preg_replace转义<？ 和？>

Question

I want to remove the first occurrence of <? and the last occurrence of ?> from a string using preg_replace, but no matter how I attempt to escape them, they always cause trouble.

PHP Code

$string = preg_replace('/<?/', '', $string);
$string = preg_replace('/?>/', '', $string);

What shall I write into the expression area?

Answer 1

You can use:

$string = preg_replace('/^((?:(?!<\?).)*)<\?|\?>(?!.*?\?>)/s', '$1', $string);

RegEx Demo

Or quite simply:

$string = preg_replace('/<\?(.*)\?>/s', '$1', $string);

PS: Note that you can do this without using regex also. Use strpos and strrpos functions in PHP to get first position of <? and last position of ?> and then use substr function.