How to solve this using regex?

Question

Given that string:

\n
\n
text1\n
\ttext2\n
  Message: 1st message\n
some more text\n
\n
\n
  Message: 2dn message\n\n
\t\t
Message: 3rd message\n
text3\n

I want to extract messages from a multiline string (token is 'Message: '). What regex expression should I use to capture those 3 groups:

• group 1 : '1st message'
• group 2 : '2dn message'
• group 3 : '3rd message'

I tried a lot of things but I can get the expression to work because the string is a multiline string.

My program is in python 2.6 but I suppose it does not make a big difference what language I use...

Answer 1

>>> re.findall('Message: (.+?)$', s, re.M)
['1st message', '2dn message', '3rd message']

re.M flag gives special meaning to ^ and $:

When specified, the pattern character '^' matches at the beginning of the string and at the beginning of each line (immediately following each newline); and the pattern character '$' matches at the end of the string and at the end of each line (immediately preceding each newline). By default, '^' matches only at the beginning of the string, and '$' only at the end of the string and immediately before the newline (if any) at the end of the string.

(.+?)$ matches at least one character till the closest end of the string-character.

edit: indeed the simple version will work too:

>>> re.findall('Message: (.+)', s)
['1st message', '2dn message', '3rd message']

I'm surprised it wasn't in the list of those numerous things you tried :)

Answer 2

@OP,you don't need a regex. Assuming you don't care about the lines after "Message:",

for line in mystring.split("\n")
    if "Message:" in line:
         print "found: ",line