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What is this line of code doing?

Can anyone please explain me what this line of code is doing:

1) daemon /usr/sbin/sendmail $([ "x$DAEMON" = xyes ] && echo -bd) $([ -n "$QUEUE" ] && echo -q$QUEUE) $SENDMAIL_OPTARG

2) daemon --check sm-client /usr/sbin/sendmail -L sm-msp-queue -Ac -q $SMQUEUE $SENDMAIL_OPTARG

These lines of code I have taken from sendmail script of Fedora Core, they seem to be too complex for me. Please explain as details as possible ;).

Thx a lot,
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jetli
Asked:
jetli
1 Solution
 
jlevieCommented:
The short answer is that they startup the MTA & MSP instance of sendmail. In both cases the actual launch of the sendmail binary is done by the daemon function from /etc/rc.d/init.d/functions. Its a "smart" function that tries to start the utility safely.

In the first line daemon will execute /usr/sbin/sendmail and build the argument list from the the variables:

If DAEMON=yes in /etc/sysconfig/sendmail -bd will be in the argument list from $([ "x$DAEMON" = xyes ] && echo -bd).

If QUEUE=?? in /etc/sysconfig/sendmail the value (??) will be used for the queue interval (e.g., -q1h) from $([ -n "$QUEUE" ] && echo -q$QUEUE)

And finally if there are any optional arguments (SENDMAIL_OPTARG) defined in /etc/sysconfig/network they'll be included.

The defaults of a RedHat/Fedora system would result in the following command line for starting Sendmail:

/usr/sbin/sendmail -bd -q 1h

In the second line the MSP instance is started in a similar manner. SMQUEUE will be set to the value of QUEUE (from /etc/sysconfig/sendmail) if it isn't otherwise defined. So the command looks like:

/usr/sbin/sendmail -L sm-msp-queue -Ac -q 1h
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