[Sbcl-help] Re: useful code snippet

[Russell M. <rus...@ya...>]

Andreas Fuchs <as...@bo...> writes:

> Today, Russell McManus <rus...@ya...> wrote:
>>
>> While writing some code using run-program, I came upon the need for
>> the following:
>
> autobench uses a similar macro, so I have a few questions about your
> code.
>
> One, wouldn't it be better if the macro also bound
> *default-pathname-defaults* to the new-dir? (My implementation
> assumes that the user(me) will consistently use
> with-current-directory and so skips the whole getcwd thing in favor
> of just chdir-ing back into *d-p-defaults*)

I can easily be convinced that *default-pathname-defaults* should be
magical in some sneaky way.  I just threw together the macro that I
wrote based on an immediate need, and wondered whether someone else
had a fully baked solution.

>> (defmacro with-current-directory ((new-dir) &body body)
>>   (let ((start (gensym)))
>>     `(let ((,start (sb-unix:posix-getcwd)))
>>       (unless (char= #\\ (aref ,start (1- (length ,start))))
>> 	  (setf ,start (concatenate 'string ,start "/")))
>
> Two, what's with that #\\ check? In which cases does getcwd return the
> \ character as the last element?

This is an error in my code, the constant should be #\/, because
getcwd sometimes returns a path without a trailing slash, which when
parsed with parse-namestring will put the last path component into the
pathname's name field rather than the final component in the directory
field.

-russ