brewkit.rb changes ENV destructively, so lets not do that everytime a formula
is required. Now it's possible for other tools to require a formula
description without worrying about side-effects.
The PCRE library is a set of functions that implement regular expression
pattern matching using the same syntax and semantics as Perl 5. PCRE has its
own native API, as well as a set of wrapper functions that correspond to the
POSIX regular expression API. The PCRE library is free, even for building
commercial software.
