Remove newline character from a string using PHP regex
$string = str_replace(PHP_EOL, '', $string);
or
$string = str_replace(array("\n","\r"), '', $string);
$string = str_replace("\n", "", $string);
$string = str_replace("\r", "", $string);
To remove several new lines it's recommended to use a regular expression:
$my_string = trim(preg_replace('/\s\s+/', ' ', $my_string));
Better to use,
$string = str_replace(array("\n","\r\n","\r"), '', $string).
Because some line breaks remains as it is from textarea input.