Regular expression to match error and associated few lines
I am looking for a single line regular expression to match the word "Error" from the log file and i need to get the few lines above and below the lines that has the word "Error" for debugging purpose.
For example: I need to match for the word " TypeError " and get other few lines above and below this matched lines. atleast i need next 10 lines. Could anyone please help on this ?
Log File content below =>
TypeError : Parameter 'url' must be a string, not undefined at Url.parse (url.js:107:11) at urlParse (url.js:101:5) at Object.urlResolve [as resolve] (url.js:404:10) at parseMarkdown (/opt/controllers/api/userguide.js:53:19) at /opt/controllers/api/userguide.js:33:17 at Object. (/opt/models/api.js:172:4) at /opt/lib/data/api.js:138:5 at IncomingMessage. (/opt/node_modules/httpunch/lib/_wrap_request.js:100:9) at IncomingMessage.g (events.js:180:16) at IncomingMessage.emit (events.js:117:20)
Try this (Fetches upto 10 preceding and succeeding lines)-
(?:(?:.*n){0,10}).*?Error.*(?:(?:n.*){0,10})
Demo
EDIT
Just read the comment about unix environment.
You can use Grep command using the same regex as above.
Like this -
$ grep -Pzo "(?:(?:.*n){0,10}).*?Error.*(?:(?:n.*){0,10})" <filename>
All credits to Kamehameha for this answer, it's based on his regexp, but I went ahead and made it a little bit simpler to follow with an accompanying explanation. It is not as perfect as the original though, but works pretty well.
Full expression
(n.*){0,10}(.*Error:.*)(n.*){0,10}
View on regexr
Match the error line itself
.*Error:.*
This line is actually quite simple. The only thing you need to know is that .* matches any number of characters (but not line breaks). So this line means "Find anything followed by "Error:" followed by anything"
Match any line
n.*
This is also pretty easy to understand: n (newline) followed by anything.
Match up to 10 lines
(n.*){0,10}
This takes the "full line" regex and applies it between 0 and 10 times, as many as possible (since regex is greedy by default).
Putting it all together
What we want is "10 lines + error line + 10 lines", so we just take what we made previously and put into one big statement.
(n.*){0,10}(.*Error:.*)(n.*){0,10}
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