thanks in advance for your answers novice

ROTFLMAO!
Sorry... not laughing at you, I was laughing at myself. I dowloaded your code and replaced the psuedocode with real code and boggled at why I kept getting errors to the effect of:

Undefined subroutine &B::just_print called at index.pl line 8.
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and then it dawned on me what was going on.

When you are doing a use B; you are pulling in the B perl compiler and not getting the expected results. Anyway....

I modified your example and came up with the following:

# The main code:
use A;
use Blooper;
 
 
foreach (0..1){
    A::just_print("hi")
        if $_;
    B::just_print("hello")
        if not $_;
  }
 
 
sub main_print(){
print @_;
}
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and

#A.pm
package A;
 
sub just_print{
    print @_;
    main::main_print();
}
 
1;
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and

#Blooper.pm
package B;
 
 
sub just_print {
    print @_;
    main::main_print();
}
 
1;
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and when the code is run I get:

hellohi
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as I would expect.

With all that in mind... what did you get for errors?