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Network (TCP) client in Tcl

Posted by admin (Graham Ellis), 21 November 2002
I had a request on this week's course for a demo program in Tcl that visits a web site, picks up a page from that web site,  and analyses what it gets back.

OK ... here's a program that connects to www.ecb.int (which I have manually resolved to 193.96.201.13), grabs a page that contains a daily table of exchange rates between the Euro and about 30 other currencies, extracts the rate between the pound an Euro, and prints out the result:

Code:
#!/usr/bin/tcl

set sock [socket 193.96.201.13 80]

puts $sock "GET /home/eurofxref.htm HTTP/1.0\n"
flush $sock

while {[gets $sock line] >= 0} {
       append page $line
       }

regexp {>GBP<.*?>\s*<.*?>(.*?)<.*?>\s*<.*?>(.*?)<} $page all name rate

puts "Exchange rate to GBP ($name) from Euros is $rate"


Yep, it's that short!  And run, we get ....

Code:
$ ./exrate.tcl
Exchange rate to GBP (Pound sterling) from Euros is 0.63640
$


Footnote - the European Central Bank updates its exchange rates tables each afternoon, and declares on its website that this information is being placed in the public domain so you're free to use it too.  If you're going to use it many times per day, do the ECB the courtesty of grabbing a copy just once each time they update it, and cache the HTML on your local machine!






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