Re: test incorrectly rejecting valid expression with confusing ! placement

[Eric Blake <eblake@redhat.com>]

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[adding the Austin Group]

On 09/03/2013 11:03 PM, Herbert Xu wrote:
> On Wed, Sep 04, 2013 at 01:20:00PM +1000, Herbert Xu wrote:
>>  
>>> "test ! -o !" is a three-argument test, where $2 (-o) is a binary
>>> primary, so it is the binary test of $1 and $3, and the end result is an
>>> exit status of 0.  Bash and ksh get it right, dash fails.
>>
>> Both zsh and posh do it like dash:
>>
>> $ zsh -c 'test ! -o !'; echo $?
>> zsh:test:1: too many arguments
>> 1
>> $ zsh -c 'test ! = !'; echo $?
>> 0
>> $
> 
> Another case in point is 'test ! = -o a', here bash differs with
> every other shell installed on my system, which all return 0, just
> like dash.

GNU coreutils behaves like bash; the POSIX wording justifies bash:

4 arguments:

        If $1 is '!', negate the three-argument test of $2, $3, and $4.

        [OB XSI] [Option Start] If $1 is '(' and $4 is ')', perform the
two-argument test of $2 and $3. [Option End]  On systems that do not
support the XSI option, the results are unspecified if $1 is '(' and $4
is ')'.

        Otherwise, the results are unspecified.

That is, "test ! = -o a" should be parsed as "test ! \( = -o a \)"
(bash's behavior, per the first bullet), not "test \( ! = \) -o a"
(ksh's behavior, per the third bullet).

Yet another reason why the XSI -a and -o make the parsing precedence of
test a pain to decipher.  Do we need to open yet another bug against
POSIX to allow for ksh's behavior?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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