perl -MO=Deparse

my $number = '..2314-1234123.';
if ($number =~ /\d/ * /^([\d.-]+)$/) {
    print "$1\n";
}
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The original trick is multiplying the first regex result (as a scalar) by the second regex result (as a scalar). That is, 1*1 is true, but 0*1 is false.

However, since the two regexen aren't being bound to $number in your example, the code actually doesn't work. The second regex is searching $_ for matches instead.