You haven't given us much to go on, but I'm guessing that you have some kind of serialized filename (a dataset name perhaps?), and you want to produce the next filename in the series. In such a case, the following approach would work for you:

use strict;

my $oldfile = '0001';
my $newfile = sprintf("%4.4d", $oldfile + 1);

print "New filename = $newfile\n";
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