How to capture a couple of lines around a regex match?

Question

I am searching for a regex expression to match couple of lines over the matched line. For example:

ABCDEFGHADEFGH
ABCDEFGHADEFGH
ABCDEFGHDEFGHABCDEFGH
ABCDEFGHDEFGHABCDEFGH
ABCDEFGHABCDEFGHABCDEFGH
ABCDEFGHABCDEFGHABCDEFGH
XXXXXXXX

I would like to capture the 2 lines above the XXXXXXXX.

Any help would be appreciated. Note: with Python using library re

Using what software? Different programs have different ideas about what a regexp is. — David Richerby, Apr 11, 2015 at 13:00
If you are using python, it might be better to dump the whole into an array, where each row is its own element. You then loop through the array, finding XXXXXXXX, once found use the index of that item -1 and -2 to get the lines. — LPChip, Apr 11, 2015 at 13:27
hi man thanks for the advice, i did it already with a for loop but wondering how to do with regex — takobaba, Apr 11, 2015 at 14:35

Community · Accepted Answer · 2021-06-15 11:30:48Z

21

The following RegEx tests for a variable amount of lines before the XXXXXXXX line and returns them in the first capture group.

((.*(\n|\r|\r\n)){2})XXXXXXXX

(.*(\n|\r|\r\n)) tests for a string ending with a newline. (\n for Unix, \r for old Mac OS, \r\n\ for Windows)
{2} quantifies this 2 times.
() around that makes sure all lines come in one capture group.
XXXXXXXX is the string that the text has to end with.

Now in Python, you can use p.match(regex)[0] to return the first capture group.

CommunityBot

1

answered Apr 11, 2015 at 14:10

erikgaal

5843 silver badges12 bronze badges

4

Be wary this may cause issues on Windows. If it does, try \r\n instead of just \n.
– Qix - MONICA WAS MISTREATED
Apr 14, 2015 at 20:55
1

Of course, this will match only a line that begins with XXXXXXXX (but it doesn't necessarily end with XXXXXXXX).
– G-Man Says 'Reinstate Monica'
Mar 8, 2020 at 23:52

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Suraj Ravindra Khurana · Accepted Answer · 2020-03-08 22:39:05Z

-1

Adding to erikgaal`s answer, use an extra .* before xxxxxx,to match any tabs/white spaces.

((.*\n){2}).*xxxxxxx

answered Mar 8, 2020 at 22:39

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2

Well, .* won't match just tabs/spaces; it will match anything (e.g., "The quick brown XXXXXXX").
– G-Man Says 'Reinstate Monica'
Mar 8, 2020 at 23:17

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2 Answers 2