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Thread: Using expect with Cron

  1. #1
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    Using expect with Cron

    Hi

    I have not done a lot with Expect, but I am hoping someone can figure if I am doing something that should not be done here or if I am misusing cron.

    I have written an expect script to extract info from a non-snmp capable device.

    The expect script logs into my target via ssh , runs a few commands here and there, gets usage, users, active sessions and so on and quits.

    When I run it it works fine, grabbing the info I need.
    I can also then pipe to tee and it captures in a file for me.
    This all seems to work well.

    I then try and be a smarty pants and place it in cron to run twice every hour
    I have a few of these scripts to a few devices so have a few more entries in cron, but here is one example.

    Code:
    8,38 * * * * $HOME/scripts/script.exp | tee -a $HOME/stats/`date +\%H\%M_\%m\%d_\%Y_device`.log 2>&1

    The file is created.
    However, Im seeing some files truncated like the thing quits before its done.
    I would think its a timing or matching thing in expect, but this only happens when I place in cron
    I tried placing in sleeps and different expect criteria but it always stops at the same point.


    Am I misusing expect or cron here? Is there something I am not doing in Cron that I should be doing? Is there something in my statement that wrong? Is it some idiosyncrasy with cron I'm not aware of?



    Thanks a mill

    jonobr

    PS 10.04 LTS , and now as I write, Im thinking of upgrading just to see if its that!
    You can tell a man who boozes by the company he chooses, as the pig got up and slowly walked away.

  2. #2
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    Re: Using expect with Cron

    Your script may not be finding the programs. You might need to set a path in your crontab. Look on this page for an example of how I manage a crontab schedule.

    Also, are you checking return codes from the programs your scripts are calling? Those codes can get you key information on what is going wrong.

    Example:
    Code:
    aptitude safe-upgrade --assume-yes --target-release `lsb_release -cs`-security >> ${LOGFILE} 2>&1
    ReturnCode=$?
    if [[ "${ReturnCode}" -gt 0 ]]; then
      ErrorFlag=8
      echo "Script failed.  aptitude return code is ${ReturnCode}" | tee -a ${LOGFILE}
    fi

  3. #3
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    Re: Using expect with Cron

    Hi LHammonds

    Thanks for the response,

    Its running the program alright as the files are created and those files are either fully populated or half populated with he data I need.

    Im not sure its a return code thing but that's something I think I should look at,

    thanks for the pointer!!


    Jonobr
    You can tell a man who boozes by the company he chooses, as the pig got up and slowly walked away.

  4. #4
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    Re: Using expect with Cron

    tee is for duplicating output, i.e. both to your screen and to a file.

    So why you need that in a cron job ?

    if nothing else, it makes the cron job line needlessly complicated; you could just dump the output in a file.
    Not sure if this has anything to do with the problem you're describing, but weeding out the cruft certainly won't harm.

    Also, ssh + expect is a bit silly, as ssh has built-in capabilities for passwordless logon. https://help.ubuntu.com/community/SSH/OpenSSH/Keys (But maybe that's not possible with the device in question)



    it always stops at the same point.
    and what point is that ?

  5. #5
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    Re: Using expect with Cron

    Hey Koenn


    You may have a point there,

    Let me try redirection in Cron and see if that works

    Thanks!!

    Jonobr

    PS- I cant use keyless as the target device is a vxworks box that wont let me copy across or insert a public key..
    You can tell a man who boozes by the company he chooses, as the pig got up and slowly walked away.

  6. #6
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    SOLVED Using expect with Cron

    Hello


    I had two main problems with my expect script and cron.
    One was using tee which koenn pointed out was incorrect.

    The second thing that got me was that I was using an incorrect escape from my script that caused it to hang.

    When I closed the session I spawned it seemed to tick along a lot better.

    Thanks all for your help!!

    Jonobr
    You can tell a man who boozes by the company he chooses, as the pig got up and slowly walked away.

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