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cdecker
Asked: 2012-01-15 16:39:59 +0800 CST

Sending mail from command line if body not empty

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I'd like to write a simple script that alerts me if a log changes. For this I'm using grep to find the lines I'm interested in. Right now it works like this:

grep line /var/log/file | mail -s Log [email protected]

Problem is that this sends a mail even if no matching lines are found. The mail utility from GNU Mailutils seems to have no switch telling it to drop mails that have an empty body.

Is there a quick and easy way to do so?

email bash cron command-line-interface gnu

3 Answers

  1. Best Answer
    output=$(grep line /var/log/file); [[ -n "$output" ]] && mail -s Log [email protected]

    Or you can make this into a cron job and then if it produces any output it will email the users. You can edit the /etc/aliases file (and then run newaliases command) to send mail to address not on the box.

    Ex of cron entry (You won't be able to set the subject line thogh

    1 0 * * *  grep line /var/log/file

    Or you can get the ifne utility - This is probably what you want

    grep line /var/log/file | ifne mail -s Log [email protected]

    The ifne command it availabe from the epel repo for centos and RHEL. I can't find a link to the man page online but there it is

    ifne(1)
    ifne(1)

    NAME ifne - Run command if the standard input is not empty

    SYNOPSIS ifne [-n] command

    DESCRIPTION ifne runs the following command if and only if the standard input is not empty.

    OPTIONS -n Reverse operation. Run the command if the standard input is emp- ty.

              Note  that  if  the  standard  input  is not empty, it is passed
          through ifne in this case.

    EXAMPLE find . -name core | ifne mail -s "Core files found" root

    AUTHOR Copyright 2008 by Javier Merino 

       Licensed under the GNU GPL

                              2008-05-01                           ifne(1)
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  2. "man mail" tells me that the argument -E stopps sending mails if body is empty. works fine for me.

    -E

    If an outgoing message does not contain any text in its first or only message part, do not send it but discard it silently, effectively setting the skipemptybody variable at program startup. This is useful for sending messages from scripts started by cron(8).

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  3. See https://unix.stackexchange.com/a/100720/27458

    Just use ifne:

    grep line /var/log/file | ifne mail -s Log [email protected]
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