I was looking at this and thought, hey it can't be too hard...after some non-trivial effort, I whipped out Jeffrey Friedl's book, "Mastering Regular Expressions".

In Chapter 5, page 194, he says: "on the vast majority of systems, you simply can't match arbitrarily nested constructs with regular expressions." There are ways in Perl to do some zoomy things like dynamically create a regex at some depth. But my investigation appears to indicate that this is NOT "just a split" and that figuring out that something like [e, [f, g, h, [i, j], k, l], m, n] is all one thing, is likely to be darn difficult in a single regex, if we assume that we just don't know how deep the nesting levels of [ ] go!

There is a posting with some code that counts left and right brackets to figure out the depth. Do NOT assume that more lines is slower! Something is weird in my browser now and I can't look again at that code easily at the moment, but I suspect that it is likely to be (or something very similar to it) to be the fastest thing going. Either that or this "balanced" module that was also suggested.

I'm just saying that if J. Friedl says this problem is hard, I'm unlikely at my skill level to arrive at a "simple" solution that proves him wrong.

here is my effort at some code - I can't do it with one regex:

#!/usr/bin/perl -w
use strict;

my $test="xyz,[a,b],c,'d',[e,[f,g,h,[i,j],k,l],m,n],o,p";

my @test = $test =~ m/,|[\w']+|[\[\]]/g;
my @result;
while (@test)
{
   my $t = shift @test;
   if ($t =~ /[\w']+/) { push (@result, $t); } #simple "word" thing
   elsif ($t =~ /\[/)              #complex bracketed expression
   { 
      push (@result, bracket_exp());
   }
   # commas are skipped..
}

sub bracket_exp
{
   my $temp ="[";
   my $depth = 1;
   while ($depth)
   {
     my $next_thing = shift @test;
     $temp .= $next_thing;  
     $depth++ if $next_thing eq '[';
     $depth-- if $next_thing eq ']';
   }
   return ($temp);
}

foreach my $t ( @result)
{
   print "$t\n";
}

__END__
prints:
xyz
[a,b]
c
'd'
[e,[f,g,h,[i,j],k,l],m,n]
o
p
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.