I know how to find a (part of a) string and change that, but the problem is, the part I have to change is variable in length and in characters.

example

```
$string = "bla1bla2bla3textbla4bla5";

```

normaly I should explode to filter out text, but because "bla3" is different to "bla4", I have no idea how to explode or find "text", however it's always between "bla3" and "bla4", but "text" is variable aswel as bla1, 2 and 5.
after I find "text" I need to replace it by an other text.

Perhaps I can find this on google, but the problem is, I have no clue how to discribe it.