my $LEN = 8; # Desired length
my $match;
while ($match = <STDIN>) {
    chomp $match;
    last if $LEN == length($match);
}
die "Didn't find a match" if not defined $input;
print "First match: '$match'\n";

##</code><code>##

use List::MoreUtils 'firstval';
my $match = firstval { chomp; $LEN == length } <STDIN>;