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Get coprocess output into var

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# 1  
Old 11-05-2008
Question Get coprocess output into var
This is probably a simple one for the wise.

I have just started using a coprocess (first time) in order to facilitate telnet'ing from inside a shell script. It's working, but when I run a remote command I need to get the output into a local variable, but alas my kung-fu is weak.

Code:
#! /usr/bin/ksh                                        |
                                                       |
DELAY=1                                                | <= Sleep delay
UNAME=d269836                                          | <= Login credentials
PWORD=my_password                                      |
SUPWORD=su_password                                    | <= su login credentials (i know i know)
                                                       |
exec 4>&1                                              | <= Make cop output > stdout
telnet mmm2 >&4 2>&4 |&                                | <= Start cop
sleep $DELAY                                           |
print -p $UNAME                                        | <= Login
sleep $DELAY                                           |
print -p $PWORD                                        |
sleep $DELAY                                           |
print -p su -                                          | <= Go su on remote host
sleep $DELAY                                           |
print -p $SUPWORD                                      |
sleep $DELAY                                           |
print -p clear                                         | <= Clear telnet junk from screen
sleep $DELAY                                           |
print -p cO=\$\(/my_command \)\>/dev/null 2\>/dev/null | <= This *will* put the figure into $cO, but I think $cO 
sleep $DELAY                                           |    is local to the telnet session on remote host?
echo $cO                                               | <= Therefore the output from this is nothing.    
sleep $DELAY                                           |

I used the sample supplied by Perderabo to construct this (very handy, props to Perderabo!! => https://www.unix.com/shell-programming-scripting/11359-need-script-passwd-cant-use-expect-tool-3.html#post40791), and I basically understand the idea of coprocesses, but I just can't get succinct output back into a local variable. I have also tried running my_command in background (and not) followed (and preceded) by a "read -p cO" but the read just sits there and halts the script until ^C.


Any takers?
Last edited by dan-e; 11-05-2008 at 06:57 PM.. Reason: bump
# 2  
Old 11-05-2008
Bump! Hardly anyone has even read this... wrong forum?
# 3  
Old 11-05-2008
Tread softly, for you tread on Rule #4.

I have to admit I generally avoid the use of co-processes due to their complexity and the convenient alternatives such as expect (instead of co-processes) and ssh (instead of telnet). Any reason why you particularly need to use them here... a learning exercise? My telnet on HP-UX doesn't seem to want to deal in stdin/stdout/stderr anyway, it seems to talk directly to my tty... I'll try elsewhere too.
# 4  
Old 11-05-2008
oh, oops. Actually I more stomped on it since I also sent a PM to someone in-the-know...

The host script which needs to use this snippet does most of its work with ssh, but one particular remote host does not have ssh (and wont, before this project is due) hence the telnet.

I may be able to try expect; but I'm not sure how it will go logging in + going to su before running my_command on remote host...
# 5  
Old 11-05-2008
I don't know how to make ksh behave the way you want. The best I can come up with is to send a command to the remote system to run a command and put the output in a remote file. Then use ftp to retrieve the file and examine the contents. It's not pretty but it works in environments where freeware is not available.

This stuff is much easier with openssh and that is what I do these days. No complex co-process or exec statements are needed. And it's much more secure.
# 6  
Old 11-05-2008
expect is perfect for all of the above. Consider using autoexpect to record a manual session first and generate a script... which you can then modify to trim out the excessively verbose regex it generates.
# 7  
Old 11-05-2008
Thanks all, I'll try expect/autoexpect and see what I can come up with. Sorry for being pushy... it's a side effect of my stupidity.
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