$re = '/^([a-zA-Z]+?)([-\s\'][a-zA-Z]+)*?$/m';
$str = '
#should only start with alphabets
John
1John
-John
John
\\John
#Can contain spaces,- and \' but should not repeat consecutively, also there should be alphabets before and after allowed special chars
John Doe
John-Doe
John\'s Doe
John--Doe
John Doe
John\' s
John-Doe-
#Other special chars not allowed
John#Doe
J0hn
JON3
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php