[add information about expect's spawn command, pointers to its man page on http://www.tcl.tk/man/ , etc.]
spawn creates a session with a program or remote device that Expect can manage. Spawned sessions can be automated using other Expect commands, such as expect, interact and exp_send.
The man page for spawn is actually part of the Expect man page http://www.tcl.tk/man/expect5.31/expect.1.html .
A very simple example - ping an ip address:
#!/bin/sh
# The next line is executed by /bin/sh, but not tcl \
exec /homes/ashnoc01/noc/rbacon/tcl/ActiveTcl/bin/tclsh8.4 $0 ${1+"$@"}
package require Expect
spawn -noecho /usr/local/bin/nping -c 5 $argv
log_user 0
expect {
"\r" {
puts -nonewline "$expect_out(buffer)"
exp_continue
}
eof {
puts -nonewline "$expect_out(buffer)"
}
}
puts "AutoPing finished\n"
exitOutput:
> AutoPing 62.188.74.130
PING 62.188.74.130: 64 data bytes
EchoReply from 62.188.74.130: len=64 ttl=242 seq=0 time=81.157 ms.
EchoReply from 62.188.74.130: len=64 ttl=242 seq=1 time=80.768 ms.
EchoReply from 62.188.74.130: len=64 ttl=242 seq=2 time=80.709 ms.
EchoReply from 62.188.74.130: len=64 ttl=242 seq=3 time=80.915 ms.
EchoReply from 62.188.74.130: len=64 ttl=242 seq=4 time=80.940 ms.
----62.188.74.130 PING Statistics----
5 transmitted, 5 received, 0.00% packet loss.
round-trip (ms) min/avg/max = 80.709/80.898/81.157
var/sdev/skew/kurt = 0.030/0.174/0.323/1.311
AutoPing finishedescargo 20 Sep 2005 - Let's see if I remember this correctly. A frequently made mistake in Expect is to spawn a new process in a procedure, and then not assign the returned process identifier to anything that gets it out of the proc local scope.
Without the pid to pass to other Expect commands, they won't work as intended. It might also be possible to pass the wrong pid because of the overwriting (or not overwriting) the spawn_id.
RJ 21 Sep 2005 - You remember correctly. An important point. An example of that:
proc connect_server {server} {
spawn -noecho rlogin $server
set sid($server) $spawn_id
return $sid($server)
}
set sid(myserver) [connect_server myserver.org]
set sid(otherserver) [connect_server otherserver.org
expect $sid(myserver) "%"
exp_send "ls -l\r"
expect $sid(otherserver) "%"
exp_send $sid(otherserver) "ls -l\r"
expect $sid(myserver) "%"
set output_from_myserver $expect_out(buffer)
expect $sid(otherserver) "%"
set output_from_otherserver $expect_out(buffer)
....do stuff with the server outputArrays of spawn_ids allow you to connect to multiple servers and hold those connections open indefinitely, switching at will.
escargo - I note that connect_server uses an array, sid, that is not declared as global. Is this one of those cases where variable scoping in expect is different than Tcl? (That is, in this case, expect doesn't find the variable in the local scope so it automatically checks the global scope for it.)
RJ - Nope - Expect does not globalize variables unless told to. It really didn't need to be an array in the proc, just a variable. The return sends it back. But yes, it could have been a global variable - thus negating the need for returning it in the proc. I'm generally very bad at polluting the global namespace, so I try not to when I put up something anyone will actually look at. ;:
That example of using Expect to drive ping is totally unmotivating. You might as well use exec, no? Expect's strength comes from taking control of interactive processes like passwd or telnet.
RJ The example was a request in Ask, and it shall be given #3, placed here to kill the second bird (an example of using spawn).