Using expect to SSH to server and execute commands

Question

I want to write a generic expect script to login through SSH to a system and execute some commands. An example I found had the following:

#!/usr/bin/expect

set fid [open ./.secret]
set password [read $fid]
close $fid
spawn /usr/bin/ssh root@[lindex $argv 0]
expect {
  -re ".*Are.*.*yes.*no.*" {
    send "yes\n"
    exp_continue
    #look for the password prompt
  }

  "*?assword:*" {
    send $password
    send "\n"
  }
}

send -- "PS1='>'\r"
expect -re ">$" { send "hostname\r" }
expect -re ">$" { send "pwd\r" }

...the script seems to login properly but it didn't execute the last 2 sends. Ideas?

Edit: After enabling exp_internal, I noticed the following:

expect: does "" (spawn_id exp4) match glob pattern "*"? yes
expect: set expect_out(0,string) ""
expect: set expect_out(spawn_id) "exp4"
expect: set expect_out(buffer) ""
send: sending "PS1='>'\r" to { exp4 }
Gate keeper glob pattern for '>$' is '>'. Activating booster.

expect: does "" (spawn_id exp4) match regular expression ">$"? Gate ">"? gate=no


expect: does "\r\n" (spawn_id exp4) match regular expression ">$"? Gate ">"? gate=no
Last login: Tue Nov  6 14:13:31 2012 from 1.x.x.x

expect: does "\r\nLast login: Tue Nov  6 14:13:31 2012 from 1.x.x.x\r\r\n" (spawn_id exp4) match regular expression ">$"? Gate ">"? gate=no

I'm trying to send PS1='>'\r because I want to override the prompt. I don't think there's any way for me to predict what the prompt will be and therefore, I wouldn't know what pattern to expect. From the above, it looks like the prompt wasn't changed. How do you tackle a problem like this?

It may be you're sending the prompt configuration too quickly. Take Donal's advice, or use exp_internal 1 (not sure exactly the difference between the 2 commands). — glenn jackman
– glenn jackman, Commented Oct 23, 2012 at 22:55
From the "NEWS" file: -- The old "debug" command (which describes what Expect is doing internally) was renamed "exp_internal". "debug" (and "exp_debug") now invoke the interactive debugger. I tried it and it is indeed interactive, breaking after each step and allowing you to issue expect commands. I found it useful while debugging some regex. Handy but in general, I find exp_internal more handy. — harperville
– harperville, Commented Sep 11, 2013 at 16:33

Donal Fellows · Accepted Answer · 2012-10-23 20:57:34Z

1

There doesn't appear to be anything obviously wrong with your script (though using a different prompt might make matching a bit easier). Which means it is something subtle. I suggest adding this:

exp_debug 1

to somewhere early in your script. It will make the Expect engine print a lot more about what it is doing, which will (probably) help you understand what is going wrong, or failing that help the people here help you…

answered Oct 23, 2012 at 20:57

Donal Fellows

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