For each name, the full file name of the command is determined by searching the directories in PATH and remembered.
-p: no path search is performed, and filename is used as the full file name of the command.
-r: forget all remembered locations.
-d: forget the remembered location of each name.
-t: the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname.
-l: output is displayed in a format that may be reused as input.
If no arguments are given, or if only -l is supplied, information about remembered commands is printed.