I would like to get everything between two stars - except of they have a leading backslash.

So for example:

```
*hello* world

```

should return "hello", but

```
*hello \* world*

```

should return "hello \* world"

I tried the following regex:

```
/(?<!\\)\*(.+?)(?<!\\)\*/s

```

which works perfect on <http://regex101.com/> but php returns:

> 
> Warning: preg\_replace(): Compilation failed: missing ) at offset 21
> 
> 
> 

What am I doing wrong?

--

EDIT 1:
Here's my PHP-Code for that:

```
var_dump(preg_replace('/(?<!\\)\*(.+?)(?<!\\)\*/s', '<strong>$1</strong>', '*hello world*'));

```