Python regex match across multiple lines

Question

I am trying to match a regex pattern across multiple lines. The pattern begins and ends with a substring, both of which must be at the beginning of a line. I can match across lines, but I can't seem to specify that the end pattern must also be at the beginning of a line.

Example string:

Example=N      ; Comment Line One error=

; Comment Line Two.

Desired=

I am trying to match from Example= up to Desired=. This will work if error= is not in the string. However, when it is present I match Example=N ; Comment Line One error=

config_value = 'Example'
pattern = '^{}=(.*?)([A-Za-z]=)'.format(config_value)
match = re.search(pattern, string, re.M | re.DOTALL)

I also tried:

config_value = 'Example'
pattern = '^{}=(.*?)(^[A-Za-z]=)'.format(config_value)
match = re.search(pattern, string, re.M | re.DOTALL)

Wiktor Stribiżew · Accepted Answer · 2018-05-02T14:35:15.373

9

You may use

config_value = 'Example'
pattern=r'(?sm)^{}=(.*?)(?=[\r\n]+\w+=|\Z)'.format(config_value)
match = re.search(pattern, s)
if match:
    print(match.group(1))

See the Python demo.

Pattern details

(?sm) - re.DOTALL and re.M are on
^ - start of a line
Example= - a substring
(.*?) - Group 1: any 0+ chars, as few as possible
(?=[\r\n]+\w+=|\Z) - a positive lookahead that requires the presence of 1+ CR or LF symbols followed with 1 or more word chars followed with a = sign, or end of the string (\Z).

See the regex demo.

edited May 02 '18 at 14:35

answered May 02 '18 at 14:30

Wiktor Stribiżew

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I should probably add this to the question. The second string might not be the word Desired. The second string could be any group of characters A-Za-z followed by =. – 10SecTom May 02 '18 at 14:34
1

@10SecTom Then use `(?=[\r\n]+\w+=|\Z)` lookahead. – Wiktor Stribiżew May 02 '18 at 14:37
Cheers for the help. – 10SecTom May 02 '18 at 14:40
One last question, I ran the code and the groups return from N to just before the Desire=. If i wanted Example= to be within the match also? – 10SecTom May 02 '18 at 14:42
@10SecTom Just get `match.group(0)`, the whole match. And remove the capturing group if you do not need it, i.e. `(.*?)` => `.*?`. – Wiktor Stribiżew May 02 '18 at 14:47
Perfect! Thanks again. – 10SecTom May 02 '18 at 14:55

Python regex match across multiple lines

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