Path: utzoo!attcan!uunet!midway!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.unix.shell
Subject: Re: Help needed with conditional statement for alias in csh
Message-ID: <26553@mimsy.umd.edu>
Date: 14 Sep 90 15:24:25 GMT
References: <6929.26ed0b53@uwovax.uwo.ca> <6932.26ed237f@uwovax.uwo.ca>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 60

In article <6932.26ed237f@uwovax.uwo.ca> miller@uwovax.uwo.ca
(Greg Miller) writes:
>Followup-To: j g miller <miller@ria.ccs.uwo.ca>

(No wonder there have been no followups.  None of `j', `g', `miller', or
`<miller@ria.ccs.uwo.ca>' are valid newsgroup names....)

>if ( { test -s /usr/spool/mail/miller } ) then; echo "" ; echo "New mail" ;\
> echo "" ; endif

>If the file is present, the condition is met and the statements are
>executed.
>
>If the file is zero length, the condition is not true, then
>the sequence of commands are not executed but the if statement
>is not terminated.

Correct.

>Any ideas on why this bizarre behavior

This is the C shell we are talking about.  Do not expect anything
resembling sanity.

>and how to get it to work properly?

Do not use an alias.

The C shell's `parser' looks for a *line* whose first word is `else' or
`endif' after the C shell executes a false `if (expr) then'.  While
scanning for such a line it notes lines that have the form

	if<whitespace>.*<whitespace>then

and increments a `false if' counter.  You can thus stick all sorts of
syntactic trash between a false `if' and its corresponding `endif'; only
when the test in the `if' becomes true will the C shell actually notice
that the trash is indeed invalid.  For instance:

	if (0) then
		if (look, unclosed { and !funny characters then
		endif
		echo this does not get echoed
	endif
	echo but this does

It *is* possible to jam a newline into an alias, but if you do you will
quickly run afoul of other C shell bugs.  For instance:

	% alias t 'if (0) then\
		echo foo\
	endif\
	echo bar'
	% t
	? ? %

Nothing gets echoed.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 405 2750)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris