Prcoessing outoput from tail


#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


#2

Phy P. wrote:


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Check out the file-tail gem:

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

Cheery-o,
Gustav P.


#3

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

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=” or “tail -f=
–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=’ do that for you :slight_smile:

Brian.