<?php
$text = "11
a
b
13
begin
t
899
y
50
f
end
91
h";
var_export(preg_match_all('~(?:begin|\G(?!^))(?:.(?!end))*?\K\d+~', $text, $out) ? $out : 'no matches');
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
'no matches'