Expect : error can't read "ip": no such variable - tcl

Question

I am a newbie in expect / TCL and trying to parse an HTML page that has output some thing like below:
<li><p>Timestamp: Wed, 14 Nov 2012 16:37:50 -0800
<li><p>Your IP address: 202.76.243.10</p></li>
<li><p class="XXX_no_wrap_overflow_hidden">Requested URL: /</p></li>
<li><p>Error reference number: 1003</p></li>
<li><p>Server ID: FL_23F7</p></li>
<li><p>Process ID: PID_1352939870.809-1-428432242</p></li>
<li><p>User-Agent: </p></li>
My script is below. I am able to get the web page which I am not able to parse the line "Your IP address:" which is giving me errors:
#!/usr/bin/expect -f
set timeout -1
spawn telnet www.whatismyip.com 80
send "GET /\r\n"
expect
set output $expect_out(buffer)
foreach line [split $output \n] {
regexp {.*<li><p>Your IP Address Is:.*?(\d+\.\d+\.\d+\.\d+)} $line ip
if {[string length ${ip}]} {
puts $ip
}
}
The error is:
Connection closed by foreign host.
can't read "ip": no such variable
while executing
"string length ${ip}"
("foreach" body line 3)
invoked from within
"foreach line [split $output \n] {
regexp {.*<li><p>Your IP Address Is:.*?(\d+\.\d+\.\d+\.\d+)} $line ip
if {[string length ${ip}]} {
..."
(file "./t4" line 7)
Any pointers where I am doing wrong?

Answer 1

The regular expression did not match, so the variable was not assigned. You should check the result of regexp to see if the match succeeded; when not using the -all option to regexp, you can treat it like a boolean. Try this:
foreach line [split $output \n] {
if {[regexp {<li><p>Your IP Address Is:.*?(\d+\.\d+\.\d+\.\d+)(?!\d)} $line -> ip]} {
puts $ip
}
}
The -> is really a (weird!) variable name which will hold the whole matched string; we're not interested in it (just the parenthetical part) so we use the non-alphabetic to mnemonically say “this is going to there” (the submatch to the ip variable).

Answer 2

Your line contains "address" (lowercase) but you're trying to match "Address" (uppercase). Add the
-nocase option to the regexp command. Also, Tcl regular expressions cannot have mixed greediness -- the first quantifier determines if the whole expression is greedy or non-greedy (I can't find where this is documented right now).
regexp -nocase {IP Address.*(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})} $line -> ip

Answer 3

If your ultimate goal is to get your host's external IP, then go with an API solution, such as one from exip.org:
#!/usr/bin/env tclsh
set api http://api-nyc01.exip.org/?call=ip
if {[catch {exec curl --silent $api} output]} {
puts "Failed to acquire external IP"
} else {
puts "My external IP is $output"
}
Please visit their API site for more information, especially if you live outside the USA. This solution requires curl, which you might need to install.