True, interacting with a shell reliably is not simple, but neither are many other tasks. It's taken many years of small incremental improvements to get where it is today.

# #!/usr/bin/expect -f (include this file, don't run it)
# Login and logout expect procedures for Cisco SSH or telnet access
# 
# written by Scott L. Miller
#
# Last modified:
# 6/15/2013 By Scott L. Miller
#
######################################################################
+#
# Handle the login & logout procedures 
#
# login will return the prompt string if successful
#
# The calling script expects return codes of 2 or less to mean the
# login was unsuccessful, and 3 or more if at least the login was
# successful but there were other errors.
######################################################################
+#

proc connect_login { hostaddr user } {
    global logfile procid expect_out spawn_id

    set try_telnet 0

    spawn /usr/bin/ssh -l $user $hostaddr

    expect {
        -gl "timeout"                    { puts $logfile "Connection t
+imed out"; exit 1 }
        "timed out"                    { puts $logfile "Connection tim
+ed out"; exit 1 }
        "Connection refused"                { puts $logfile "Connectio
+n refused ssh"; set try_telnet 1 }
        "uthentication failed"                { puts $logfile "SSH Aut
+hentication failed"; exit 1 }
        -re "authenticity of host .* can't be established"    { 
            expect {
                "connecting (yes/no)"        { send "yes\r" }
            }
        }

        "REMOTE HOST IDENTIFICATION HAS CHANGED" {
            expect {
                -re "(Offending key \[^\r]*)" {
                    puts $logfile "Host SSH key has changed, $expect_o
+ut(1,string)";
                }
            }
            exit 1 
        }

        -notransfer "assword:"                { }
        default                        { puts $logfile "expect timed o
+ut ssh"; exit 2 }
    }

    if { $try_telnet > 0 } {
        set pstr [login_telnet $hostaddr $user]
    } else {
        set procid $spawn_id
        catch { login_ssh } pstr
    }

    return $pstr
}

proc login_ssh {} {
    global logfile procid ropwd rwpwd expect_out spawn_id

    #set spawn_id $procid
    expect {
        -gl "timeout"                    { puts $logfile "Connection t
+imed out"; exit 1 }
        "timed out"                    { puts $logfile "Connection tim
+ed out"; exit 1 }
        "Connection refused"                { puts $logfile "Connectio
+n refused"; exit 1 }
        "assword:"                    { send "$ropwd\r" }
        default                        { puts $logfile "expect timed o
+ut ssh login"; exit 2 }
    }

    expect {
        "Permission denied"                { puts $logfile "Login inco
+rrect"; exit 1 }
        "assword:"                    { puts $logfile "Login incorrect
+"; exit 1 }
        #attempt to match empty line between password prompt and cisco
+ command prompt
        #"\r\n\r\n"                    { }
        "\r\n"                        { }
        "available commands.\r\n"            { }
        default                        { puts $logfile "expect timed o
+ut ssh passwd"; exit 2 }
    }

    catch { get_prompt_and_enable } pstr

    return $pstr
}

proc login_telnet { hostaddr user } {
    global logfile ropwd rwpwd expect_out spawn_id

    spawn telnet $hostaddr

    expect {
        "timeout"                    { puts $logfile "Connection timed
+ out"; exit 1 }
        "timed out"                    { puts $logfile "Connection tim
+ed out"; exit 1 }
        "Connection refused"                { puts $logfile "Connectio
+n refused telnet"; exit 1 }
        "sername:"                    { send "$user\r" }
        default                        { puts $logfile "Connection tim
+ed out"; exit 2 }
    }

    set procid $spawn_id

    expect {
        "assword:"                    { send "$ropwd\r" }
        default                        { puts $logfile "expect timed o
+ut waiting for telnet password:"; exit 2 }
    }

    expect {
        "assword:"                    { puts $logfile "Login incorrect
+"; exit 1 }
        "Authentication failed"                { puts $logfile "Login 
+incorrect"; exit 1 }
        -notransfer -re "(>|#)"                { }
        default                        { puts $logfile "expect timed o
+ut after telnet password"; exit 2 }
    }

    catch { get_prompt_and_enable } pstr

    return $pstr
}


proc get_prompt_and_enable {} {
    global logfile procid rwpwd expect_out spawn_id

    expect {
        "assword:"                    { puts $logfile "Login incorrect
+"; exit 1 }
        -re "(\[a-zA-Z0-9_@\\-: ]*)(>|#)"            { 
####        grab the prompt string to simplify prompt recognition & he
+lp eliminate false positives
            set pstr $expect_out(1,string)
            set plvl $expect_out(2,string)

            #yeah, the bare '>' below is correct, but I don't like the
+ way it looks either
            if { [string equal $plvl >] } {  
                send "enable\r"
                expect {
                    "assword:"                    { send "$rwpwd\r" }
                    default                        { puts $logfile "ex
+pect timed out during enable"; exit 2 }
                }

                expect {
                    "Access denied"                    { puts $logfile
+ "Enable Login incorrect"; exit 1 }
                    -notransfer "[set pstr]#"            { } 
                    default                        { puts $logfile "ex
+pect timed out after enable passwd"; exit 2 }
                }
            }
            send "\r"
        }

        default                        { puts $logfile "expect timed o
+ut while identifying prompt string"; exit 2 }
    }

    expect {
        -notransfer "[set pstr]#"            { } 
        default                        { puts $logfile "expect timed o
+ut after enable mode"; exit 3 }
    }

    return $pstr
}
######################################################################
+###
# remember, all the expect pre- and post- tests are still active,
# That's why we need the "global ... " statement
######################################################################
+###
proc logout {} {
    global pstr logfile lastcmd errorcount

    expect_after {
        #The work is done, we're just trying to shutdown cleanly, If t
+his
        #shutdown attempt is ALL that fails, there's no sense in sayin
+g the
        #operations failed. Unless of course the operations did fail..
+.
        default  {
            puts $logfile "expect timed out after \'$lastcmd\', exitin
+g with $errorcount status"
            exit $errorcount
        }
    }

    expect "[set pstr]#"                    { send "exit\r" }

    expect {
        "\r\n"                         { close }
    }

    wait;
}

#
# vim:ai:ts=8:sw=8

[download]
-Scott

In reply to Re^2: Off Topic: Looking for good Expect scripts by 5mi11er
in thread Off Topic: Looking for good Expect scripts by 5mi11er

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