Prcoessing outoput from tail

ruby-talk
1

Hello,

I am trying to figure out how to perpetually process the output from a file. That is I continuously want to process output that is appended to a file and that file could get rolled out at any time. I use popen w/tail, but this opens the file each time and I have to reprocess all the files content. Is there a better way to do this or a library that would help me? I know that I could probably open the file, tack location, and watch the inode to make sure the file has not been rolled, but that amounted to a lot of mistakes and I could never get it work properly.

Thanks for the help!
Phy

···

____________________________________________________________________________________
Now that's room service! Choose from over 150,000 hotels
in 45,000 destinations on Yahoo! Travel to find your fit.
http://farechase.yahoo.com/promo-generic-14795097

2

Phy Prabab wrote:

Hello,

I am trying to figure out how to perpetually process the output from a file. That is I continuously want to process output that is appended to a file and that file could get rolled out at any time. I use popen w/tail, but this opens the file each time and I have to reprocess all the files content. Is there a better way to do this or a library that would help me? I know that I could probably open the file, tack location, and watch the inode to make sure the file has not been rolled, but that amounted to a lot of mistakes and I could never get it work properly.

Thanks for the help!
Phy

____________________________________________________________________________________
Now that's room service! Choose from over 150,000 hotels
in 45,000 destinations on Yahoo! Travel to find your fit.
http://farechase.yahoo.com/promo-generic-14795097
  

Check out the file-tail gem:

http://file-tail.rubyforge.org/

Cheery-o,
Gustav Paul

3

I am trying to figure out how to perpetually process the output from a
file. That is I continuously want to process output that is appended to a
file and that file could get rolled out at any time.

I guess this is a follow-on to this thread:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/240367

Have a look at using "tail -F=<filename>" or "tail -f=<filename> --retry"
within popen.

Screen 1:
$ tail -F /tmp/foo
tail: cannot open `/tmp/foo' for reading: No such file or directory

Screen 2:
$ echo "abc" >/tmp/foo; sleep 3; mv /tmp/foo /tmp/foo2; echo "def" >/tmp/foo

Now Screen 1 shows:

tail: `/tmp/foo' has appeared; following end of new file
abc
tail: `/tmp/foo' has been replaced; following end of new file
def

(read 'man tail' for more details. The above example is using tail 5.93 from
GNU coreutils, which comes with Ubuntu Linux 6.06)

I know that I could probably open the file, tack location, and watch
the inode to make sure the file has not been rolled, but that amounted to
a lot of mistakes and I could never get it work properly.

Let 'tail -F=<filename>' do that for you :slight_smile:

Brian.

···

On Sun, Mar 25, 2007 at 07:30:33AM +0900, Phy Prabab wrote: