Intro To 'shuf' Command In Linux

2023-06-06 - By Robert Elder

     I use the 'shuf' command to generate random permutations of lines in a file:

shuf my-file.txt

Randomize Lines In A File

     Here, I have a file called 'students.txt' that contains a sorted list of students in a class:

Charles
Christopher
David
Elizabeth
Jennifer
Jessica
Karen
Linda
Lisa
Mary
Michael
Patricia
Richard
Susan
William

     I want to randomly rearrange the lines in this file to provide a seating assignment for each student.  I can use the 'shuf' command to generate a new randomly rearranged list like this:

cat students.txt | shuf

Michael
Karen
David
Susan
Patricia
Mary
Lisa
Elizabeth
Richard
Linda
Jennifer
Charles
Christopher
Jessica
William

Select N Random Lines From A File Without Replacement

     If I want to randomly select only three of the students from this list I can use the '-n' flag like this:

cat students.txt | shuf -n 3

Jennifer
Jessica
Karen

Select N Random Lines From A File With Replacement

     By default, the 'shuf' command prints out each line only once.  If you use the '-r' flag, all of the lines will be repeated an infinite number of times randomly so that duplicate lines can occur:

cat students.txt | shuf -r

Jessica
Michael
Michael
William
Richard
... Lines printed until you use Ctrl + C...

     Using the 'head' command I can limit the output to the first 10 lines:

cat students.txt | shuf -r | head -n 10

Susan
Richard
Richard
Michael
Michael
Patricia
Karen
Michael
Jessica
Elizabeth

     Notice how the output now contains duplicate lines (in this case, 'Richard' and 'Michael').

     For another example use of the '-r' flag, I can create 15 random samples from the file 'key-strokes.txt':

KEY_UP
KEY_DOWN
KEY_LEFT
KEY_RIGHT

     using the following command:

cat key-strokes.txt | shuf -r | head -n 15

KEY_LEFT
KEY_LEFT
KEY_DOWN
KEY_RIGHT
KEY_UP
KEY_DOWN
KEY_UP
KEY_RIGHT
KEY_LEFT
KEY_LEFT
KEY_UP
KEY_DOWN
KEY_UP
KEY_LEFT
KEY_DOWN

Generate Random Numbers Filling A Range

     I can also use the '-i' flag to specify a number range and the output will produce random numbers filling this range:

shuf -i 1-10

9
3
5
6
10
1
7
2
8
4

shuf -i 92-106

96
105
98
93
94
104
103
106
92
102
95
101
100
97
99

     And that's why the 'shuf' command is my favourite Linux command.