Getting contents of square brackets with regex, including nested ones - php

Question

Is there any way to have this:
[one[two]][three]
And extract this with a regex?
Array (
[0] => one[two]
[1] => two
[2] => three

Answer 1

For PHP you can use recursion in regular expressions that nearly gives you what you want:
$s = 'abc [one[two]][three] def';
$matches = array();
preg_match_all('/\[(?:[^][]|(?R))*\]/', $s, $matches);
print_r($matches);
Result:
Array
(
[0] => Array
(
[0] => [one[two]]
[1] => [three]
)
)
For something more advanced than this, it's probably best not to use regular expressions.

Answer 2

You can apply the regex with a loop, for example,
Match all \[([^\]]*)\].
For each match, replace \x01 with [ and \x02 with ] and output the result.
Replace all of \[([^\]]*)\] into \x01$1\x02 (warning: assumes \x01 and \x02 are not used by the string.)
Repeat 1 until there's no match.
But I'd write a string scanner for this problem :).

Answer 3

#!/usr/bin/perl
use Data::Dumper;
#a = ();
$re = qr/\[((?:[^][]|(??{$re}))*)\](?{push#a,$^N})/;
'[one[two]][three]' =~ /$re*/;
print Dumper \#a;
# $VAR1 = [
# 'two',
# 'one[two]',
# 'three'
# ];
Not exactly what you asked for, but it's kinda doable with (ir)regular expression extensions. (Perl 5.10's (?PARNO) can replace the usage of (??{CODE}).)

Answer 4

In Perl 5.10 regex, you can use named backtracking and a recursive subroutine to do that:
#!/usr/bin/perl
$re = qr /
( # start capture buffer 1
\[ # match an opening brace
( # capture buffer 2
(?: # match one of:
(?> # don't backtrack over the inside of this group
[^\[\]]+ # one or more non braces
) # end non backtracking group
| # ... or ...
(?1) # recurse to bracket 1 and try it again
)* # 0 or more times.
) # end buffer 2
\] # match a closing brace
) # end capture buffer one
/x;
print "\n\n";
sub strip {
my ($str) = #_;
while ($str=~/$re/g) {
$match=$1; $striped=$2;
print "$striped\n";
strip($striped) if $striped=~/\[/;
return $striped;
}
}
$str="[one[two]][three][[four]five][[[six]seven]eight]";
print "start=$str\n";
while ($str=~/$re/g) {
strip($1) ;
}
Output:
start=[one[two]][three][[four]five][[[six]seven]eight]
one[two]
two
three
[four]five
four
[[six]seven]eight
[six]seven
six