tcsh, not especially to my surprise, does not meet the SVID or POSIX, then.
_Unix Shell Programming_, Kochan and Wood, 1985, Hayden, p 251:
"Another Way To Pass Variables To A Subshell
If you want to send the value of a variable to a subshell, there's another
way to do it besides setting the variable and then exporting it. On the
command line, you can precede the name of the command with the assignment
of as many variables as you want. For example:
DBHOME=/unx2/data DBID=452 dbrun
places the variables DBHOME and DBID, and their indicated values, into the
environment of dbrun, and then dbrun gets executed. *These variables will
not be known to the current shell; they're created only for the execution
of dbrun.*"
(Emphasis mine).
Cheers,
-- jra