bash Cookbook

Sorting IP Addresses

Problem

You want to sort a list of numeric IP address, but you’d like to sort by the last portion of the number or by the entire address logically.

Solution

To sort by the last octet only (old syntax):

$ sort -t. -n +3.0 ipaddr.list
10.0.0.2
192.168.0.2
192.168.0.4
10.0.0.5
192.168.0.12
10.0.0.20
$

To sort the entire address as you would expect (POSIX syntax):

$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n ipaddr.list
10.0.0.2
10.0.0.5
10.0.0.20
192.168.0.2
192.168.0.4
192.168.0.12
$

Discussion

We know this is numeric data, so we use the -n option. The -t option indicates the character to use as a separator between fields (in our case, a period) so that we can also specify which fields to sort first. In the first example, we start sorting with the third field (zero-based) from the left, and the very first character (again, zero-based) of that field, so +3.0.

In the second example, we used the new POSIX specification instead of the traditional (but obsolete) +pos1 -pos2 method. Unlike the older method, it is not zero-based, so fields start at 1.

$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n ipaddr.list

Wow, that’s ugly. Here it is in the old format: sort -t. +0n -1 +1n -2 +2n -3 +3n -4, which is just as bad.

Using -t. to define the field delimiter is the same, but the sort-key fields are given quite differently. In this case, -k 1,1n means “start sorting at the beginning of field one (1) and (,) stop sorting at the end of field one (1) and do a numerical sort (n). Once you get ...