This function searches within the given DIRECTORY and its
subdirectories for the specified FILENAME, calling the function
CALLBACK for each occurrence found. CALLBACK is a function that you
provide. It takes no arguments and returns an integer value.
The callback function is called when the search enters a new subdirectory, and
when a matching file has been found.
clearwin_string@('FIND_FILE_CALLBACK_REASON') is used to distinguish between
these cases returning either 'FILE_FOUND' or 'CHECKING_DIRECTORY'.
Subsequently clearwin_string@('FILE_FOUND') returns the file name if
a file has been found whilst clearwin_string@('CHECKING_DIRECTORY')
returns the full name of a directory if the search enters a new
The callback function should return 1 to stop the search or 0 to continue.
If the search is stopped, FIND_FILE@ returns 1 whilst if it completed
successfully it returns zero.
The directory and filename strings must not exceed 260 characters.
Follow the link to find some sample code.