sort command in Linux Explained [with Examples]

The sort command in Linux is a command-line utility used for sorting text files or data streams. Its primary purpose is to arrange lines of text in a more structured and organized manner.

sort can perform a wide range of sorting operations, such as alphabetical or numerical sorting, ascending or descending order, and sorting by specific criteria within each line.

Syntax

The basic syntax for the sort command is as follows:

sort [OPTION]... [FILE]...

Options

Here are some commonly used options:

• -r: Sort in reverse order (descending).
• -n: Sort numerically instead of lexicographically (for numbers).
• -k: Sort by specific fields within each line.
• -b: Ignore leading whitespace when sorting.
• -f: Perform a case-insensitive sort.
• -u: Remove duplicate lines, displaying only unique lines.
• -t: Specify a custom field delimiter.
• -c: Check if a file is already sorted (exit status indicates sorted or not).
• -o: Output to a file instead of displaying on the terminal.
• -M: Sort by month name.
• -h: Sort human-readable numbers (e.g., 1K, 2M) correctly.

sort Command Examples

Sorting in Ascending Order

By default, the sort command sorts lines in ascending order (A to Z or 0 to 9).

Example 1: Sorting from a File

Let's assume we have a file named sampledata.txt with the following content:

Banana 10
Cherry 5
Apple 7
Grapes 2

You can sort it in ascending order with this command:

sort sampledata.txt

Output:

Apple 7
Banana 10
Cherry 5
Grapes 2

This will sort lines in alphabetical order based on the first word in each line.

Example 2: Sorting from Standard Input

You can also provide input to sort via the standard input, which is useful when using pipelines. For example:

echo -e "banana\napple\ncherry" | sort

Sorting in Descending Order

To sort in descending order, where the highest value or latest character comes first, use the -r option.

Example 3: Sorting in Descending Order

sort -r sampledata.txt

Output

Grapes 2
Cherry 5
Banana 10
Apple 7

Sorting Numerically

To sort numerically, you can use the -n option.

Example 4: Numerical Sorting

Suppose we have a file named numbers.txt with the following content:

42
5
18
73
10

You can sort it numerically with this command:

sort -n numbers.txt

Output:

5
10
18
42
73

Sorting by Specific Field

You can sort lines based on a specific field (column) within each line using the -k option. Fields are separated by a delimiter (default is whitespace).

Example 5: Sorting by Second Field (Using Space as Delimiter)

Let's consider a file named samplefile.txt with the following content:

Banana sweet 10
Cherry sour 34
Apple yummy 5
Grapes lovely 40

To sort it by the second field, you can use this command:

sort -k2 samplefile.txt

Grapes lovely 40
Cherry sour 34
Banana sweet 10
Apple yummy 5

Consider if you want to sort by the third column containing numbers then you should use -n (numerical order) option along with -k option.

sort -n -k3 samplefile.txt

Output:

Apple yummy 5
Banana sweet 10
Cherry sour 34
Grapes lovely 40

Whereas to sort in descending order (based on the second field): sort -n -k3 -r samplefile.txt.

Example 6: Sorting by Third Field (Using a Different Delimiter)

To sort by the field using a different delimiter, you can use the -t option to specify the delimiter. Let's sort this file by the third field (city) using the colon : as the delimiter.

Contents of data.txt:

Alice:28:New York
Bob:22:Los Angeles
Charlie:35:Chicago
David:30:San Francisco

Let's sort this file by the third field (city) using the colon : as the delimiter:

sort -t':' -k3 data.txt

Output:

Charlie:35:Chicago
Bob:22:Los Angeles
Alice:28:New York
David:30:San Francisco

Example 7: Sorting column containing month

Let's take another example to sort column or field by Month

Contents of monthdata.txt:

Emily February
John January
Bob March
Alice May
Alan March

sort -k2M -k1,1 monthdata.txt

• -k2M sorts the lines based on the second column (-k2) as month names (M), considering the custom order of months.
• -k1,1 is used to specify that the first column should be used as a secondary sort key if the months are the same.

Output:

John January
Emily February
Alan March
Bob March
Alice May

Ignoring Leading Characters

The -b option allows you to ignore leading whitespace characters when sorting.

Example 8: Ignoring Leading Whitespace

The following file spacedata.txt has this content:

  Banana sweet
Cherry sour
  Apple yummy
Grapes lovely

Command:

sort -b spacedata.txt

Output:

  Apple yummy
  Banana sweet
Cherry sour
Grapes lovely

The lines are sorted alphabetically, and leading whitespace characters are ignored, which is why "Apple" and "Banana" appear first in the sorted list.

What if you need to delete leading white space and then sort lines? Use something like this:

sed 's/^ *//' spacedata.txt | sort

Case-Insensitive Sorting

To perform a case-insensitive sort on this file, you can use the -f option.

Example 9: Case-Insensitive Sorting

Content of case_sensitive.txt:

shell
kernel
terminal
GNU
Debian
Linux

Command:

sort -f case_sensitive.txt

Output:

Debian
GNU
kernel
Linux
shell
terminal

From the output, you can see the lines are sorted alphabetically while ignoring the case of the letters.

Handling Duplicate Lines

To sort the file and remove duplicate lines, you can use the -u option.

Example 10: Removing Duplicate Lines

Contents of duplicates.txt:

shell
shell
kernel
terminal
Kernel
GNU
gnu
Debian
Linux

Command

sort -u duplicates.txt

Output:

Debian
gnu
GNU
kernel
Kernel
Linux
shell
terminal

In this example, "shell" appeared twice in the original file, but they are displayed only once in the sorted and de-duplicated output. To ignore the case you can try using sort -f -u duplicates.txt.

Saving Sorted Output to a File

The -o option allows you to specify an output file directly.

Example 11: Saving Sorted Output to a File

sort -u duplicates.txt -o removed.txt

The above command removes any duplicate lines, and saves the sorted, unique lines into the removed.txt file.

The following command provides the same desired output, here we use > instead of -o:

sort -u duplicates.txt > removed.txt