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<?php $test2 = '123_123_234_1Foo2'; preg_match_all('/(?<=^|_)\d+(?=_|$)/', $test2, $m); var_export($m[0]);
Output for 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.31, 8.3.0 - 8.3.31, 8.4.1 - 8.4.22, 8.5.0 - 8.5.7
array ( 0 => '123', 1 => '123', 2 => '234', )

preferences:
81.95 ms | 1133 KiB | 4 Q