$re = '/(?x) # invoke extended (aka free-spacing) mode
^ # match beginning of the string
[^"\n]* # match zero or more chars other than line terminators and double-quotes
" # match a double-quote
[^"\n]* # match zero or more chars other than line terminators and double-quotes
[^ "\n] # match a character other than a space, double-quote or newline
" # match a double-quote
\n # match a newline
\ * # match zero or more spaces
" # match double-quote
[^ "\n] # match a character other than a space, double-quote or newline
[^"\n]* # match zero or more chars other than line terminators and double-quotes
" # match a double-quote
\n? # optionally match a newline
$ # match end of string/m';
$str = 'abc def "ghi jkl\\n"
"mno pqr"';
preg_match_all($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