How to detect if a string has a new line break in it?

line break is \r\n on windows and on UNIX machines it is \n. so its search for PHP_EOL instead of "\n" for cross-OS compatibility, or search for both "\r\n" and "\n".

Your existing test doesn't work because you don't use double-quotes around your line break character ('\n'). Change it to:

if(strstr($string, "\n")) {

Or, if you want cross-operating system compatibility:

if(strstr($string, PHP_EOL)) {

Also note that strpos will return 0 and your statement will evaluate to FALSE if the first character is \n, so strstr is a better choice. Alternatively you could change the strpos usage to:

if(strpos($string, "\n") !== FALSE) {
  echo 'New line break found';
}
else {
  echo 'not found';
}