bash test -n && test -z return tru

[Christopher Faylor]

On Fri, Aug 19, 2005 at 07:27:55PM +0000, Eric Blake wrote:
>> On Fri, Aug 19, 2005 at 03:01:19PM -0400, Poor Yorick wrote:
>> >from reading the bash man pages, I would have thought the -n and -z were 
>> >mutually exclusive.  Therefore I don't understand this result:
>> >
>> >~>$ [ -n $(which nonexisingfilename 2>/dev/null) ] && [ -z $(which 
>> >nonexistingfilename 2&>/dev/null) ]  && echo hello
>> >hello
>> >~>$
>> >
>> >can anyone help explain this?
>> 
>> This defaults to
>> 
>>   [ -n ] && [ -z ] && echo hello
>> 
>> I would have expected a syntax error in that case.
>
>Nope.  POSIX requires that when there is one argument, it evaluates
>to true if it is not empty.

Thanks for the clarification.

>Neither -n nor -z is empty, so they are both true.  Remember, if there
>are no quotes around a word, it is subject to field splitting, such
>that an empty string disappears from the argument list altogether, and
>you are only giving one argument to [.

Er, yeah.  That's what I meant when I said:

"This defaults to:

  [ -n ] ..." ?

and then mentioned that the argument had to be quoted.

cgf

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