this calls for a regex or two. Something like this should do nicely:

open LOG, "<$logfile" or die "Blerch: $!\n";
while (<LOG>) {
  if (/string-in-the-middle/) {print "<FONT>$_</FONT>";}
  if (/^string-at-the-beginning/) {print "<SOME_OTHER_FONT>$_</SOME_OT
+HER_FONT>";}
}
[download]

If you want the non-matching lines as well, you'll have to dress this up a bit more.

CU
Robartes-