flyingmoose,
This won't work for the reason I described above. If $increment is undefined looks_like_number will still return true.

#!/usr/bin/perl
use strict;
use warnings;
use Scalar::Util 1.10 'looks_like_number';

my $total = 4;
my $increment;

$total += looks_like_number($increment) ? $increment : 0
__END__
Use of uninitialized value in addition (+) at blah.pl line 9.
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Cheers - L~R