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Find which log files contain or don't contain a specific error message

 $ for i in *.log; do grep OutOfMemo $i >/dev/null && echo $i oom || echo $i ok; done

— by Janos on Sept. 13, 2013, 3:43 p.m.

Explanation

In this example I was looking for a list of log files which contain or don't contain a stack trace of OutOfMemoryError events.

  • for i in *.log is to loop over the list of files.
  • For each file, I run grep, but redirect the output to /dev/null, as I don't need that, I just want to see a "yes or no" kind of summary for each file
  • grep exits with success if it found any matching lines, otherwise with failure. Using the pattern cmd && success || failure, I echo the filename and the text "oom" in case of a match, or "ok" otherwise

Remarks:

  • Using grep -q is equivalent to redirecting output to /dev/null, but might not be supported in all systems
  • grep -l can be used to list files with matches, and grep -L to list files without matches, but the latter does not exist in some implementations of grep, such as BSD
  • I realized it a bit late, but grep -c shows a count of the matches, so actually it could have been a suitable and simpler solution