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Can someone explain exactly the usage recomandations regarding the 4 perl imports: do, import, use and require?

I'm looking for practical recommendations and keeping in mind possible issues that might arise in the context of mod_perl or something similar.

We all love simple examples, good ones!

So far the best resource I found was http://soniahamilton.wordpress.com/2009/05/09/perl-use-require-import-and-do/ , but this missed to consider the implications of mod_perl.

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How is Quick notes for me; not meant to be authoritative "the best resource" you found? –  Sinan Ünür Oct 3 '10 at 20:59
We have an entire chapter on this in Intermediate Perl. :) –  brian d foy Oct 5 '10 at 17:18
stackoverflow.com/questions/2180554/… This is a better post Please refer it. –  daa Oct 11 '11 at 9:02

3 Answers 3

up vote 11 down vote accepted

You should first read perldoc -f use and perldoc -f require.

They are excellent resources and explain how use works, how it invokes import and then require, and how you could theoretically implement require in terms of do.

If you have already read them, do you still have any specific open questions that the standard documentation doesn't cover well enough and you would like to have answered in more detail?

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do will call the code, no ifs, ands, or buts, at runtime. This is usually a bad idea, because if that's happening, you should really probably be putting it into a subroutine.

require will call exactly once and then no more, at runtime. it can do it for a package, too, in which case it will actually go find that package for you.

use does everything require does in the package case, then calls import in that package.

import is a function defined in a package. it gets called by use, but it's not otherwise special.

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You forgot to mention that use happens at compile time. use Foo; is equivalent to BEGIN { require Foo; Foo->import(); } –  daotoad Oct 3 '10 at 16:40

You can look at the mod_perl documentation for use(), require(), do()

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