$ php -v PHP 8.2.7 (cli) (built: Jun 9 2023 19:37:27) (NTS) $ php -r 'var_dump(preg_match("/^[a-z0-9 ]+\$/", "hello world"));' int(1) $ php -r

$ php -v PHP 8.2.7 (cli) (built: Jun 9 2023 19:37:27) (NTS) $ php -r 'var_dump(preg_match("/^[a-z0-9 ]+\$/", "hello world"));' int(1) $ php -r 'var_dump(preg_match("/^[a-z0-9 ]+\$/", "hello\nworld"));' int(0) $ php -r 'var_dump("hello\nworld");' string(11) "hello world" ... $ php -v PHP 7.2.26-1+0~20191218.33+debian8~1.gbpb5a34b (cli) (built: Dec 18 2019 16:09:52) ( NTS ) $ php -r 'var_dump(preg_match("/^[a-z0-9 ]+\$/", "hello world"));' int(1) $ php -r 'var_dump(preg_match("/^[a-z0-9 ]+\$/", "hello\nworld"));' int(0) $ php -r 'var_dump("hello\nworld");' string(11) "hello world" I'm not sure which version of PHP had the behavior you describe, or whether it misbehaves under more specific conditions, but preg_match() is one of the more commonly-used regex functions, all of which share the same engine. The behavior here seems to be "correct" for at least the last 5 years, for varying interpretations of "correct". edit: https://3v4l.org/N4o8D https://3v4l.org/N4o8D suggests that the behavior here is identical for all versions of PHP from 4.3 to 8.3.6.