- preg_match: documentation ( source)
<?php
$artigos = [
"Art. 1 lala 23",
"Art. 2 lala 23",
"Art. 3 lala 23",
"Art. 4345 lala 23",
];
$artigos_len = count($artigos) -1;
for ($i=0; $i <= $artigos_len; $i++) {
$tmp_num = preg_match("/Art\. (\d)+/i",$artigos[$i],$match);
echo "Numero de Artigo: ".$match[0];
}