sub binary2decimal
{
  defined $_[0] or return 0;
  my $B = $_[0];

  $B =~ tr|01||cd;                          # Remove illegal chars
  $B =~ s/^0+//;                            # Remove preceding zeros
  my @BITS = split(//, $B);

  my $n = 0;
  my $copy1;
  my $copy2;
  my $copy3;

  foreach (@BITS)
  {
    $copy1 = $n;
    $copy2 = $n;
    $copy1 =~ tr/1-9/246802468/;
    $copy2 =~ tr/1-9/00001/;
    $n = (0 . $copy1 || $copy2 . $_);   # This should be | not ||
    $n =~ s/^0+(?=.)//;
  }
  return $n;
}
[download]

Not my code, and far too tricky to maintain in my opinion.

Relying on the idiosyncracies of | is nothing I recommend.

I even have problems to reproduce my own explanation in the debugger.

The original code works tho when tested. 🤷🏻‍♀️

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}

> I even have problems to reproduce my own explanation in the debugger.

And the reason is that it's supposed to be a "bitstring" not "numeric bit" operation.

see https://perldoc.perl.org/perlop#Bitwise-String-Operators

hence replacing | with |. under use feature "bitwise" will stop doing hard to predict things, even after refactoring this golfing code.

ugh...

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}