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Accepted
Eytan
Asked: 2012-03-12 10:30:17 +0800 CST

expect + how to identify if expect break because time out?

  • 772

The target of the following simple expect script is to get the hostname name on the remote machine

Sometimes expect script fail to perform ssh to $IP_ADDRESS ( because remote machine not active , etc )

so in this case the expect script will break after 10 second (timeout 10) , this is OK but......

There are two options

  1. Expect script perform ssh successfully , and performed the command hostname on the remote machine
  2. Expect script break because timeout was 10 seconds

On both cases expect will exit

  • in case of ssh successfully expect will break after 0.5-1 second but in case of bad ssh then it will break after 10 seconds

but I don’t know if expect script perform ssh successfully or not?

is it possible to identify timeout process ? or to verify that expect ended because timeout?

Remark my Linux machine version - red-hat 5.1

Expect script

 [TestLinux]# get_host_name_on_remote_machine=`cat << EOF
  > set timeout 10
  > spawn  ssh   $IP_ADDRESS
  >            expect {
  >                      ")?"   { send "yes\r"  ; exp_continue  }
  > 
  >                      word:  {send $PASS\r}
  >                   }
  > expect >  {send "hostname\r"}
  > expect >    {send exit\r}
  > expect eof
  > EOF`

Example in case we not have connection to the remote host

 [TestLinux]# expect -c  "$get_host_name_on_remote_machine"
 spawn ssh 10.17.180.23
 [TestLinux]# echo $?
 0
linux ksh tcl shell-scripting expect

2 Answers

  1. Best Answer

    you can expect timeout, some version require -timeout just like -regex to test for the invocation of timeout.

    you're expect statement could become

    expect {
    ")?"    { send "yes\r"  ; exp_continue  }
    word:   { send $PASS\r}
    timeout { puts "failed to SSH" }
       }
    • 2

  2. I know this isn't exactly what you asked, but I'd like to offer an alternative. Use ssh keys instead of passwords and bash scripting instead of Expect:

    output=$(ssh -o ConnectTimeout=10 -o BatchMode=yes -o StrictHostKeyChecking=no $IP_ADDRESS "hostname")

if [ $? -eq 255 ]; then
    # Some error occured while attempting to connect.
else
    # Success!
fi

    This doesn't explicitly tell you there was a timeout vs. failed to log in with a private key, etc., but it beats writing Expect.

    • 0