You can't. At least except for trivial and mostly uninteresting scripts it is either not possible or is infeasible. Consider:

use strict;
use warnings;

my $count = 1;

while ($count < $ARGV[1]) {
    prn("$count\n");
}


sub prn {
    print $_[0];
}
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how do you deal with the loop limit being $ARGV1?