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What are the best ways to search in logs?

In any kind of service what are the best ways to search in the logs for the following cases :

1 - If the bug has already occurred.
2 - If the bug is reproduced and one wants to catch the exception/error occurred.

Some of the ways that i know but inefficient are :

tail -f production.log => log flows and you have to check manually.
tail -n1000 production.log => log for last 1000 lines
tail -f production.log | grep '500 Internal Server Error' => shows the flow of log for only one particular line that says 500.

I want to print for the 100 lines above the log so to print backtrace also in both the cases(especially for second).

Solution

  • You can use sed , i.e.:

    sed  '/500 Internal Server Error/!d' sederror.log|sed 10q

    Explanation:

    sed  '/500 Internal Server Error/!d'

    Will print only lines matching 500 Internal Server Error 

    sed 100q

    Displays the first 100 lines (emulates tail -n 100)