Re: Reliable/safe way of removing empty maildirs?

[Paul Hoffman <nkuitse@xxxxxxxxxxx>]

On Thu, Dec 06, 2007 at 11:47:53AM -0600, Kyle Wheeler wrote:
> On Thursday, December  6 at 11:40 AM, quoth Paul Hoffman:
> >> chmod a-w dir/new
> >> if [ `find dir -type f` ] ; then
> >
> > You have to do something like this instead:
> >
> > found=`find dir -type f`
> > if -n "$found" ; then
> >
> > At least on my system (Mac OS X 10.3 = Darwin 7.9.0), where find(1) 
> > exits with status 0 even if nothing is found.
> 
> That's why I used the form that I used. Consider what I said; I said
> 
>      if [ `find dir -type f` ] ; then
> 
> I did not say:
> 
>      if find dir -type f ; then
> 
> The reason is because the former relies on the output of find, and the 
> latter relies on the exit status of find. In other words, I had 
> already addressed this issue.

Right, sorry.  I was going to say to use the exit status of find(1), but
then realized that wouldn't help.

> At worst, some shells might require that 
> to be rewritten like this:
> 
>      if [ "$( find dir -type f )" ] ; then

Or using backticks:

    if [ "`find dir -type f`" ]; then

I don't know if that's any more portable, though.

> The reason for that is that [ (also known as /bin/test, and frequently 
> a builtin shell command) returns true if it has any arguments of any 
> non-zero length, and returns false if it does not (i.e. the -n 
> argument is the default behavior).

Thanks -- I didn't know that.

> My example is equivalent to this:
> 
>      found=`find dir -type f`
>      if [ "$found" ] ; then
> 
> ...but does not require the extraneous variable definition.

Hmm, my test (builtin, bash 2.05b.0) can't be relied upon:

                $ PS1='\n\$ '

                $ mkdir foo; cd foo
                /User/nkuitse/dt/foo

                $ builtin test `find . -type f` || echo No files
    OK    -->   No files

                $ touch bar

                $ builtin test `find . -type f` || echo No files
    OK    --> 
                $ touch baz

                $ builtin test `find . -type f` || echo No files
                bash: test: ./bar: unary operator expected
    Oops! -->   No files

/bin/test messes up in the same way, just with a different error
message.  YMMV of course.

> ~Kyle

Paul.

-- 
Paul Hoffman <nkuitse@xxxxxxxxxxx>