To me, the 3 of them seem to do exactly the same : give the information of "where are these sources that i need". PERL5LIB does it through an environment variable, lib does it in each source file, and -I does it on the command line. Any other difference?

Ultimately there's only one way of telling Perl where to search for modules: the global @INC array - it's a list of directories that Perl uses to search for libraries. PERL5LIB and "-I" are just ways of informing Perl to pre-populate @INC with certain directories.

And use lib just manipulates @INC while your code is being compiled. (You can look at lib.pm and see what's going on - there's nothing especially mysterious.)

They're each useful in different ways.

If you have some paths that you always (or nearly always) want Perl to search in, then use the environment variable. You can set it in your .bashrc/.tcshrc or some other script that is executed as soon as you log in, and forget all about it.

use lib is useful if you want to hard-code library paths that will be searched for specific scripts. It's not especially good for code you hope to publish for other people to install and use though, because they might plan on installing modules somewhere else. Relative paths can also be problematic with use lib because they are treated relative to the directory Perl was executed in, not relative to the file in which the use lib appears. (There are modules like "lib::abs" which improve the situation.)

The -I argument for perl is useful for most other situations. It tends to be what I use when I'm testing Perl modules I've written and intend to publish. I'll use a directory structure like this:

  p5-my-module/
        lib/
              My/
                    Module.pm
        examples/
              demo.pl
        t/
              00basic.t
              01advanced.t
        xt/
              01pod.t
              02pod_coverage.t

Then I'll have my terminal mostly in p5-my-module, and I can run things like:

perl -Ilib t/00basic.t
perl -Ilib examples/demo.pl

I find that use lib can be handy used within test suites to help the test cases find additional testing modules (which might be inside "p5-my-module/t/lib/"). This is because although use lib isn't great for stuff that's getting installed on other people's machines, test suites don't get installed, and they are run in a very predictable way.

In reply to Re^3: Developing a module, how do you do it ? by tobyink
in thread Developing a module, how do you do it ? by mascip

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