use Tie::File;
sub vpenv {
  my $file = shift;
  tie my @stuff, 'Tie::File', $file or die "Unable to tie $file: $!";
  $stuff[0]="setenv DSCUSTOMER $db\n";
  $stuff[1]="setenv DSSITENO $sno\n";
  $stuff[2]="setenv DSCUSTID $sid\n";
  untie @stuff;
} 

sub vpdb {
  my $file = shift;
  tie my @thing, 'Tie::File', $file or die "Unable to tie $file: $!";
  $thing[0]=".ARG DATABASE $db\n";
  untie @thing;
}

vpenv("$location/$dir/$site/$vpfile");
vpdb("$location/$dir/$site/$vpdir/$vpdata");