Mail Archives: cygwin/2005/08/19/15:28:13
> 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. 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 [.
>
> Regardless of that, however, if you want to actually make this work you
> need to do something like:
>
> [ -n "$(which nonexisingfilename 2>/dev/null)" ]
Yep - adding the quotes now forces the second word to remain,
even if it is empty, and with two arguments to [, -n and -z now
become mutually exclusive unary operators instead of strings.
--
Eric Blake
volunteer cygwin bash maintainer
--
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Problem reports: http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
FAQ: http://cygwin.com/faq/
- Raw text -