Question

The text is like this:

$string = "  <L UXUHSXUS>importantText</L>";

I would like to use the lookbehind feature in PHP Regular Expression
but it generates an error everytime I try to put .+ or any regular expression things

preg_match_all('%(?<=<L.+>)([\s\S]*?)(?=</LF>)%',$string, $matches);

this gives an error.

what should I do to add .+ or .* or any reserved regular expression things in lookbehind and lookahead?

Answer 1

Since you only use positive lookarounds you could probably replace all lookarounds with non-capturing groups (?:) instead:

(?:<L.+>)([\s\S]*?)(?:</LF>)

Note that you might want to make the first search non-greedy:

(?:<L.+?>)([\s\S]*?)(?:</LF>)