#!/bin/sh

perl -i~ -e '  # -i~ for in-place editing with tilde backup
  use strict;
  use warnings;
  my @a;
  my %excludehash;
  my $file = shift;
  open(excludelist, "< $file") or die;
  chomp( @a=<excludelist> );
  close(excludelist);
  @excludehash{@a}=@a;
  {
    local($/) = "";
    while (<>) {
      m/YOURKEY:\s+(.*)$/m;
      print unless exists $excludehash{ $1 }
    }
  }' "excludefile" "datafile"