Just require the modules and don't import the functions that have the same name; invoke them using their fully qualified names. E.g. if both Module1 and Module2 have foo:

require Module1;
require Module2;

Module1::foo();
Module2::foo();
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With eval, the above translates to:

my $mod = some_condition() ? 'Module1' : 'Module2';
eval "require $mod; ${mod}::foo()";
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TIMTOWTDI: I find the problem description admits too many different interpretations, leading to entirely different solutions; anyway, here's another possible form the solution could take:

use strict;
use warnings;

my $mod = shift;

require "$mod.pm";

eval "$mod->import(); 1" or die;  # modules all export 'foo' by defaul
+t
# eval "$mod->import( 'foo' ); 1" or die;

foo();
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Use the commented-out eval instead if you want to limit the functions that are imported.