Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!eos!labrea!decwrl!pyramid!weitek!practic!vlsisj!bennett
From: bennett@vlsisj.VLSI.COM (Michael Bennett)
Newsgroups: comp.sys.apollo
Subject: Re: shell scripts, boolean variables, and eon
Message-ID: <2302@vlsisj.VLSI.COM>
Date: 6 Apr 88 18:27:18 GMT
References: <8803241941.AA09455@ELI.CS.YALE.EDU>
Reply-To: bennett@vlsisj.UUCP (Michael Bennett)
Organization: VLSI Technology Inc., San Jose, CA
Lines: 49

In article <8803241941.AA09455@ELI.CS.YALE.EDU> hanks-steven@YALE.ARPA (Steven Hanks) writes:
>executing the following shell script produces weird 
>results:
>     #!/com/sh
>     eon
>     truevar :=  true
>     falsevar := false
>     if ^falsevar     then args "yes" else args "no" endif
This line doesn't work right.  (Output is 'yes')

>     if ((^falsevar))     then args "yes" else args "no" endif
And this one does.  (Output is 'no')

My experiment yielded the same results.  I'll bet DOMAIN/IX is interfering.
In /bin are scripts called true and false which return (exit 0) and
(exit 1) respectively.  This works fine for /bin/csh, but not for /com/sh
since the /com/sh command exit is for exiting loops, not exiting shells.
Thus, when /com/sh interprets ^falsevar, it replaces it with the text
'false' (it may be arguable wether or not this is the appropriate action for a
boolean variable with eon), and calls the /bin/false shell which just exits a 
non-existent loop and returns with a status of true.

The line above with ((^falsevar)) works because after the text 'false' is
substituted for ^falsevar, the expression is evaluated and returns a value
of false.

My discussion assumes the DOMAIN/IX /bin directory exists and is on your
search path.  If either of these aren't true, then maybe you have a false
command somewhere else on your search path.  Try this to find out where:

$ sh -n -x <</
$_ false
$_ /

(This returns '/bin/false' for me.)

If you take this off your search path, then the first case above still
doesn't work, and returns:

?(sh) "false" - name not found (OS/naming server)

To make the first case above work the way you want, you could write /com/sh
scripts which mimic the /bin/csh scripts for true and false.  They would
have one line, (return -t) and (return -f) respectively (look at the
Apollo help file for return).

--
Michael Bennett   (408) 434-7851 (W)
ARPA: bennett@lundy1.vlsi.com    [or bennett%lundy1.vlsi.com@parcvax.xerox.com]
UUCP: lundy1!bennett@vlsisj.uucp