shell script challenge regarding background/prompt/pipe

[Kevin_31]

Hey experts. Is it as slow in the US as it is here in the UK now (just before Christmas)?

Anway, points for the genius who can make sense of the quagmire of concepts involved scripting the equivalent of pressing return at the end of a command which runs in background.

I need to run a script to start up a program after Omniback finishes a backup. We do this all the time here, but this time the program runs in background and the script doesn't return the prompt (return code?) therefore omniback thinks the script has failed when it eventually reaches it's timeout.

Running the script interactively I can see that it's kicked off the background process, e even echoes stuff which I stuck in AFTER the bg process. However, it doesn't give me the prompt back until I press return.

So, if I could send "^M" or echo "" or something similar, then connect it to the offending program with a pipe or "<" or something, I'd be in business.

I've looked up googlegroups and found some interesting discussions, but nothing which addressed my problem (either directly or indirectly).

I've tried stuff like:

echo ^M | nohup EXECUTABLE &
( echo ^M | nohup EXECUTABLE & )
echo "" | nohup EXECUTABLE &
echo "" | (nohup EXECUTABLE ) &
nohup EXECUTABLE & < echo ""
nohup EXECUTABLE & | xargs echo ""



I'm gonna be left with no choice but to take this bit o' background code out of the post-exec Omniback script and instead put it in a separate cron-job. This is untidy and not what I really wanna settle for.

So, I've come here... To the Great Source of all Knowledge and Wisdom!

cheers,
Kevin

[Elmar P. Kolkman]

Have you tried this:

nohup EXECUTABLE
where tmpf contains an empty line?

[Graham Cameron_1]

nohup EXECUTABLE
-- Graham

[Mark Grant]

I imagine that if you had a wrapper script as your omniback postexec command that ran the real script in the background you'd be OK.

omnibackpostexec script would do soemthing like this


nohup script2 &
exit 0

If you really want to go mad you need to fork and exit and for that, lets do perl.

Your omniback post exec script would look like

#!/usr/bin/perl

$PID=fork;
if($pid != 0){
exit 0;
}

`/my/shell/script/here`;



Of course, if you fancy doing your script in perl, then you don't need to run that shell script at the bottom.

[Kevin_31]

Elmar & Graham, tried it but no success.
Mark, tried the first suggestion, still no-go. I'd be interested in trying a fork in shell script, but don't really wanna use perl.

[Mark Grant]

Kevin,

I don't think you can "fork" in a shell but A.Clay Stephenson is dropping his scripting bombs again today so he may well prove me wrong!

Your problem is not the second command (though if it were written correctly you wouldn't have this problem) but the shell that is running it. This is why I can't quite understand why the first option I suggested doesn't work.

However, that perl thing will do nicely as an omniback post exec script (I do something similar myself) and you'll never have to touch perl aain if you didn't want to :)

[Massimo Bianchi]

much, much simpler...

nohup (EXECUTABLE << EOF

EOF) &


Massimo

[Kevin_31]

EXECUTABLE: Syntax error at line 1 : `(' is not expected.

[Kevin_31]

this program must be way-dodgy. I've wrapped up the program and flags/parameters into one script, executed it within another one, using Massimo's suggestion, but still it's a no-go.

Thanks everyone. Maybe i'll try the perl option afterall... back soon.

[Massimo Bianchi]

Let's tear away the parentesis:

####################
EXECUTABLE:

#!/sbin/sh

do_something << EOF

EOF

#######################


nohup EXECUTABLE &



Massimo

[Graham Cameron_1]

Suspect your program does a close(0) and then opens another fd for reading.

Unless you know which fd this is, or have the patience to keep trying

nohup EXECUTABLE 3nohup EXECUTABLE 4
etc up to 20,

then I'd give up if I were you...

-- Graham

[BIHAN]

mkfifo fifo
nohup EXECUTABLE echo "^M" >fifo

[BIHAN]

missing an & at the end of the nohup line

i think
echo > fifo
would be better than
echo "^M" >fifo

[James Lynch]

Kevin,

How about posting this script so that we can have a look at it?

JL

[Kevin_31]

The real issue is the EXECUTABLE, which is part of Oracle Applications 11i Server, and is over 6 megabytes in size. Probably not the best idea to post (I expect it wouldn't run without the other bits of code that make up the Oracle installation.

Thanks everyone, but I think I'll just have to use cron to restart this bit and keep it out of Omniback post-exec alltogether.

cheers

[Mark Ellzey · Accepted solution]

Kevin,

If you are just trying to answer a prompt that the application requires, and it's a carriage return, I've done it as such:
echo "\013" | APPLICATION > /dev/null 2>&1 &

This works for me in a script that runs an Informix backup procedure, which is normally interactive.

Regards,
Mark

[Kevin_31]

Amazing, I've tried every suggestion listed above, and the last one... finally... worked!

cheers Mark!

(I can always count on ITRC Geniuses)

[Todd McDaniel_1]

No points here...

I just want to say I enjoyed reading this puzzle...

We need more posts like this to test our brains power.

I personally troll the boards to educate myself... and posts like this are helping.

[Ulrich Deiters]

... sorry to be late due to my timezone! A useful trick to communicate with a background process works like this:

1st: You start the background job:
bgjob 2>&1 1>logfile |&

2nd: You retrieve the background job's stderr output (error messages, prompts, etc.):
read -p $bg_output

3rd: You send data to the background job's stdin:
bg_input="some_input"
print -p -R $bg_input

This works with POSIX-compatible shells, e.g., /usr/bin/sh and /usr/bin/ksh, but not with bash.

I hope this is useful for you.