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Q&A

How do I choose the correct Perl module from these variations?

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When looking for Perl modules to handle JSON strings and/or documents, I found JSON::PP and JSON::XS. The documentation of JSON::PP says it is compatible with JSON::XS.

  1. What do these suffixes mean?
  2. Which one should I use and why?
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1 answer

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Perl modules sometimes have different implementations. The ::PP suffix means it's a "Pure Perl" implementation, where portability is the goal. The ::XS suffix is for the C-based implementation, where speed is the goal. Finally, JSON is just the top-level module itself, i.e. the one you actually use.

This site has a good description of their differences, but to quote:

JSON

JSON.pm is a wrapper around JSON::PP and JSON::XS - it also does a bunch of moderately crazy things for compatibility reasons, including extra shim code for very old perls [...]

JSON::PP

This is the standard pure perl implementation, and if you're not performance dependent, there's nothing wrong with using it directly [...]

JSON::XS

Ridiculously fast JSON implementation in C. Absolutely wonderful [...]

Just installing the top-level JSON module should work. The part about compatibility just means that both do the same thing, i.e. you should get the same output from both.

I installed the Perl JSON module a few years ago on a RHEL server I managed and it was a really straightforward process: just install (or build) the module from CPAN and done. (Note that this is just an example and you may want to look for more recent versions.)

Installing should be a simple case of either using the OS package manager (if in GNU+Linux), using the cpan utility, or building from source. The OS package manager is recommended because it helps keep things updated automatically.

To verify that it's installed, just try the following command from the terminal (assuming GNU+Linux):

$ perl -e 'use JSON;'

If it doesn't complain, then you should be good to go. If you get errors, then you should get ready to go in an adventure.

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