#!/usr/bin/perl

open my $IN2, "<", "foo.txt" or die;

while (my $seq = <$IN2>) {
    print "line: '$seq'\n";
}

##</code><code>##

$ perl -MO=Deparse ./808927.pl
die unless open my $IN2, '<', 'foo.txt';
while (defined(my $seq = <$IN2>)) {
    print "line: '${seq}'\n";
}
./808927.pl syntax OK