#!/usr/bin/perl
use common::sense;
my $data = join('', <DATA>);
$data =~ s{(^|\n)begin\n         # begin at start of string or line
          (.*?\n)*?              # lines to skip (non-greedy)
          end\n}                 # matching end
         {$1begin\nend\n}sx;
print $data;
__DATA__
a
begin
1
a
2
end
c
begin
c
end
a
begin
1