Expressions

The csh supports a very flexible expression syntax for use with
conditional and loop statements.  These expressions resemble C
language expressions.  Some operators of note:

==	Equality		## Be very careful
=	Assignment		## with these two!
!=	Not Equal
=~	String matches a pattern
&&	Logical AND
||	Logical OR
!	Reverse the sense of the expression
{cmd}	1 if command succeeds, 0 otherwise; note that this reverses
	the Bourne and Korn shell meaning of "true" and "false".

-e	File exists
-r	File exists and is readable
-w	File exists and is writable
-x	File exists and is executable
-d	File exists and is a directory


