looping breaks when I call a script with expect in it

frater · 06-24-2009, 07:39 AM

I wrote a script to check cpe's (modems) remotely.
It telnets / ssh's into the cpe gets some parameters and writes them to a file.
This script uses 'expect' and works fine.

After writing this script I wanted to write a script which parses the file with all the cpe-credentials and have them checked with only 1 command. "Quite easy" I thought...

Code:

while read line ; do
   HOST="`echo "${line}" | awk -F\; '{print $1}' | grep "\."`"
   PORT="`echo "${line}" | awk -F\; '{print $3}'`"
   if [ ! -z "${HOST}" ] ; then
     echo -n "\"${HOST}\"," >>/var/run/allcpes
     chkcpe $HOST >>/var/run/allcpes
   fi
done </etc/chkcpe.cpe
echo ""

This script would only call the first modem in the file /etc/chkcpe.cpe.
The script didn't crash because it did execute the 'echo ""'

I did some extensive debugging and it turned out it that it only happened after invoking "expect" within the script "chkcpe"

I didn't want to surrender so I wrote this workaround. It also proofs somehow that there's something tricky going on with expect.

Code:

n=1
while true ; do
   line="`cat /etc/chkcpe.cpe | awk "NR == $i"`"
   let i+=1
   [ -z "$line" ] && exit

   HOST="`echo "${line}" | awk -F\; '{print $1}' | grep "\."`"
   PORT="`echo "${line}" | awk -F\; '{print $3}'`"
   if [ ! -z "${HOST}" ] ; then
     echo -n "\"${HOST}\"," >>/var/run/allcpes
     chkcpe $HOST >>/var/run/allcpes
   fi
done
echo ""

Although I found a solution that works, I'd still like to know why it is doing this. To make it complete... This is the code that breaks it.

Code:

    expect -c "set timeout -1;\
    spawn ssh -o StrictHostKeyChecking=no -p $PORT $HOST -l ${USERNAME} ;\
    match_max 100000;\
    expect *assword:*;\
    send -- ${CREDENTIAL}\r;\
    expect ${WAITFOR}*;\
    send -- get\ WANDevice.\r;\
    expect OK;\
    expect ${WAITFOR}*;\
    send -- get\ DeviceInfo.\r;\
    expect OK;\
    expect ${WAITFOR}*;\
    send -- exit\r;\
    interact;" >$FOUTPUT 2>$FERROR

BTW...
I also tested:
cat /etc/chkcpe.cpe | while read line ; do ; script ; done

frater · 06-24-2009, 10:53 AM

Another thing I noticed with "expect" is that it stops halfway when I run it as a daemon. Anyone noticed this? I did test it on 2 seperate machines (Red Hat Linux 9 and Fedora Core 9)

And more important.....
The cure?

I think both problems have the same cause......

Code:

    expect -c "set timeout -1;\
    spawn ssh -o StrictHostKeyChecking=no -p $PORT $HOST -l ${USERNAME} ;\
    match_max 100000;\
    expect *assword:*;\
    send -- ${CREDENTIAL}\r;\
    expect ${WAITFOR}*;\
    send -- get\ WANDevice.\r;\
    expect OK;\
    expect ${WAITFOR}*;\
    send -- get\ DeviceInfo.\r;\
    expect OK;\
    expect ${WAITFOR}*;\
    send -- exit\r;\
    interact;"

frater · 06-25-2009, 04:20 AM

After I changed the way I was calling expect I was able to use a normal "while read line ; do ; code ; done <file" construct.

In the script I was calling "expect -c "<expect commands>"

I changed this by making a seperate executable file:

Code:

#!/usr/local/bin/expect -f
set HOST [lindex $argv 0]
set PORT [lindex $argv 1]
set USERNAME [lindex $argv 2]
set CREDENTIAL [lindex $argv 3]
set WAITFOR [lindex $argv 4]

set timeout 90
spawn ssh -o StrictHostKeyChecking=no -p $PORT $HOST -l "${USERNAME}"
match_max 100000
expect "*assword:*"
send "${CREDENTIAL}\r"
expect "${WAITFOR}*"
send "get WANDevice.\r"
expect "OK"
expect "${WAITFOR}*"
send "get DeviceInfo.\r"
expect "OK"
expect "${WAITFOR}*"
send "exit\r\r"
expect eof
exit 0

And just invoke that expect-script from within the 2nd bash script.
It then didn't escape the loop...

Daemonizing the command wasn't necessary at all.... I can just set the timeout to a reasonable timespace to be sure it doesn't wait forever.
I also got rid of the "interact" command which I just copy/pasted from an example..
I also prefer to call expect from a file after all.
Less escape characters.....