Synopsis:
   $which(<file> [<dir>[:<dir> ...]])

Technical:
   This function returns the full pathname of the specified filename.  The
   function will search the client's current LOAD_PATH for the file.  In
   addition, a list of colon-delimited directories may be specified, which
   will be searched if the file is not found in the LOAD_PATH.

Practical:
   This function tries to find the location of a particular file.  This
   makes it suitable for LOAD and STUB commands, allowing a file to be
   loaded, even if its exact location is not known.

Returns:
   the canonical path of the file, or nothing if it isn't found

Examples:
   $which(some_file)           shows full path of file
   $which(does_not_exist)      returns nothing, file dies not exist
   $which(some_file /bin)      search in /bin for some_file too

See Also:
   load(5); set(4) load_path; stub(5); which(4)