<?php
$dannie = "Длина: 100 м
Длина 100 метров
Длина 100м";
if (preg_match_all('~Длина:\s*\K\d+(?:[.,]\d+)?~u', $dannie, $matches)) {
echo implode(', ', $matches[0]);
}
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
100