It's not entirely clear to me what you're trying to accomplish, nor to anyone else, it seems. Perhaps it's this:

use strict;
use vars qw ( %data $digit );
$data{value} = 'abcd.$digit.xyz';

sub process_value
{
    $digit = 1000;
    $data{value} = eval qq["$data{value}"];
    print "\$data{value} $data{value} \n";
}

&process_value;
[download]

Output is:

$data{value} abcd.1000.xyz
[download]