bash Cookbook

Sorting Numbers

Problem

When sorting numeric data you notice that the order doesn’t seem right:

$ sort somedata
2
200
21
250
$

Solution

You need to tell sort that the data should be sorted as numbers. Specify a numeric sort with the -n option:

$ sort -n somedata
2
21
200
250
$

Discussion

There is nothing wrong with the original (if odd) sort order if you realize that it is an alphabetic sort on the data (i.e., 21 comes after 200 because 1 comes after 0 in an alphabetic sort). Of course, what you probably want is numeric ordering, so you need to use the -n option.

sort -rn can be very handy in giving you a descending frequency list of something when combined with uniq -c. For example, let’s display the most popular shells on this system:

$ cut -d':' -f7 /etc/passwd | sort | uniq -c | sort -rn
     20 /bin/sh
     10 /bin/false
      2 /bin/bash
      1 /bin/sync

cut -d':' -f7 /etc/passwd isolates the shell from the /etc/passwd file. Then we have to do an initial sort so that uniq will work. uniq -c counts consecutive, duplicate lines, which is why we need the pre-sort. Then sort -rn gives us a reverse, numerical sort, with the most popular shell at the top.

If you don’t need to count the occurrences and just want a unique list of values—i.e., if you want sort to remove duplicates—then you can use the -u option on the sort command (and omit the uniq command). So to find just the list of different shells on this system:

cut -d':' -f7 /etc/passwd | sort -u

See Also

• man sort

• man uniq

• man cut