That funny syntax represents the index of the last element of an array starting from 0, eg:

#!/usr/bin/perl

use warnings;
use strict;

my @a = qw(0 1 2 3 4 5);

print "$#a\n\n";

for my $i (0 .. $#a){
    print "$i\n";
}

print "elem 5: $a[$#a]\n"; # same as $a[-1] or $a[5]
[download]

Output:

5

0
1
2
3
4
5
elem 5: 5
[download]

-stevieb

Slight nit, even if it is not recommended use (deprecated since 5.12.0):

That funny syntax represents the index of the last element of an array starting from 0$[

Today 0 is accurate, but who knows the original context of the provided code.

--MidLifeXis

$#kbin gives the index of the last entry of array @kbin. Since @kbin is undefined, it is empty, and so the result is -1. 0 would be the first index of an non empty array.

If you use $#{$kbin}, you should get the index of the last entry of @{$kbin}, that is the array dereferenced by $kbin.

On the same lines if last-index-of-array variable, $#x, is assigned -1, array becomes empty (mentioned in perldata) ...

  DB<1> @x = ( 1 , 2 )

  DB<2> x @x
0  1
1  2
  DB<3> $#x = -1

  DB<4> x @x
  empty array
  DB<5>
[download]

Thank you for answering can you explain why $kbin = split( is used and not @kbin = split(

That's probably just a mistake. Calling split in scalar context will assign the number of items produced by the split to the scalar, so $kbin will contain the number of items the split returns, not the items themselves. That might make sense in some cases, but not here, since $kbin is being used as if it's an array later.

My first guess would be that this was written by a PHP programmer, since their arrays don't use a different sigil like Perl's do.

Aaron B.
Available for small or large Perl jobs and *nix system administration; see my home node.

The documentation explains it: perldata ... search for $#

Let see what all explain it [perldoc://"$#"] "$#" -> perlref   $aref->$#*; # same as $#{ $aref }

Wow, what a horrible search engine, that it five pages of results

 [ddg://"$#" site:perldoc.perl.org] "$#" site:perldoc.perl.org -> more of same nonsense, wow

hello http://grep.cpan.me/?q=\%24%23\w%2B+dist%3Aperl+ ->

The Perl equivalent for this is C<$#myarray>.

Set the highest index in the array to the given number, equivalent to
Perl's C<$#array = $fill;>.

RJ
[download]

hello http://grep.cpan.me/?q=\%24%23\w%2B%20dist%3Aperl%20+dist=perl

trigger for I<container magics>, i.e. it will for C<%ENV> or C<%SIG>
but not for C<$#array>.

perl-5.22.0/pod/perldata.pod

    $days{'Feb'}    # the 'Feb' value from hash %days
    $#days        # the last index of array @days

The length of an array is a scalar value.  You may find the length
of array @days by evaluating C<$#days>, as in B<csh>.  However, this
isn't the length of the array; it's the subscript of the last elemen

which is a different value since there is ordinarily a 0th element.
Assigning to C<$#days> actually changes the length of the array.
Shortening an array this way destroys intervening values
[download]

hello http://search.cpan.org/grep?cpanid=RJBS&release=perl-5.22.0&string=\%24%23&i=1&n=1&C=0#pod/perldata.pod

pod/perldata.pod

53:    $#days           # the last index of array @days
357:of array @days by evaluating C<$#days>, as in B<csh>.  However, th
+is
360:Assigning to C<$#days> actually changes the length of the array.
364:X<$#> X<array, length>
373:    $#whatever = -1;
382:    scalar(@whatever) == $#whatever + 1;
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Or one could, as toolic suggests, actually look at perldata and search for the string '$#', which yields

The length of an array is a scalar value. You may find the length of
array @days by evaluating $#days, as in csh. However, this isn't the
length of the array; it's the subscript of the last element ...

as the second hit, followed by a few more informative paragraphs.

---

Give a man a fish:  <%-(-(-(-<

...
  PPI::Token::ArrayIndex  '$#kbin'
...