File name with yyyymmddhhmi Post: 303019989

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Top Forums UNIX for Beginners Questions & Answers File name with yyyymmddhhmi Post 303019989 by rbatte1 on Wednesday 11th of July 2018 01:30:25 PM

07-11-2018

Moderator

You also need to ensure that your file creation and all the output being put into it is Atomic, i.e. a single operation that takes a single IO. Often this is done by creating the file and building it up with content as another name and then when it is ready, renaming it to it appears as a complete file instantly.

If you have a file that takes even a whole second to build, then you may sometimes be unlucky and fetch a partial file.

Something like this would illustrate it:-

Code:

((random_delay=$RANDOM%9))

( sleep $random_delay ; cat /tmp/myfile ) &      # Display the file at some undetermined time

date                             > /tmp/myfile
echo "First data line of file"  >> /tmp/myfile
sleep 3
echo "Second data line of file" >> /tmp/myfile
sleep 3
echo "Last data line of file"   >> /tmp/myfile
wait                                             # In case the random delay is long, wait for the background sleep/cat to finish

If you run this repeatedly, you may get 1, 2 or 3 lines of output. You can compensate by the cat reading a file that is always the finished article, so more like:-

Code:

((random_delay=$RANDOM%9))

( sleep $random_delay ; cat /tmp/finalfile ) &   # Display the file at some undetermined time

date                             > /tmp/myfile
echo "First data line of file"  >> /tmp/myfile
sleep 3
echo "Second data line of file" >> /tmp/myfile
sleep 3
echo "Last data line of file"   >> /tmp/myfile

mv /tmp/myfile /tmp/finalfile                    # Atomic file write
wait                                             # In case the random delay is long, wait for the background sleep/cat to finish

It may fail first time if the file does not exist, but afterwards it would only ever read a completed file.

Doing this, you could also make a link as a "latest" file, so you always know which one to pick up.

I hope that this helps,
Robin

rbatte1

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processcsv.py

PROCESSCSV.PY(1)					      Virtualization Support						  PROCESSCSV.PY(1)

NAME

       processcsv.py - process virt-top CSV files

SUMMARY

	virt-top --csv data.csv
	processcsv.py < data.csv

DESCRIPTION

       virt-top is a top(1)-like utility for showing stats of virtualized domains.

       processcsv.py is a simple Python script that post-processes the output of "virt-top --csv".

       It is used like this:

	virt-top --csv data.csv
	processcsv.py < data.csv

       The second command will overwrite the following files in the current directory:

       "global.csv"
	   This contains the global (host) statistics columns from the CSV file.

       "domainNN.csv" (multiple files)
	   For each libvirt domain ID NN, a file is created containing the per-domain statistics from the CSV file.

SEE ALSO

       virt-top(1)

AUTHORS

       Richard W.M. Jones <rjones @ redhat . com>

COPYRIGHT

       (C) Copyright 2007-2012 Red Hat Inc., Richard W.M. Jones http://libvirt.org/

       This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by
       the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation,
       Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

virt-top-1.0.8							    2013-12-29							  PROCESSCSV.PY(1)