the line $str->$str1($regexp); always passes $str as parameter to the subroutine.

$str is passed as first argument to the subroutine because you are using method invocation syntax. In particular, you are using the arrow operator: ->.

If you don't want $str passed as the first argument, you could use a symbolic reference:&{"${str}::${str1}"}($regexp).

use strict;
use warnings;

package XXX;

sub YYY {
    my ($x) = @_;
    print "hi there $x\n";
}

package main;

my $str = 'XXX';
my $str1 = 'YYY';

{
    no strict "refs";
    &{"${str}::${str1}"}(10);
}
[download]