my $last_match;
if ( grep { /^tag\: (.*)$/ and $last_match = $1 and 1} <FILE> ) {
        print "Found tag: $last_match\n";
}

##</code><code>##

while (<FILE>) {
   next unless /^tag\: (.*)$/;
   print "Found tag: $1\n";
}

##</code><code>##

print map /^tag\: (.*)$/ ? "Found tag: $1\n" : (), <FILE>;