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<?php $string = "Porcupines\nare\n\n\n\nporcupiney."; echo preg_replace('~\R{1,2}~', '<br />', $string);
Output for 4.4.6 - 4.4.9, 5.2.2 - 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 - 7.2.34, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.26, 8.1.0 - 8.1.13
Porcupines<br />are<br /><br />porcupiney.
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.5, 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.1
Porcupines are porcupiney.

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