standards/40639: /bin/sh doesn't expand PS1

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>Number:         40639
>Category:       standards
>Synopsis:       /bin/sh doesn't expand PS1
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    standards-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 14 08:50:00 +0000 2009
>Originator:     Alan Barrett
>Release:        NetBSD 5.99.7
>Organization:
Not much
>Environment:
System: NetBSD 5.99.7  i386
>Description:
        According to SUSv3 
<http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html>,
        the shell should expand the value of PS1 before printing it
        on every prompt.  NetBSD's /bin/sh does not do that.
>How-To-Repeat:
        It actually does this:

        $ ( cd /tmp ; ENV='' /bin/sh -i )
        $ PS1='${PWD} $ '
        ${PWD} $ 

        It should do this instead:

        $ ( cd /tmp ; ENV='' /bin/sh -i )
        $ PS1='${PWD} $ '
        /tmp $ 

>Fix:
        Expand PS1 when printing the prompt.