Bash Sort By Column

Sometimes you may want to sort the result of a command, or contents of a file, or even command line input in Linux. The sort command allows you to do all these three things at one go. It allows you to sort values and columns in ascending, descending or even custom order. Also, it does not modify the original input but only the output. This command is available in almost every linux distribution and part of most shells, not just bash shell.

Bash Sort By Column

Here is the syntax for sort command.

sort [options] input

You may change the sort order using various options. By default, sort command

Sorts alphabets in ascending order
Numbers are sorted before alphabets
Lowercase letters have more precedence than uppercase letters

Here are the most commonly used options available for sort command.

-n – sorts in numerical values
-h – compare human-readable numbers such as 1k, 1G
-R – random sort order but group the identical keys
-r – reverse sort (descending order).
-o – save output to file
-u – show unique values
-k – sort data by specific key/column

Now we will look at some common use cases to sort values in bash shell.

1. How to Sort Numerical Values in bash

Let us say you have the following file that contains numbers

$ cat data.txt
34343
334343
232323
232
32124
21
576767

Here is the command to sort the data numerically.

$ sort -n data.txt
21
232
32124
34343
232323
334343
576767

2. How to Sort in Reverse Order

If you want to sort the above data in reverse order, just use -r option

$ sort -r data.txt
576767
34343
334343
32124
232323
232
21

Let us say you have the following file with alphanumeric values.

$ cat data1.txt
34eejnj
eredsffe
33r
ffeff
f3f4ff
fdgfvv
hgjhgh

Here is how to reverse sort the values above.

$ sort -r data1.txt
hgjhgh
ffeff
fdgfvv
f3f4ff
eredsffe
34eejnj
33r

In the above example, sort command outputs all lines starting with alphabets before those starting with numbers. Among them, it displays lines beginning with alphabets in descending order of alphabets, and then displays all lines beginning with numbers in descending.

3. How to Sort by Column in Bash

Sort command allows you to sort data by column using -k option. Let us say you have the following file.

$ cat data2.txt
3 abc 943
2 def 234
1 xyz 178

If you want to sort the data by 3rd column, you need to specify 3 after -k option as shown below.

$ sort -k 3 data2.txt
1 xyz 178
2 def 234
3 abc 943

Please note, the columns are numbered from 1, starting from the leftmost column. The next column is 2, next one is 3 and so on.

4. Save sort output to file

You may also save the sorted output to another or same file with -o command. Just mention the file path to which the sort command’s output needs to be stored after the -o option and before the file to be sorted.

$ sort -o new_data.txt data.txt
$ cat new_data.txt
21
232
232323
32124
334343
34343
576767

Please note, if you don’t specify the full file path in any of the above commands, sort command will look for the file in your present working directory. Also, is you want to modify the input file, just mention it after -o option.

$ sort -o data.txt data.txt
$ cat data.txt
21
232
232323
32124
334343
34343
576767

5. Sort Command output

You may also pass the output of commands to sort command using | (pipe) operator, as shown below. In this example, we reverse sort the output of ls command using sort.

$ ls
abc.txt  conf  data.txt  data1.txt  data2.txt  gpush.sh  logo-transparent.png  mysql_backup.sh  new_data.txt  postit.sh  remove-old-snaps  t  tweet.py  tweet_list

$ ls | sort -r
tweet_list
tweet.py
t
remove-old-snaps
postit.sh
new_data.txt
mysql_backup.sh
logo-transparent.png
gpush.sh
data2.txt
data1.txt
data.txt
conf
abc.txt

The difference between sorting a file vs sorting a command output is that when you sort command output, you need to mention sort command after the command whose output you want to sort. In this case, we mention sort command after ls command and not the other way round. In case of sorting files, we mention sort keyword first, followed by filename.

Bash Sort By Column