Question

I am using the preg_split function in PHP in order to create one array containing several different elements. However, I want to exclude a string which happens to contain one of the elements that I’m preg_splitting by.

$array['stuff'] = preg_split('/\[#]|\ &amp  |\ &amp |\&amp |\&amp|\ &amp|\ &gt  |\ &gt |\&gt |\&gt|\ &gt|\ &  |\ & |\& |\&|\ &|\ \/  |\ \/ |\\/ |\\/|\ \/|\ >  |\ > |\> |\>|\ >|\ ,  |\ , |\, |\,|\, |\ ::  |\ :: |\:: |\ ::|\::|\ ::|\ :  |\ : |\: |\:|\ :|\ -  |\ - |\- |\-|\ -/', $array['stuff'] ) ;

What I would like to do is to exclude a string such as ‘foo-bar’ from being matched for a split because it contains a dash. ‘foo-bar’ would need to be an exact match for my purposes.

Answer 1

The resulting regular expression would be very complicated specially if you have a lot exceptions like ‘foo-bar’.

You should use a conditional subpattern with a lookbehind as condition and a lookahead as its yes-pattern:

$res = preg_split('/(?(?<=foo)\-(?!bar)|\-)/', 'aasdf-fafsdf-foo-bar-asdf' );
var_dump( $res );

result:

array(4) {
  [0]=>
  string(5) "aasdf"
  [1]=>
  string(6) "fafsdf"
  [2]=>
  string(7) "foo-bar"
  [3]=>
  string(4) "asdf"
}

---

Let me explain what is happening here. \- means

Match any dash character.

but what we want is

Match any dash character that is not part of foo-bar.

Since we can’t implement that in regex as it is we change it a little:

Match any dash character that if preceded by foo is not followed by bar.

To implement the if part we use a conditional subpattern, this is the syntax:

(?(condition)yes-pattern|no-pattern)

Our “condition” would be “preceded by foo” to check for that we use a lookbehind:

(?<=foo)

If that is true we should look for “a dash that is not followed by bar” to do that we use a negative lookahead:

\-(?!bar)

And that becomes our “yes-pattern”. Our “no-pattern” should be \- or “any dash”. The complete regex would be:

(?(?<=foo)\-(?!bar)|\-)

---

UPDATE: to incorporate this into your current regex change this part at the end:

|\ -  |\ - |\- |\-|\ -/

to

|\s?(?(?<=foo)\-(?!bar)|\-)\s?/