When is a subroutine reference in @INC called?

Question

As the title says, I\'m not clear on when such a subroutine will be called. From the require page at perldoc one can write:

push @INC, \\&my_sub;
sub my         


        

Answer 1

Perl calls a subroutine reference in @INC when it is traversing @INC to look for a module. That is, you'll trigger it when you try to load a module with use or require and Perl does not find that module in the preceding @INC locations.

BEGIN {
    push @INC, 
      sub { print "Oops: There was an error looking for $_[1]\n"; };
    }

eval "use Cat::Burglar";
eval "use Local::NotThere";
require Cat::Burglar;

You need to ensure that your subroutine reference is in @INC before you try to load the modules. Remember that use is a compile time feature and that require is a run time feature. As with adding other "regular" @INC entries, you probably want to do it in a BEGIN block as early as possible in your program.