$ perl -le'print join " : ", split /(\|)/, "2|3|||||"'
2 : | : 3 : | :  : | :  : | :  : | :  : |
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$ perl -le'print join " : ", grep ++$i%2, split /(\|)/, "2|3|||||"'
2 : 3 : : : :
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Update: Yikes! I caught a mistake: the last field still disappears if empty. Count the pipes in the string and the colons in the output.. At this point we lose some grace.. The oneliner is ugly:

$ perl -le'print(join(" : ", grep(++$i%2, split /(\|)/, "2|3|||||"), (
+"")x(1-$i%2)))'
2 : 3 : : : : :
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$ perl -le'my @field = grep ++$i%2, split /(\|)/, "2|3|||||"; push @fi
+eld, "" unless $i%2; print @field'
2 : 3 : : : : :
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Makeshifts last the longest.

That is damn elegant.

UPDATE: After reading your update, i was a little dissapointed that i wouldn't be able to use your clean little trick, untill I looked at my data some more. Unlike ever other "seperated" data format I've ever seen, it allways puts a trailing seperator after the last field -- which means your orriginal one liner will work perfect for me ...I need to ignore the last pipe

go figure

You know, that gives me another idea for the cases you need to conserve the last field, although it is so similar to the add a bogus field approach that it bears the question whether the capture/grep hoopla is worth the hassle if you went that route anyway: add a field separator to the string.

$ perl -le'$_ = "2|3|||||"; print join " : ", grep ++$i%2, split /(\|)
+/, "$_|"'
2 : 3 :  :  :  :  :
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Makeshifts last the longest.

If LIMIT is specified and positive, splits into no more than that many fields (though it may split into fewer). If LIMIT is unspecified or zero, trailing null fields are stripped (which potential users of "pop" would do well to remember). If LIMIT is negative, it is treated as if an arbitrarily large LIMIT had been specified.

An example (with quoting changes so it will work on Win2K),

C:\>perl -Mstrict -Mwarnings -le "print 'defined!' if defined( (split 
+/\|/, '2|3|||||', -1)[4]);"
defined!
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hth...

After all of the bugs, updates, and general messiness caused by this question, I started wondering if using split was really the right way to go. It can be done with a regex:

my @tests = ( '', qw(
    2|3|||||
    2
    2|
    2|3
    2|3|
    |
    |2
    |2|
    |2|3
    |2|3|
));


for my $string (@tests) {

    # Splits on '|' and preserves empty fields...
    my @fields = $string =~ m/((?:^|(?<=\|))[^|]*)/g;

    printf "%-10s :", "'$string'";
    print "($_)" for @fields;
    print "\n";
}
__END__
''         :()
'2|3|||||' :(2)(3)()()()()()
'2'        :(2)
'2|'       :(2)()
'2|3'      :(2)(3)
'2|3|'     :(2)(3)()
'|'        :()()
'|2'       :()(2)
'|2|'      :()(2)()
'|2|3'     :()(2)(3)
'|2|3|'    :()(2)(3)()
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However, constructing that regex wasn't particularly easy. I think, had I been faced with this task myself, I would have opted for the method you suggested. That is, append a non-empty field and then pop it off of the array after you split. At first it seems kind of a dirty trick but once you find how difficult it is to do it otherwise,

    my @fields = split /\|/, $string.'|x'; pop @fields;
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-sauoq
"My two cents aren't worth a dime.";

Argh... I thought I could do better, but to get your exact results, all I could come up with was:

my @fields = $string =~ m/([^|]*)\|?/g;
$string && $string !~ /\|$/ && pop @fields;
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That second line can get a bit simpler if you define an empty string to have zero fields instead of having a single null field.

Congrats, your solution is better than mine even though it looks unnecessarily complicated.

I think the best suggestion so far is to tell split how many fields you want:

my @fields = split(/\|/,$string,$string =~ tr/|/|/ + 1);
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Though I'd probably break it up into two lines:

my $fieldcount = $string =~ tr/|/|/ + 1;
my @fields     = split(/\|/, $string, $fieldcount);
[download]

-Blake