RE: Cron Problem

From: David Christensen (dpchrist_at_holgerdanske.com)
Date: 04/30/05

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    To: <debian-user@lists.debian.org>
Date: Sat, 30 Apr 2005 00:23:02 -0700

    I wrote:
    >> Have you redirected stdout to stdin ...

    Graham Smith wrote:
    > ... (I think you mean stderr to stdout).

    Yes. My mind jelly turning into seems to be lately... :-)

    > Although I've been using Linux for a while I haven't learnt much
    > about the shell.

    Get this book:

        http://www.oreilly.com/catalog/bash3/index.html

    > ... abandons it's output and relies on cron to mail it to me.

    I find it's easier/ faster to debug if I dump everything into a log file. YMMV.

    > just the amount of time it takes to run.

    I had similar questions, and that's why I put the `date` invocation into the
    scripts run by cron:

        echo ===== `date` ===== end: '$Id: cron-backup,v 1.9 2004/12/08 0
    5:59:11 dpchrist Exp $' ===== 2>&1 | tee -a $LOG

    Without the Bash book and knowledge of CVS, the above line may look like
    gibberish. I'll try to translate:

        echo the echo(1) command -- print command-line arguments on
               stdout

        ===== something that's easy to see in a crowded log file.

        `date` invoke the date(1) command and substitute the output in this place

        end: a string that matches a similar "begin:" line earlier in the script

        '$Id: cron-backup ...$'
               I keep this script under version control using cvs(1). $Id$
               is a CVS keyword that is expanded by cvs whenever I check out
               the file. It is enclosed in single quotes so that the bash
               shell doesn't try to execute any of the stuff in there.

         2>&1 redirect stderr to stdout

         | send the stdout of the previous command to the stdin of the
               next (shell command pipe)

         tee the tee(1) command -- copies stdin to stdout and stdin to a
               file

         -a append option for tee(1) command

         $LOG expanded by the Bash shell to be the value of the shell
               variable LOG; e.g. the name of the log file

    BTW here is the book for CVS:

        http://cvsbook.red-bean.com/

    HTH,

    David 

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