How can I search through an Expect variable - tcl

Question

I'm working on an expect script that connects to a switch and then shows the configuration for an interface. I then analyze this output to check for certain things. I would like to store the output of one of the things that I'm checking, which I'm trying to accomplish by searching through $expect_out(buffer), although I'm having a difficult time finding out how to do this.
How should I go about doing this?
The script looks like the following (cut out unnecessary stuff):
send "show running-config interface $intf\r"
log_user 0
expect "#"
if {[string match "*service-policy input Access-Port*" $expect_out(buffer)]} {
set servicepolicy "yes"
} else {
set servicepolicy "no"
}
if {[string match "*mls qos trust dscp*" $expect_out(buffer)]} {
set mlsqos "yes"
} else {
set mlsqos "no"
}
if {[string matc "*Description*" $expect_out(buffer)]} {
EXTRACT DESCRIPTION STRING FROM $expect_out(buffer)
}
This is what the output of $expect_out(buffer) would typically look like:
Current configuration : 559 bytes
!
interface GigabitEthernet1/0/17
description blablabla
switchport mode access
switchport voice vlan xxxxx
no logging event link-status
authentication event fail retry 0 action authorize vlan xxxxx
authentication event no-response action authorize vlan xxxxx
authentication host-mode multi-domain
authentication port-control auto
authentication violation restrict
mab
no snmp trap link-status
dot1x pae authenticator
dot1x timeout tx-period 5
dot1x timeout supp-timeout 10
no mdix auto
spanning-tree portfast
service-policy input Access-Port
end
The "EXTRACT DESCRIPTION STRING FROM $expect_out(buffer)" line is the part that I am trying to figure out. I know how to split the line up to grab just the description, but i just do not know how to extract the line itself from the buffer variable.

Answer 1

Use the regexp command with the -line option:
% regexp -line {^\s*description (.*)$} $expect(buffer) -> desc
1
% puts $desc
blablabla
I assume the description is not multi-line.
Also, if you just need a boolean value,
set servicepolicy [string match "*service-policy input Access-Port*" $expect_out(buffer)]
or, do this
set servicepolicy [expr {[string match "*service-policy input Access-Port*" $expect_out(buffer)] ? "yes" : "no"}]