I'm not exactly sure what it is that you have been wanting to perform with your code, but why aren't you using perlfunc:sprintf ? This would simplify your code greatly. eg.

my $som_rekening = "2147483648";
my $padded_som = sprintf("%15d", $som_rekening);
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This is where I'm not sure what you are wanting to achieve with the last line? Maybe you could paste a little more of your code outlining what it is you are wanting to achieve?

 

Update : - If its the numeric accuracy of Perl that you running up against as davorg suggests, then I would most certainly concur with his decision to look at Math::BigInt

 

perl -e 's&&rob@cowsnet.com.au&&&split/[@.]/&&s&.com.&_&&&print'