luj@gus17.ecn.purdue.edu (Jun Lu) (03/25/91)
The following attached script can be executed by typing its file
name(say test.sh) w/ no problem. "sh -x test.sh" also works OK.
But if I try to use the "at -s <time> test.sh", the problem arises.
I got the output(mail) like this:
---
Your "at" job "7148" produced the following output:
gus ... 10:56pm up 2 days, 5:05, 1 user, load average: 5.82, 6.24, 6.34
OK
___
But where is the output for 2nd machine ?
By the way the other day /bin/sh reported a syntax error(from within at),
complaining "unexpected end of file", even though "sh -x test.sh"
worked fine. I thought there might be some hidden char in the file, so
I manually retyped the script using vi(not emacs). This time I got the
above "truncated" output.(Admittedly, I got other various complaints
from at during debugging, complaining /bin/sh encountered some
syntax/parsing error. But I really can not reproduce them now.
I also jsut rebooted "my" sun3/60 with a 'k2" ...)
Can you guru out there tell me what is wrong(sh problem, rsh problem
at problem, or my problem) ? I'm running under Sun3/60(and Sparc) with
SunOS4.0.x. Thanks in advance.
--------- script(devised to illustrate the problem) ---
#! /bin/sh
# NOTE: The intent of this script is NOT to test if the remote machine
# is died; rather it is used to to illustrtate the problem
#
PATH=/usr/ucb:/bin:/usr/bin
export PATH
USER=luj
HOST=gus
echo -n "$HOST ..."
if rsh -l $USER $HOST uptime
then
echo OK
else
echo died
fi
USER=on5
HOST=mace.cc
echo -n "$HOST ..."
if rsh -l $USER $HOST uptime
then
echo OK
else
echo died
fi
--------------- end of the script --------------
--
-- Jun Lu Internet:luj@ecn.purdue.edu --
-- Aeronautics & Astronautics Bitnet: luj%ecn.purdue.edu@purccvm --
-- Purdue University UUCP: pur-ee!luj --
-- W. Lafayette, IN 47907 Phone:317-494-9410 Fax:317-494-0307 --pfalstad@phoenix.Princeton.EDU (Paul Falstad) (03/25/91)
luj@gus17.ecn.purdue.edu (Jun Lu) wrote: >Your "at" job "7148" produced the following output: > >gus ... 10:56pm up 2 days, 5:05, 1 user, load average: 5.82, 6.24, 6.34 >OK >___ > >But where is the output for 2nd machine ? ... >echo -n "$HOST ..." >if rsh -l $USER $HOST uptime >then > echo OK >else > echo died >fi The problem is that rsh eats up its standard input, which also happens to be the shell script you're executing, since at gives your script to the shell as standard input. So when you rsh to the first host, while you're waiting for uptime to execute, rsh reads its input (your shell script), and sends it over the socket. Then uptime exits without reading anything. Now when the shell wakes up and tries to read the rest of your script, it gets an EOF, since rsh has eaten up all its input. The reason that the shell managed to print the OK is because the rsh was part of a control structure; the shell read in the whole if ... fi structure before executing rsh. Nothing after the fi was executed. You can try for yourself that if you put the whole script in braces { }, forcing the shell to parse all of it before executing, it will work fine. The easiest way to fix this is just to use the -n flag of rsh. rsh -n -l $USER $HOST uptime Read the FM for more information. -- Paul Falstad, pfalstad@phoenix.princeton.edu | 10 PRINT "PRINCETON CS" [Your blood pressure just went up.] | 20 GOTO 10 Princeton University would like to apologize to everyone for this article.