Count backwards with seq in Linux

Written by Claudio Kuenzler - 0 comments

Published on July 12th 2017 - Listed in Linux

Needed to manually create some basic web statistics using awstats (a one shot statistic). My approach was to get all the rotated logs and create one big access log. I wanted the lines of that access log in the correct order to avoid awstats tumbling.

First I unzipped all rotated logs:

gunzip *gz

Then I needed to get the log entries from rotated file 40 down to rotated file 9. But here's the catch: How do I count down without having to note every single number from 40 to 9 (that would be something like for i in 40 39 38 37, etc)? I know how to automatically count up using seq:

$ seq 1 5
1
2
3
4
5

So I needed to find a way to count backwards. The solution? seq again :-)

seq offers an optional parameter between the starting and the ending number. From the --help output:

$ seq --help
Usage: seq [OPTION]... LAST
  or:  seq [OPTION]... FIRST LAST
  or:  seq [OPTION]... FIRST INCREMENT LAST
Print numbers from FIRST to LAST, in steps of INCREMENT.
[...]

Example: Count up to 10 but increase with 2 numbers:

$ seq 1 2 10
1
3
5
7
9

The INCREMENT number can be negative, too:

$ seq 10 -1 1
10
9
8
7
6
5
4
3
2
1

And this is actually the way to count down. To put together all rotated logs in the correct order, I finally used the following command:

$ for i in $(seq 40 -1 9); do cat access.log.$i >> final.access.log; done

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