The shuf command in Linux writes a random permutation of the input lines to standard output. It pseudo randomizes an input in the same way as the cards are shuffled. It is a part of GNU Coreutils and is not a part of POSIX. This command reads either from a file or standard input in bash and randomizes those input lines and displays the output.
# file shuf
shuf [OPTION] [FILE]
# list shuf
shuf -e [OPTION]... [ARG]
# range shuf
shuf -i LO-HI [OPTION]
Like other Linux commands, shuf command comes with -–help option:
[user@home ~]$ shuf --help
Usage: shuf [OPTION]... [FILE]
or: shuf -e [OPTION]... [ARG]...
or: shuf -i LO-HI [OPTION]...
Write a random permutation of the input lines to standard output.
With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too.
-e, --echo treat each ARG as an input line
-i, --input-range=LO-HI treat each number LO through HI as an input line
-n, --head-count=COUNT output at most COUNT lines
-o, --output=FILE write result to FILE instead of standard output
--random-source=FILE get random bytes from FILE
-r, --repeat output lines can be repeated
-z, --zero-terminated line delimiter is NUL, not newline
shuf
When shuf command is used without any argument in the command line, it takes input from the user until CTRL-D is entered to terminate the set of inputs. It displays the input lines in a shuffled form. If 1, 2, 3, 4 and 5 are entered as input lines, then it generates 1, 2, 3, 4 and 5 in random order in the output as seen in the illustration below:
[user@home ~]$ shuf
1
2
3
4
5
4
5
1
2
3
Consider an example where Input is taken from the pipe:
{
seq 5 | shuf
}
seq 5 returns the integers sequentially from 1 to 5 while the shuf command takes it as input and shuffles the content i.e, the integers from 1 to 5. Hence, 1 to 5 is displayed as output in random order.
[user@home ~]$ {
> seq 5 | shuf
> }
5
4
2
3
1
When shuf command is used without -e or -i option, then it operates as a file shuf i.e, it shuffles the contents of the file. The <file_name> is the last parameter of the shuf command and if it is not given, then input has to be provided from the shell or pipe.
Consider an example where input is taken from a file:
shuf file.txt
Suppose file.txt contains 6 lines, then the shuf command displays the input lines in random order as output.
[user@home ~]$ cat file.txt
line-1
line-2
line-3
line-4
line-5
[user@home ~]$ shuf file.txt
line-5
line-4
line-1
line-3
line-2
Any number of lines can be randomized by using -n option.
shuf -n 2 file.txt
This will display any two random lines from the file.
line-5
line-2
When -e option is used with shuf command, it works as a list shuf. The arguments of the command are taken as the input line for the shuf.
Consider an example:
shuf -e A B C D E
It will take A, B, C, D, E as input lines, and will shuffle them to display the output.
A
C
B
D
E
Any number of input lines can be displayed using the -n option along with -e option.
shuf -e -n 2 A B C D E
This will display any two of the inputs.
E
A
When -i option is used along with shuf command, it acts as a range shuf. It requires a range of input as input where L0 is the lower bound while HI is the upper bound. It displays integers from L0-HI in shuffled form.
[user@home ~]$ shuf -i 1-5
4
1
3
2
5
The shuf command helps you randomize input lines. And there are features to limit the number of output lines, repeat lines and even generate random positive integers. Once you're done practicing whatever we've discussed here, head to the tool's man page to know more about it.