Run this:

use strict;
use warnings;

my $perl_file = WHATEVER_VALUE_THIS_IS_SUPPOSED_TO_BE;
my $Datafile = `Datascript -p=$perl_file`;

print "Datafile = $Datafile\n";
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Is $Datafile what you expect? That is, is it the name of the file you expect to open?

EDIT: Added $perl_file = line.