A regex will parse the file just fine. Just grab the whole file into a variable, then do this:

#Sample data, multiline
$line = "<!-- Begin -->Line one\nLine two\nthree\nfour<!-- End -->";

#process them
$line =~ s/<!-- Begin -->(.*)<!-- End -->/$1/s;
print $line;
[download]

I tried to do the same while reading the file line-by-line... The code was so ugly that I simply recommend to read in the whole file at once and do a multiline regexp above...

HTH