To do this in the fewest lines I would suggest using the built-in DIRECTORY_SEPARATOR
constant along with explode(delimiter, string)
to separate the path into parts and then simply pluck off the last element in the provided array.
Example:
$path = 'F:\Program Files\SSH Communications Security\SSH SecureShell\Output.map'
//Get filename from path
$pathArr = explode(DIRECTORY_SEPARATOR, $path);
$filename = end($pathArr);
echo $filename;
>> 'Output.map'