Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!usenet.ins.cwru.edu!cwns1!chet
From: chet@cwns1.CWRU.EDU (Chet Ramey)
Newsgroups: gnu.bash.bug
Subject: Re: More :${abc?abc} exits
Message-ID: <1990Jan8.221741.3193@usenet.ins.cwru.edu>
Date: 8 Jan 90 22:17:41 GMT
References: <9001052019.AA01516@dash.mitre.org>
Reply-To: chet@po.CWRU.Edu
Distribution: gnu
Organization: Case Western Reserve Univ. Cleveland, Ohio, (USA)
Lines: 31

In article <9001052019.AA01516@dash.mitre.org> barratt@dash.mitre.org writes:

>Brian,
>	With regard to John Ramsdell's question about parameter
>expansion:  The syntax
>	${param:?[value]}
>is supposed to substitute "param" if it is not null, otherwise it
>should write "value" to stderr.  If value is omitted, then sh writes
>	param: parameter null or not set

It does this when the shell is interactive.  When the shell is not interactive,
it exits.  The POSIX spec said nothing about interactive vs non-interactive
behavior (neither does the sh man page, as a matter of fact), so Brian 
just exited the shell after a bad substitution like that.  I `fixed' it to
mimic the sh behavior (`do what I do, not what I say'), and that's the 
code Brian is running now.

This is the full description from the System V sh manual:

${parameter:?word}

"If `parameter' is set and is non-null, substitute its value; otherwise, print
 `word' and exit from the shell.  If `word' is omitted, the message `parameter
 null or not set' is printed."

Chet Ramey
-- 
Chet Ramey
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chet@ins.CWRU.Edu