Exploring the logs

As a developers an important part of our job sometimes is to fix problems in the different environments where our applications are deployed. Usually, this means to deal with huge log files to find where errors occur, and their stacktraces to add some context to the problem. The problem is that usually log files are verbose and contain a lot of information.

A couple of useful command to deal with this can be:

  • grep
  • zgrep

Both have the same purpose the only difference it that “grep” works with normal files and “zgrep” works with compressed (.gz) files. Usualy files are compressed due to the logs rotation scheduled in the servers. Both commands have multiple options and flags but, I am going to expose here two flags that have been useful multiple times:

  • -E expr: Allow as to supply a pattern for the search.
  • -C num: Print num lines of leading and trailing output context.
  • –color: Shows the matched information in color in the terminal.

As an example we have:

zgrep --color -E '(Sending email)' myLog.log-20170621.gz
grep --color -E '(Sending email)' myLog.log
grep --color -C 25 -E '(Sending email)' myLog.log

As we can see, obviously, they can be combined.

 

Exploring the logs