Nrthugu

I am struggling when writing regular expression in python.
For instance I get the following right

"GET /images/launch-logo.gif HTTP/1.0" 220 1839

is matched by

"(S+) (S+)s*(S*)" (d{3}) (S+)

however I still need to include the following cases all together

1. "GET /history/history.html hqpao/hqpao_home.html
HTTP/1.0" 200 1502


2. "GET /shuttle/missions/missions.html Shuttle Launches from
Kennedy Space Center HTTP/1.0"200 8677


3. "GET /finger @net.com HTTP/1.0"404 -

obviously I should change the bold part of the expression

"(S+) (S+)s*(S*)" (d{3}) (S+)

But how should I change it. I have one approach in mind which is change the bold part to

[s |(s*)(S+) |(S+)(12) |(S+)]

where the 2nd, 3rd , 4th expression is the (1), (2), (3) extra cases I need to deal with.

But my expression do not work. What do I misunderstand about regular expression as I simply deal with it case by case.

This Might be a bit messy but it works:

"(S+) (S+[sw.@]*)s*(S*)"s?(d{3})s(S+)*

You can play with it on Regexr. Regexr Shared Link

You may use

^"([^s"]+)s+([^s"]+)(?:s+([^"]+?))?s+([A-Z]+/d[d.]*)"s*(d{3})s*(S+)$

See the regex demo

Details

• 
  ^ - start of a line (use re.M if you are reading the whole file into a variable, f.read())


• 
  " - a double quotation mark


• 
  ([^s"]+) - Group 1: one or more chars other than whitespace and a double quotation mark


• 
  s+ - 1+ whitespaces


• 
  ([^s"]+) - Group 2: one or more chars other than whitespace and a double quotation mark


• 
  (?:s+([^"]+?))? - an optional non-capturing group matching
  
  
  
  
  • 
    s+ - 1+ whitespaces
  
  
  • 
    ([^"]+?) - Group 3: any 1 or more chars other than ", as few as possible
  
  
  
  


• 
  s+ - 1+ whitespaces


• 
  ([A-Z]+/d[d.]*) - Group 4: 1+ uppercase letters, / and then 1 digit followed with any 0+ digits or . chars


• 
  " - a double quotation mark


• 
  s+ - 0+ whitespaces


• 
  (d{3}) - Group 5: three digits


• 
  s* - 0+ whitespaces


• 
  (S+) - 1 or more non-whitespace chars


• 
  $ - end of string.