See the UNIX Programmers Manual or via % man csh
% which script
will display which executable is used for the command 'script', i.e.:
/usr/ucb/script
This command (presumably) reads the hash table which is generated at login
time (or as the result of a 'rehash' command) in order to determine where
a given executable will be fetched from. This is useful when there
is some question about WHICH executable is being used. Since this is not
always clear (due to pathnames being different from user to user),
the 'which' command will point to the appropriate executable.
NOTE: This command does NOT know about aliases.