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How do I rotate files in Unix?

On Solaris I have cron job which creates some log files and it puts it under a directory, this directory name is created based on system date for example directory name are like 08162005, 08172005 so on..

What I need is I want to do a rotation for these log directories every 14 days since these are directories with system dates, I am having little trouble getting this done,

Is there any way you can solve this for me??


Dave's Answer:

If you're trying to figure out how to do date math, then this is going to seem like a very difficult task. But, in fact, what you're talking about is a perfect job for one of the Swiss Army Knives of the Unix command line: find.

Specifically, find has a flag -ctime which lets you test how long ago the file was created. The notation that the program uses for specifying dates is a bit confusing, but I'll give you a shortcut: "-ctime" lets you specify the number of days, so the command "-ctime 14" sounds right, but it actually will only match files that are exactly fourteen days old.

What we want instead, however, is "fourteen days or older", which is done by prefacing the number with a "+".

Put everything together with the peculiar syntax of find and, if you're looking for files in the directory "/var/log/test", you could use:

find /var/log/test -ctime +14 -print

That'll work to identify these files, but what you're actually asking me is about directories that have this naming scheme, and it turns out that you can add another constraint to find that'll limit its results to just directories.

For this, I'm going to assume that your directories all live under the "/var/log/test" directory, but that's easily changed, of course.

To constrain results to just directories, use -type d ("-type f" is just files, for example). Put it together and:

find /var/log/test -ctime +14 -type d -print

That should identify the files you want. To automatically delete them, use "xargs" thusly:

find /var/log/test -ctime +14 -type d -print |
xargs /bin/rm -f

That should do exactly what you seek!



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Comments

One question. Can't you leave the "-print" arg off? It seems to default to print in all environments I've used (Solaris, Fedora, cygwin).

Erik

Posted by: Erik Weibust at August 29, 2005 5:59 PM

You're correct, Erik. I'm just an old-fashioned purist about this stuff. :-)

Posted by: Dave Taylor at August 29, 2005 7:09 PM

Erik-

I would suggest that the most portable way to write the script is to use the -print option to expressly state your intent.

If you assume that it works in all environments, it may behave unexpectedly.

We always use -print even if it is the default because we have multiple versions of OS's and not all of them support it by default.

It makes it easier to develop scripts this way.

Posted by: Jim at May 7, 2007 8:32 AM

If that pipe comes back empty, won't the rm -f act on the contents of whatever the current directory is?
Thanks,
Al

Posted by: Al at June 22, 2008 7:33 AM

Good question, Al, but actually "xargs" shouldn't even invoke the given command if there's no data sent to it in the first place. Kind of breaks the pipe metaphor, but in a good way.

Man page:

"The xargs utility exits immediately (without processing any further input) if a command line cannot be assembled"

Posted by: Dave Taylor at June 24, 2008 11:24 AM

Thanks so much! This is exactly what I was looking for. :)

Posted by: Jason Fare at May 1, 2009 11:04 AM

I have something to say, now that you mention it, but ...
Starbucks coffee cup I do have a lot to say, and questions of my own for that matter, but first I'd like to say thank you for all your efforts on this Web site by buying you a cup of coffee!

I do have a comment, now that you mention it!











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