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From: jsdy@hadron.UUCP
Newsgroups: net.unix-wizards,net.bugs.4bsd
Subject: Re: C-Shell weirdness
Message-ID: <344@hadron.UUCP>
Date: Sat, 29-Mar-86 03:21:00 EST
Article-I.D.: hadron.344
Posted: Sat Mar 29 03:21:00 1986
Date-Received: Tue, 1-Apr-86 07:16:13 EST
References: <676@nbires.UUCP>
Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao)
Distribution: net
Organization: Hadron, Inc., Fairfax, VA
Lines: 28
Xref: watmath net.unix-wizards:17407 net.bugs.4bsd:2024
Summary: only re: if ($arg == '-b')

In article <676@nbires.UUCP> nose@nbires.UUCP (Steve Dunn) writes:
>           if ($arg == '-b') echo 'UNIX is fun'
>Will get the error "If: missing filename" if $arg happens to equal
>-x or -e or any of the other constructs used to test file attributes.
>	 if (x$arg == 'x-b') echo 'UNIX is fun'
>Is there a better way to do this and why does this happen in the first
>place?

[The rest of this was ably answered elsewhere.  HOWEVER ...]

Consider what the command line is when $arg is -e or -x or whatever:
	if (-e == '-b') ...
Now, doesn't that just look like it's asking to evaluate -e on file
"==", or something like that?  Of course the parser recognises "=="
as a relation, and so complains instead that there's no file name.

Your alternative is actually a venerable shell-script idiom to cancel
the flag effect of the "-".  However, you really should put $arg in
double-quotes to negate the effect of an in-valid string:
	set arg = "-b -e"
	if (x$arg == '-b')
becomes
	if (x-b -e == '-b')
with who knows what syntax error reports.  I'd use:
	if ("X$arg" == "X-b") ...
-- 

	Joe Yao		hadron!jsdy@seismo.{CSS.GOV,ARPA,UUCP}