#!/usr/bin/perl
use strict;
use warnings;


while (my $line = <DATA>)
{
   process_record($line) if $line =~ /START/;
}

sub process_record
{
   my ($line) = @_;
   my @lines;
   my $found;
   
   push @lines, $line; #the "START" line
   
   while ( $line = <DATA>, $line !~ /END/)
   {
     $found = 1 if $line =~ /def/;
     push @lines, $line;
   }
   push @lines, $line;  #the "END" line
   
   print @lines unless $found;
   return;
}

=prints
    START
xyz
abc
    END
=cut

__DATA__
    START
abc
def
ghi
    END
junk
more junk
    START
xyz
abc
    END