How do I use beta Perl modules from beta Perl scripts?

Question

If my Perl code has a production code location and "beta" code location (e.g. production Perl code us in /usr/code/scripts, BETA Perl code is in /usr/code/beta/scripts; production Perl libraries are in /usr/code/lib/perl and BETA versions of those libraries are in /usr/code/beta/lib/perl, is there an easy way for me to achieve such a setup?

The exact requirements are:

• The code must be THE SAME in production and BETA location.

  To clarify, to promote any code (library or script) from BETA to production, the ONLY thing which needs to happen is literally issuing cp command from BETA to prod location - both the file name AND file contents must remain identical.

• BETA versions of scripts must call other BETA scripts and BETA libraries (if exist) or production libraries (if BETA libraries do not exist)

• The code paths must be the same between BETA and production with the exception of base directory (/usr/code/ vs /usr/code/beta/)

• The scripts must be all under the same base directory but they may be in its sub-directories at arbitrary depth level (this precludes the classic use lib "$FindBin::Bin/../lib" solution from section 31.13. use lib of "Programming Perl")

I will present how we solved the problem as an answer to this question, but I'd like to know if there's a better way.

Answer 1

Our own solution was as follows:

• Have a library (let's call it BetaOrProd.pm)

  • The library MUST be included via "use BetaOrProd;" in every script
  • The library MUST be the very first use statement in every script after "use strict;" pragma (and "use warnings" if we use that). Including before any BEGIN blocks.
  • The library has a BEGIN block which contains most of the logic
  • That BEGIN block in the library checks the program's directory path (based off of $0 with absolute path applied)
  • If the directory path starts with /usr/code/beta, the program is deemed to run in BETA location, else in production
  • In either case, /usr/local/lib/perl is un-shifted to the beginning of @INC list
  • If BETA location, /usr/code/beta/lib/perl is un-shifted to the beginning of @INC list after that.
  • If BETA location, a special variable $isBETA (accessible by a accessor method exported from BetaOrProd.pm) is set to "BETA".

• Anytime a script/library needs to call another script, the path to the called script is calculated based on said accessor to $isBETA variable exported from BetaOrProd.pm

• Anytime a Perl library needs to be required or used, no special logic is needed - the @INC modified by BetaOrProd.pm takes care of knowing where the modules are to be imported from. If the module is present in BETA location, then the library from BETA location will be used by BETA script, else the library from prod location.

The main drawbacks of this approach are:

1. Requirement that every script must have "use BetaOrProd;" as the very first use statement in every script after "use strict;" pragma.

   Mitigated by the fact that our company requires every deployed piece of code to pass automated validator, which can check for this requirement.

2. Can't BETA test BetaOrProd.pm via /usr/code/beta/lib/perl . D'uh.

   Mitigated by very thorough unit and integration test of the library

Answer 2

I have had to use a similar configuration. The module was named after the project name, though, and could perform some other duties: loading some environment-specific configuration variables (locations of data, credentials for dev/prod databases, for example), processing some command-line arguments, and setting some other variables that were useful to most of the scripts in the project (the current date in YYYYMMDD format, whether the stock market was currently open, etc.)

Answer 3

I address this with FindBin:

use FindBin;
use lib "$FindBin::Bin/../lib";

Or, if taint mode is active:

use FindBin;
use lib ("$FindBin::Bin/../lib" =~ m[^(/.*)])[0];

Since this isn't dependent on any known or fixed paths, it allows for as many independent sets of the code on a single machine as I like, simply by creating a new copy of the project directory.

I maintain complete copies of all project modules in each development image of the project, but it sounds like you don't and instead rely on the beta copy falling back to the live copy's modules; a use lib /path/to/live/bin prior to the use libs above would handle that, or you could just link /path/to/live/bin into one of the directories on @INC so that it will always be available straight away.

If the live and beta versions will be run from different accounts, local::lib may also be worth looking at, but this doesn't really seem to be what it's intended for.

UPDATE: This does not work if the scripts themselves may live in multiple sub-directories of a given directory, but works otherwise.