"You could stick spaces into those 'empty' bars by swapping with something like this: while($line =~ s/\|\|/\| \|/){}"

Perhaps I'm missing your intent, but that seems like an unnecessarily complicated way to get a repeat substitution when the 'g' modifier is provided for that task:

$ perl -Mstrict -Mwarnings -E '
    my $x = q{1|2|3|||6|7||||};

    {                          
        my $line = $x;
        while($line =~ s/\|\|/\| \|/){}
        say $line;
    }                     
                                           
    {     
        my $line = $x;
        $line =~ s/\|(?=\|)/| /g;
        say $line;
    }    
'
1|2|3| | |6|7| | | |
1|2|3| | |6|7| | | |
[download]

Using the while loop instead of the 'g' modifier is also slower:

$ perl -Mstrict -Mwarnings -E '
    use Benchmark qw{cmpthese};

    my $x = q{1|2|3|||6|7||||};

    cmpthese(1e6 => {
        while_no_repeat => sub {
            my $line = $x;
            while($line =~ s/\|\|/\| \|/){}
        },
        just_repeat => sub {
            my $line = $x;
            $line =~ s/\|(?=\|)/| /g;
        }
    });
'
                    Rate while_no_repeat     just_repeat
while_no_repeat 158479/s              --            -21%
just_repeat     201613/s             27%              --
[download]

[Aside: the pipe (|) character is not special in the "replacement" part of s/pattern/replacement/ so there's no need to escape it.]

Fair point, thanks for comparing them!

Michael

But your program will miss the last empty field. In 1|2||3|45|||6|, for example, your program stops too early:

.
.
NEW: 45
NEW:
NEW:
NEW: 6
[download]

(One empty NEW: line should follow, since separators separate fields, rather than terminate them.)

If that were the only issue, you could just append a single '|' to the input string before the rest of your logic.

The second problem, though, is that your regex converts empty fields to a single space ' '. True, you could easily replace them, but if the field was ' ' in the first place, the value will be destroyed. That may not be a problem depending on the data, but to fix this, and the previous issue, you can make a couple of changes:

$line =~ s!\|!\| !g;
.
.
@new = map { substr $_, 1 } split /\|/, $line;
[download]

Or, as the OP suggested he was trying to avoid, he could just add a non-blank field to the end. In that case the entire code reduces to:

my @new = split /\|/, $line . '|sentinel';
$#new--; # Remove sentinel
[download]

But of course, split /\|/, $line, -1; still gets my vote. :-)

Two good points, thanks for pointing those out!

Michael