Need help in 'at' command

Hello,
While using the 'at' command it works when I pipe the command I
want to schedule to 'at'

So
$ date | at now + 2 minutes works well.
but
a) $ ls -l | at now + 2 minutes accepts the job, but gives a very
strange output in /var/spool/mail/root....

b) $killall <exec name> | at now + 2 minutes results in killall
getting executed immediately...

Am I missing something while using 'at' with those commands which have
some parameters/switches.
Also how do I get the output on the screen instead of .../mail/root..
Do I use some other command to schedule jobs using shell scripts.

Thanks,
R C
.

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