use strict;
my $str = 'a
b
BEGIN
c
d
e
END
f
g
h
i
j
BEGIN
k
l
m
n
o
p
q
END
r
s
t
u
v
BEGIN
w
x
y
END
z';
my $regex = qr/(\bBEGIN\b([\w\n]*?)\bEND\b\n)/p;
my $subst = '';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html