Just to provide another way:

my $string = "calendarview.pl?loginid=102138&month=04&year=2003&studen
+t_id=&user_type=TUTOR&CalendarName=102138Academic&framename=top.index
+_main&session_number=618280744437303";
my $i = index($string,"CalendarName=") + length("CalendarName=");
my $j = index($string, "&", $i);
substr($string,$i,$j-$i) = "";
[download]

I don't recommend it, but I'm always astounded that this is possible, maybe one enlightened monk can come up with a suggestion where this lvalue-assignement (?!?) is useful.
Update: in Re: Replace zero-width grouping?, BrowserUk comes up with a good use of an substr lvalue--assignement.

regards,
tomte

Hlade's Law:

If you have a difficult task, give it to a lazy person --
they will find an easier way to do it.