CODEWITHSUNDEEP
bashgrepcountercatwc
Bas Peeters
Bas Peeters

Reputation: 3354

Keep count of occurrences in a truncating file

Let's say I have a file called data.log.

Data constantly gets appended to it which can contain 'flag' and it gets truncated by an external script:

[13/Jan/2015:11:11:53 +0000] curabitur flag lacinia nibh in feugiat mollis

tail: data.log: file truncated

[13/Jan/2015:11:11:53 +0000] dapibus enim sagittis efficitur

[13/Jan/2015:11:11:54 +0000] iaculis non flag ac urna.

After declaring counter=0, I want to increment it with the amount of found occurrences. I came up with something like this, which uses wc -l to count the lines in data.log containing 'flag':

counter=$(($counter+$(cat data.log | grep s | wc -l)))
echo $counter

Now there's only one problem left: the truncating. How would I approach this? I thought of doing a watch, but how do I pick up on the truncating event? Or is there another direction I should be heading altogether?

Upvotes: 2

Views: 71

Answers (1)

pgl
pgl

Reputation: 8011

This should work for you:

$ tail -F data.log | grep --line-buffered s | while read match ; do ((counter++)) ; done

The -F flag for tail is the same as --follow --retry. --retry is the magic bit here:

   --retry
          keep trying to open a file even when it is or becomes inaccessi‐
          ble; useful when following by name, i.e., with --follow=name

I also used --line-buffered with grep, to avoid the while loop needing to wait for output.

One problem with this that I've just realised: if flag appears more than once for every line, $counter will still only be incremented by 1. But that issue is in your solution as well.

Upvotes: 1

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