How to do a blocking readdir or similar

bigcreeklinn has asked for the wisdom of the Perl Monks concerning the following question:

Thanks all, for your help. As an OLD unix type, I only thought of solving the problem in that domain. With your pointers, I learned just enough Applescript to call perl from a Folder Action. I have only done "date >>/tmp/timestame" so far, but that proves the process. I also will try to load and use the IO::Kqueue package. That looks like just the ticket for a perl-only approach. Again, thanks. --Linn ------------------------------ Greetings. On my Mac OS X machine, I would like to drag a file to a folder and as it is dropped in, to wake up my perl script. My first attempt was to create a named pipe and have my script waiting on an open function. This worked great for something like cat somefile >mynamedpipe but unfortunately, the application I wanted to export from would not write to the pipe. It needed to delete it and write a normal file. So now I am looking at alternatives. It would be easy to modify the script to process some file that has been written or dropped into a directory, but I would like to control it with something more elegant than polling the directory on a sleep timer. I searched somewhat throught CPAN but didn't see anything initially. Any ideas? Thanks.

Comment on How to do a blocking readdir or similar

Replies are listed 'Best First'.
Re: How to do a blocking readdir or similar by BorgCopyeditor (Friar) on Dec 19, 2005 at 03:31 UTC
Which version of OS X? This is probably a job for so-called "Folder Actions" (10.3 Panther and later) which allow you to fire off a script in response to adding files. Then you'll need a bit of AppleScript (using "on adding folder items") that fires off your perl script (using "do shell script"). A good PerlMonks-ish site to look for this sort of thing is http://bbs.applescript.net. Good luck. BCE --Your punctuation skills are insufficient!	[reply]
Re: How to do a blocking readdir or similar by merlyn (Sage) on Dec 19, 2005 at 03:12 UTC
POSIX doesn't provide such a hook, so most unix-like systems also don't have such a hook. Your solution of polling is probably the best portable solution. However, if you're smart enough with AppleScript, you can attach an applescript action to a folder drop, which can then launch your Perl program. I'm not that smart, or I'd point you at a ready solution. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^2: How to do a blocking readdir or similar by saintmike (Vicar) on Dec 19, 2005 at 04:08 UTC
POSIX doesn't provide such a hook, so most unix-like systems also don't have such a hook Actually, Linux provides such a hook. Check out SGI::FAM for using the file alteration monitor based on dnotify or Linux::Inotify2 for newer kernels.	[reply]
Re^3: How to do a blocking readdir or similar by Kanji (Parson) on Dec 19, 2005 at 06:25 UTC
OS X (which the OP was using) shares more with FreeBSD than Linux, so IO::KQueue is probably a more appropriate choice. From the README... This module is a low level interface to the FreeBSD and Mac OS X kqueue() system call. This is basically equivalent to epoll() on Linux - a high performance poll() replacement. --k.	[reply]
Re^3: How to do a blocking readdir or similar by james2vegas (Chaplain) on Aug 24, 2009 at 07:38 UTC
SGI::FAM seems like a more compatible and less linux-only solution, and fam should run on Mac Os X (and BSDs of all stripes really, as it can be compiled to run with kqueue Update: Maybe that is not such a good recommendation, SGI::FAM depends on deprecated File::PathConvert, has an unregistered dependency on Test::Helper and doesn't find my libfam without help. After that, it does seem to work, though, quite well, though only on famd started as a daemon, not running through inetd.	[reply]
Re^2: How to do a blocking readdir or similar by GrandFather (Saint) on Dec 19, 2005 at 03:27 UTC
That's not smartness, just knowledge. :) DWIM is Perl's answer to Gödel	[reply]
Re^2: How to do a blocking readdir or similar by brian_d_foy (Abbot) on Dec 19, 2005 at 13:26 UTC
I describe the Mac side of the process in Automatically Import Images into iPhoto. To launch a Perl script, just call it from the AppleScript that the folder action wants. It sounds like the poster will have an annoying little synchronization problem though: the AppleScript creates a semaphore somehow, and the sleeping, blocking script has to check for that. Perhaps the two scripts could talk to each other in some other way, though. -- brian d foy <brian@stonehenge.com> Subscribe to The Perl Review	[reply]
Re: How to do a blocking readdir or similar by john_oshea (Priest) on Dec 19, 2005 at 11:48 UTC
If you're running Tiger, I'd take a look at launchd which can, amongst many other things monitor paths for changes. This would save you from having to wrestle with AppleScript's "quirks", at the cost of having to write Yet Another XML File. There's some introductory stuff here: "Getting Started with launchd" from the Apple Developer site "launchd in Depth" from afp548.com	[reply]
Re: How to do a blocking readdir or similar by aquarium (Curate) on Dec 19, 2005 at 13:03 UTC
tail --retry -f file_you_are_expecting \| perl your_perl_script.pl the hardest line to type correctly is: stty erase ^H	[reply]