Date: Fri, 29 Jun 2001 00:27:58 -0400 From: parv <parv_@yahoo.com> To: Dave Tweten <tweten@nas.nasa.gov> Cc: freebsd-questions@freebsd.org Subject: Re: Bourne Shell Syntax Wierdness Message-ID: <20010629002758.A3157@moo.holy.cow> In-Reply-To: <200106290144.f5T1itu01729@gilmore.nas.nasa.gov>; from tweten@nas.nasa.gov on Thu, Jun 28, 2001 at 06:44:54PM -0700 References: <200106290144.f5T1itu01729@gilmore.nas.nasa.gov>
next in thread | previous in thread | raw e-mail | index | archive | help
so, Dave Tweten shared this in my lifetime...
> The sh man page says that the two operators "||" and "&&" have the same
> precedence. It also says that
>
> a || b
>
> means "execute b if a terminates abnormally" and
>
> a && b
>
> means "execute b if a terminates normally."
>
> So I don't understand why
>
> true || true && echo Oops!
>
> prints "Oops!"
>
> This is apparently not a bug in FreeBSD sh, because IRIX, IRIX64, and SunOS
> Bourne/Korn shells work the same way, but it certainly runs counter to my
> ability to read English and the contents of the man page.
>
> Incidently,
>
> true || { true && echo Oops! }
>
> prints nothing -- which I would have expected with or without the "{}".
>
sh & ksh man pages do say the quoted behaviour above. so does bash's.
however, bash's page adds this, under "Compund Commands" which is
missing for sh & ksh:
The && and || operators do not execute expression2 if the
value of expression1 is sufficient to determine the return
value of the entire conditional expression.
notice the word "sufficient"; so due to lack of proper grouping, to
mitigate ambiguity, all three evaluates the expression as...
# ( true || true ) && echo Oops!
...i may be stating the obvious; mind you that i am only hypothisizing
here, nothing more than that, lest somebody is bent on getting the above
desired evaluation...
--
so, do you like word games or scrabble?
- parv
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20010629002758.A3157>