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List:       procmail
Subject:    RE: mkdir
From:       "Dallman Ross" <dman () nomotek ! com>
Date:       2000-05-14 1:05:53
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Aaron Schrab <aaron@schrab.com> wrote:

> At 14:17 +1200 27 Apr 2000, Volker Kuhlmann 
> <kuhlmav@elec.canterbury.ac.nz> wrote:
> > > > 	# Most efficient way to test & mkdir
> > > > 	:0 ihc
> > > > 	* ! ? test -d $DIR
> > > > 	|mkdir -p $DIR
> > 
> > >         :0 wic  # if needed, create today's ackdir; add sender
> > >         * $ ! TESTNAME ?? ^^$ACKS/fullacks/
> > >         | test -d $ACKS/$DATE || mkdir $ACKS/$DATE ;\
> > 
> > I'd say the efficiency is the same. Both versions run the external
> > program test, and mkdir if the test fails.
> 
> Not true.  The second way runs a shell which then runs the commands.
> The first way runs the commands directly, so there's one less process
> used.

While I agree with you, Aaron, after looking it over, I gave up
on trying to change mine anyway.  The reason is that mine is checking
an extra condition, and I don't see an easy way to get all that in
a recipe of the first (Philip's man page) format.

I tried, tentatively,

        :0 whic  # if needed, create today's ackdir; add sender
        * $ ! TESTNAME ?? ^^$ACKS/fullacks/ 
        * ! ? test -d $ACKS/$DATE
        | mkdir -p $ACKS/$DATE;\ 
           lockfile -r0 $ACKS/$DATE/"$FROM"

        # We use lockfile in a nonstandard way[1], relying on the
         # lagniappe of how it handles exit codes to avoid a possible
          # race condition.  -r0 says don't retry.  (Mainly only
           # another cascaded invocation of procmail would have
            # yielded a failure, anyway.  :-)

              # [1] I.e., we're not using it as a semaphore but to
               # create a durable file.


However, it was immediately clear to me that the lockfile trick to
create a file would not be initiated under this algorithm if there 
had been no dir to begin with.  Under my original algorithm, it
all works.

I see that I could divide it up into two recipes, maybe with

	:0 A
     | lockfile -r0 $ACKS/$DATE/"$FROM"

as the second one.  But now we have two recipes to do what one
short one did before.  I don't know if it's worth saving one
shell invocation.  I am interested in efficiency and elegance,
both.  Here we seem to have a conflicting balance between the
two.  Comments?

I also have a question.  I thought I needed "$" near the left
in condition lines when I am relying on a variable of mine in
the condition line.  How come we don't need the "$" in the test -d
line above?  This confuses me.

-- 
Dallman Ross <dman@nomotek.com>
U.S. Voicemail/FAX: +1 (415) 680-2388
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