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<?php $a = 'Ukraine - Russia or Iran - Argentina'; preg_match('/([ ]*[-]?[ ]*){1}(or){1}/', $a, $m, PREG_OFFSET_CAPTURE); var_dump($m);
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
array(3) { [0]=> array(2) { [0]=> string(3) " or" [1]=> int(16) } [1]=> array(2) { [0]=> string(1) " " [1]=> int(16) } [2]=> array(2) { [0]=> string(2) "or" [1]=> int(17) } }

preferences:
310.96 ms | 406 KiB | 460 Q