This post adds to almut's post in case you want more details on compilation and execution order. If you don't, then skip this post. 

use Module;

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is the same as 
BEGIN {
    require Module;
    Module->import();
}

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(In fact, in existing versions of Perl, the parser can't tell the difference and that's the source of a bug unrelated to this post.)

BEGIN blocks are execute as soon as they are compiled, so 

push (@INC, "D:\\Perl\\site\\lib");
use DBI;

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is executed as follows:
  1. push (@INC, "D:\\Perl\\site\\lib"); is compiled.
  2. require DBI; is compiled.
  3. DBI->import(); is compiled.
  4. require DBI; is executed (by virtue of being in a BEGIN block).
  5. DBI->import(); is executed (by virtue of being in a BEGIN block).
  6. The rest of the program is compiled.
  7. The compilation phase ends and the execution phase begins.
  8. push (@INC, "D:\\Perl\\site\\lib"); is executed.
  9. The rest of the program is executed.

As you can see, the modification of @INC happens much much too late.

In reply to Re: Cant locate DBI in @INC (BEGIN) by ikegami
in thread Cant locate DBI in @INC by Irishboy24

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