use strict;
use warnings;

open my $fh, '<', 'testfile.txt' or die $!;


my $position = tell $fh;

while ( defined( my $line = <$fh> ) ) {
    print "First read:\t $line";
    seek $fh, $position, 0 or die $!;
    my $reread = <$fh>;
    print "Second read:\t $reread";
} continue {
    $position = tell $fh;
}

close $fh;