The function FILESPEC()

The function FILESPEC called with the parameter D (for Drive) returns all chars up to the first colon in the filename.
Example:

 
/*                            */
  say filespec( "D", "__D__:\test" )

/* -> returns:                */
/*      "__D__:"              */

  say filespec( "D", "  D:\test" )

/* -> returns:                */
/*      "  D:"                */

In general, the function FILESPEC only checks the syntax of the parameter string; it does not check if the parameter is a valid file or directory name. (see also Expand the function FILESPEC)