Problems scripting screen

[Nelgin]

I'm having a problem that I hope someone can assist with.

I am running a script to start a number of screen sessions

for i in `cat serverlist
do
screen -d -m -S $i ssh $i
done

We have the systems setup so we can ssh without a passkey, so I get a number of screens.

Now, say I want to stuff a command..

screen -S machine1 -X stuff "who^J"

This works. However if I put it in for a for look

for i in `cat serverlist`
do
screen -S $i -X stuff "who^J"
done

It doesn't. Nothing gets sent to the screen sessions at all.

Anyone have a solution for this?

Thanks,
Nigel

[Micah Cowan]

Nelgin wrote:

> Now, say I want to stuff a command..
>
> screen -S machine1 -X stuff "who^J"
>
> This works. However if I put it in for a for look
>
> for i in `cat serverlist`
> do
> screen -S $i -X stuff "who^J"
> done

The most obvious explanation is that your for-loop isn't doing what you
think it's doing. Screen of course can't possibly know whether or not
it's being invoked as part of a for-loop, or a direct command: given the
same command arguments and the same environment (and sessions state), it
will behave the same way every time.

Knowing this, you should investigate how your for loop is behaving with
respect to how you expect it to behave. Perhaps the very act of running
from a script versus typing directly on a console introduces an
environmental change (fairly unlikely, but worth confriming). Perhaps
the values in "serverlist" aren't what you expect them to be, or the
file's not in the current working directory. Try placing an "echo" line,
or invoke the script using sh's -x option for explanations of how the
shell is evaluating your code.

--
HTH,
Micah J. Cowan
Programmer, musician, typesetting enthusiast, gamer.
Maintainer of GNU Wget and GNU Teseq
http://micah.cowan.name/


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[clemens fischer-3]

On Fri-2009/06/26-18:34 Nelgin wrote:

> screen -S machine1 -X stuff "who^J"
>
> This works. However if I put it in for a for look
>
> for i in `cat serverlist`
> do
> screen -S $i -X stuff "who^J"
> done
>
> It doesn't. Nothing gets sent to the screen sessions at all.

I'd write:  >>screen -S "$i" -X stuff "who^J"<<, ie. quote the variable
as well.  But for testing, try >>echo screen -S "$i" -X stuff "who^J"<<.

This will show the command as the shell sees it.  Is the "^J" a literal
newline or the two characters "^" and "J" in both cases?


clemens, being late, he knows.



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[Gerald Young]

On Saturday 03 October 2009 11:34:32 clemens fischer wrote:
> Is the "^J" a literal newline or the two characters
> "^" and "J" in both cases?

Screen itself interprets the two characters "^" and "J" as a newline.  So type
the command with the two characters, and when the "stuff" command is executed
those characters are replaced by a newline.

Gerald Young


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