my $str =
  q{[S [NP This NP] [VP is [NP [PP to [NP the left NP] PP] NP] VP] . S
+]};

my $bracket;

$bracket = qr{
  (?:
    (?> [^][]* )
    |
    \[ (??{ $bracket }) \]
  )+
}x;


for (get_brackets($str, 1)) { print "<$_>\n" }
for (get_brackets($str, 2)) { print "<<$_>>\n" }


sub get_brackets {
  my ($str, $depth) = @_;
  my @hits = $str;
  @hits = map m{\[($bracket)\]}g, @hits
    for 1 .. $depth;
  return map "[$_]", @hits;  # put the []'s back in
}
[download]

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

Have a look at Text::Balanced.

Greetings Dr.Altaica,

You have an interesting situation. I'm sure there must be a module out there that does nearly exactly what you want, but since you specifically asked for something that will work "only in the standared distubution of Perl," here's my code:

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

my $input = '[S [NP This NP] [VP is [NP [NP the turning point NP] ' . 
    '[PP to [NP the left NP] PP] NP] VP] . S]';

$input =~ s/^\[S\s*(.*?)\s*S\]$/$1/;

my $bracket_count = 0;
my @output;
my $build_var;

foreach (split(//, $input)) {
    $build_var .= $_;

    if (/\[/) {
        $bracket_count++;
    } elsif (/\]/) {
        $bracket_count--;
    }

    if ($bracket_count == 0) {
        push @output, $build_var if ($build_var ne ' ');
        $build_var = '';
    }
}

foreach (@output) {
    print '"', $_, '"', "\n";
}
[download]

It's not fancy or nice, and probably will need to be patched a bit for situations that fall outside of your given example. However, it does seem to return the results that you want.

-gryphon
code('Perl') || die;

Just in case, test to see whether $bracket_count ever goes to -1. In the case where your string is aaa]bbb[... you probably want to do something a little more drastic than pushing (a, a, a, ]bbb[) into the output array :)

Thanks gryphon, not exactly what [I wanted] but that was my was'nt clear about what I wantd. I should have used an example like: '[VP This stuff is [NP the left NP] [NP other thing NP] VP]' into ("This stuff is", "[NP the left NP]", "[NP other thing NP]") Here's the code that works like a need incase someone else need to split a anchor deliminated strings(in this case the center of " [" and "] ")and ignore the nested ones.nested

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

#my $input = '[VP is [NP one NP] it [NP two NP] working VP]';
my $input = '[VP This stuff is [NP the left NP] [NP other thing NP] VP
+]';
#my $input = '[VP [NP This NP] [VP is [NP [NP the turning point NP] [P
+P to [NP the left NP] PP] NP] VP] . VP]';
#my $input = '[S [NP This NP] [VP is [NP [NP the turning point NP] ' .
+ 
#        '[PP to [NP the left NP] PP] NP] VP] . S]';

$input =~ s/^\[\w+\s*(.*?)\s*\w+\]$/$1\n/;

my $bracket_count = 0;
my @output;
my $build_var;

foreach (split(//, $input)) {

        if (/\[/) {
                if ($bracket_count == 0) {#DR
                        $build_var =~ s/^\s*|\s*$//g;#dr
                        push @output, $build_var if ($build_var ne '')
+;#DR
                        $build_var = '';#DR
                }#DR
                $bracket_count++;
                $build_var .= $_;#dr
        } elsif (/\]/) {
                $bracket_count--;
                $build_var .= $_;#dr
                if ($bracket_count == 0) {#DR
                        $build_var =~ s/^\s*|\s*$//g;#dr
                        push @output, $build_var if ($build_var ne '')
+;#DR
                        $build_var = '';#DR
                }#DR
        } elsif (/\n/) {#dr Should be the end
                $build_var =~ s/^\s*|\s*$//g;#dr
                push @output, $build_var if ($build_var ne '');#DR
        } else {#dr
                $build_var .= $_;#dr
        }

}

foreach (@output) {
        print '"', $_, '"', "\n";
}
[download]

sub split_delimited {
    my $input = shift;
    my $limit = shift;
    my @output;
    my $s = '';
    my $t = '';
    my $bracket_count = 0;
    my $build_var;

    $input =~ s/\n/ /gm;
    foreach ( split ( //, $input ) ) {
        $build_var .= $_;
        if (/\{/) {
            $bracket_count++;
        }
        elsif (/}/) {
            $bracket_count--;
        }
        elsif ( / / and $bracket_count == 0 ) {
            push @output, $build_var if ( $build_var and $build_var ne
+ ' ' );
            $build_var = '';
        }
    }
    foreach  (@output) {
        if (length($s) < $limit) {
            $s .= $_;
        }
        else {
            $t .= $_;
        }
    }
    return $s,$t;
}
[download]

This returns two substrings without violating any of the formatting within the parent string, but still solving whatever problems being over the 'limit' would cause.

As was pointed out, there are a number of module approaches to this problem, but given the constraint you mentioned, I wouldn't hesitate to use this code— In fact I did, thanks gryphon!

BTW, your example is delimited, but I think I know what you meant…

$_ = '[S [NP This NP] [VP is [NP [NP the turning point NP] [PP to [NP 
+the left NP] PP] NP] VP] . S]';
#$_ = '[VP This stuff is [NP the left NP] [NP other thing NP] VP]';
@( = ('(','');
@) = (')','');
($re=$_)=~s/((\[\w+\s*)|(\s*\w+\])|.)/$)[!$3]\Q$1\E$([!$2]/gs;
$re = join'|',map{quotemeta}eval{/$re/};
die $@ if $@=~/unmatched/;
$_ = (eval{/($re)/})[0];
print join"\n\n",/\s*(\[\w+\s*(?:$re)\s*\w+\]|[^][]*)/g,"";
[download]