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<?php $array = [ 'FILE-F01-E1-S01.pdf', 'FILE-F01-E1-S02.pdf', 'FILE-F01-E1-S03.pdf', 'FILE-F01-E1-S04.pdf', 'FILE-F01-E1-S05.pdf', 'FILE-F02-E1-S01.pdf', 'FILE-F02-E1-S02.pdf', 'FILE-F02-E1-S03.pdf', "TESTFILE-F01-E1-S03.pdf" ]; $parts = explode('-', $array[0]); array_pop($parts); $fileBeginning = implode('-', $parts); $secondArray = array_filter($array, function ($x) use ($fileBeginning) { return substr($x, 0, strlen($fileBeginning)) === $fileBeginning; }); print_r($secondArray);

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