like so to list all root processes logs:
+```
+sudo journalctl -f -o json | ./perl -njle 'if ( $_->{"_GID"} == 0 ) {print $_->{"MESSAGE"}}'
+```
+
+This would work similarly for most structured logging applications that have somewhat all agreed on JSON being the format of choice.
+
+A quick example from parsing audit logs for Hashicorp Vault:
+
+```
+tail -f /var/log/vault/audit.log | perl -jnle 'if ( $_->{request}{client_id} eq "some_client" ) { print "$_->{request}{operation},$_->{request}{path}\n" }'
+update,auth/token/create
+...
+```
+
+## Prototype Implementation
+
+https://github.com/Perl/perl5/pull/22718 implements the full PPC while also passing all tests.
+
+## Future Scope
+
+There should be no additions would be that `JSON::PP` starts supporting different things.
+Some work could be done on formatting the output in various ways, like supporting pretty printing.
+
+## Rejected Ideas
+
+As mentioned above there has been some discussion around writing a custom Perl application/module that does similar things or using a source filter. All of these solutions fall a bit short on the portability of being in the main Perl runtime which is the allure of this flag since it would remove one more dependency from running systems.
+
+## Open Issues
+
+
+## Copyright
+
+Copyright (C) 2024, Philipp Böschen
+
+This document and code and documentation within it may be used, redistributed and/or modified under the same terms as Perl itself.
+