PHP, regex and multi-level curly brackets

Question

I've got a string which consists of few sentences which are in curly brackets that I want to remove. That would be not that hard to do (as I know now.), but the real trouble is it's multilevel and all I want to strip is the top level brackets and leave everything inside intact. It looks something like this:

{Super duper {extra} text.} {Which I'm really {starting to} hate!} {But I {won't give up} so {easy}!} {Especially when someone is {gonna help me}.}

I want to create an array that would consist of those four entries:

Super duper {extra} text.
Which I'm really {starting to} hate!
But I {won't give up} so {easy}!
Especially when someone is {gonna help me}.

I have tried two ways, one was preg_split which didn't do much good:

$key = preg_split('/([!?.]{1,3}\} \{)/',$key, -1, PREG_SPLIT_DELIM_CAPTURE);
$sentences = array();

for ($i=0, $n=count($key)-1; $i<$n; $i+=2) {
$sentences[] = $key[$i].$key[$i+1]."<br><br>";
}

Another one was using preg_match_all which was quite good until I realized I had those brackets multilevel:

$matches = array();
$key = preg_match_all('/\{[^}]+\}/', $key, $matches);
$key = $matches[0];

Thanks in advance! :)

@Vulcan I have added info about what I've tried to the original post. — moskalak
– moskalak, Commented Jun 13, 2012 at 23:01
Are the top-level curly brackets always separated by a single space? — nickb
– nickb, Commented Jun 13, 2012 at 23:08

Qtax · Accepted Answer · 2012-06-13 23:09:55Z

5

You can use a recursive expression like this:

/{((?:[^{}]++|(?R))*+)}/

The desired results will be in the first capturing group.

Usage, something like:

preg_match_all('/{((?:[^{}]++|(?R))*+)}/', $str, $matches);
$result = $matches[1];

edited Jun 13, 2012 at 23:09

answered Jun 13, 2012 at 22:58

Qtax

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2 Comments

moskalak Over a year ago

Edit: It works and I get it, thank you very much, sir! Now I only need to understand what exactly this regexp does. :)

Qtax Over a year ago

@moskalak, the elements in $matches[1]. Also welcome to SO, here best way to thank is by up voting. ;-)

ghoti · Accepted Answer · 2012-06-13 23:01:15Z

4

$x="foo {bar {baz}} whee";
$re="/(^[^{]*){(.*)}([^}]*)$/";
print preg_replace($re, "\\1\\2\\3", $x) . "\n";'

returns:

foo bar {baz} whee

answered Jun 13, 2012 at 23:01

ghoti

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1 Comment

moskalak Over a year ago

Thank you for this proposition. It would be great, but it returns a string stripped of top-level brackets while I really need to create an array in which every string bracketed at top-level would be another entry.

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