Simple CGI Script in Python

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The Python documentation is a pretty good place to start: http://docs.python.org/library/cgi.html

Check List

  1. the scripts starts with:
  #!/usr/bin/env python
  #-*- coding:utf-8 -*-
  1. also import and enable cgi traceback
import cgitb;
cgitb.enable()
  1. the filename ends with .cgi
  2. chmod 755 the_file.cgi
  3. print the headers
 print "Content-Type: text/html; charset=utf-8"     # HTML is following
 print                               # blank line, end of headers
  1. the script is here http://pzwart3.wdka.hro.nl/~yourname/cgi-bin/the_file.cgi

Hello world

#!/usr/bin/env python
#-*- coding:utf-8 -*-
print "Content-Type: text/html"     # HTML is following
print                               # blank line, end of headers
print "Hello!"

Show Headers

HTTP headers are simply environment variables. Use the os.environ dictionary to get at them.

#!/usr/bin/env python
#-*- coding:utf-8 -*-

import os

print "Content-type: text/html"
print

# show all headers as an HTML definition list

print "<dl>"
for key in os.environ:
    print "<dt>" + key + "</dt>"
    print "<dd>" + os.environ[key] + "</dd>"
print "</dl>"


"Discriminating" Response based on IP Address

Interesting headers:

  • HTTP_USER_AGENT (string identifying the user's browser, also often includes information about the computer / operating system as well)
  • REMOTE_ADDR (the IP address of the user's machine *or* gateway)
  • REQUEST_METHOD (either "GET" or "POST")
  • QUERY_STRING (the stuff after the '?' in the users's request URL)
  • HTTP_ACCEPT_LANGUAGE (language code set by user's browser)
#!/usr/bin/env python
#-*- coding:utf-8 -*-

import os

print "Content-type: text/html"
print

addr = os.environ['REMOTE_ADDR']
last = addr.split(".")[-1]
agent = os.environ.get("HTTP_USER_AGENT")

if agent == None:
    print "Go away, bot!"

if (last == "188") or (last=="18") or (last=="67"):
    print '<img src="http://www.kuliniewicz.org/hotlink/hotlink.png" />'
else:
    print 'Hello "%s"' % agent