Best way to simulate “group by” from bash?

Question

Suppose you have a file that contains IP addresses, one address in each line:

10.0.10.1
10.0.10.1
10.0.10.3
10.0.10.2
10.0.10.1

You need a

Answer 1

The quick and dirty method is as follows:

cat ip_addresses | sort -n | uniq -c

If you need to use the values in bash you can assign the whole command to a bash variable and then loop through the results.

PS

If the sort command is omitted, you will not get the correct results as uniq only looks at successive identical lines.