To create a regular expression for use later, we use qr//:
my $regexp = qr/^Perl$/;
This compiles the regular expression for use later. If there's a problem with your regular expression, you'll hear about it immediately. To use this pre-compiled regular expression you can use any of the following:
# See if we have a match
$string =~ $regexp;
# A simple substitution
$string =~ s/$regexp/Camel/;
# Comparing against $_
/$regexp/;