Mixing Expect and BASH

Question

I have written a small Expect script to log into a Cisco device; once logged in I want to repeatedly run a command and grep the output.

#!/usr/bin/expect

send_user "Device name: "
expect_user -re "(.*)\n"
set host $expect_out(1,string)

send_user "Username: "
expect_user -re "(.*)\n"
set user $expect_out(1,string)

stty -echo
send_user -- "Password: "
expect_user -re "(.*)\n"
set pass $expect_out(1,string)
stty echo

send_user "show int "
expect_user  -re "(.*)\n"
set intf $expect_out(1,string)
send_user "\n"

spawn telnet $host
expect "Username:"
send "$user\r"
expect "Password:"
send "$pass\r"
expect ">"

At this point we have logged into the device, I want to execute the command "show int xxx" repeatedly and grep the output for a specific line. grep isn't in Expect, nor a command like sleep, so I can loop round executing the show int command, grepping out my specific line. How can I mix Expect and Bash like this?

UPDATE: I've pretty much done the script now, I'll post the full script once I get over this last hurdle. A line set bytesnow [exec grep "packets input" \< showint | cut -d \ -f 9] is throwing the error;

child process exited abnormally
   while executing
"exec grep "packets input" < \showint | cut -d \  -f 9"

But it works fine in a test script I wrote. The file ./showint is there, running that command on the command line works fine? I can't work out what's wrong?

UPDATE: More investigation (http://wiki.tcl.tk/8489) has shown me that the grep exits with status code 1, which means no pattern matches were found, put the command works just fine from the command line? Even with /full/path/to/showint.

END: I fixed my mistake by realising what a fool I had been, answered below. Thanks all for your help :D

Answer 1

This is my first Expect script, its purpose is to give the live (almost, 1 second!) throughput of an interface. The below example gives an interface input speed, because we grep for the line containing "packets input". Change this to "packets output" to get a live output rate for that interface.

#!/usr/bin/expect

# Long delay for those tricky hostnames

set timeout 60

# Prompt user for device name/IP, username, password, 
# and interface to query (gi0/2)

send_user "Device name: "
expect_user -re "(.*)\n"
set host $expect_out(1,string)

send_user "Username: "
expect_user -re "(.*)\n"
set user $expect_out(1,string)

stty -echo
send_user "Password: "
expect_user -re "(.*)\n"
set pass $expect_out(1,string)
send_user "\n"
stty echo

send_user "show int "
expect_user  -re "(.*)\n"
set intf $expect_out(1,string)
send_user "\n"

spawn telnet $host
expect "Username:"
send "$user\r"
expect "Password:"
send "$pass\r"
expect ">"

set byteslast 0
set bytesnow 0

log_user 0

# Enter a continuous loop grabbing the number of bytes that
# have passed through an interface, each second.
# The different in this number each cycle, is essentially
# how much traffic this interface is pushing.

while { true } {
  send "show int $intf\r"
  expect ">"

  set showint [open "showint" "w"]
  puts $showint $expect_out(buffer)
  close $showint

  set bytesnow [exec grep "packets input" \< showint | cut -d \  -f 9]

  if { $bytesnow > $byteslast } {
    set diff [expr $bytesnow - $byteslast]
    set bps [exec expr "$diff" \* 8]
    set kbps [exec expr "$bps" \/ 1000]
  } elseif { $bytesnow < $byteslast } {
    set diff [expr $byteslast - $bytesnow]
    set bps [exec expr "$diff" \* 8]
    set kbps [exec expr "$bps" \/ 1000]
  } elseif { $bytesnow == $byteslast } {
    set kbps 0
  }

  set byteslast $bytesnow
  puts "$kbps Kbps\r"

  sleep 1
}

As this is my first Expect script, I have no doubt it could be written more efficiently and clearly (that always the case I find), so if anyone has any pointers on this one I'm all ears! :)

My problem with my exec grep command turned out to be that prior to that, the file I had opened "showint", I hadn't closed, and I was trying to access another file; school boy mistake!

Answer 2

This is what I would do

log_user 0
while(1) {
  send -- "sh int $intf | i packets input\r"
  set timeout 5
  expect {
    -re "^ +(\d+) packets" { send_user -- "$expect_out(1,string)" }
    timeout { send_user "broke?\n" }
  }
}

That'll get you the number of packets input.