| stands for "or" only inside a regular expression. Outside, you have to use || or or. The vertical bar alone is a "bitwise or", see perlop. No "or" is needed, though:

#!/usr/bin/perl
use warnings;
use strict;

use Test::More;
my $r = qr/^-?           # Can start with a minus.
            (:?          # Non capturing group.
               [0-9]+    # Digits. Does not match Unicode digits as \d
+ does.
               (?:       # Another group, this one will be optional.
                  \.     # The dot. Backslashed to lose its special me
+aning.
                  [0-9]+ # Digits again.
               )?        # End of the inner group, the ? makes it opti
+onal.
            )            # End of the outer group.
            $            # And nothing more.
            /x;

like  ($_, $r) for qw/ 4   -7 0.656 -67.35555 /;
unlike($_, $r) for qw/ 5. 56F   .32      -.04 /;

done_testing();
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