How to Randomize Lines of Text Using the shuf Command in Linux

When working with massive text datasets in a Linux terminal, you will often need to randomize the order of the data. You might need to shuffle a list of survey participants, randomize the lines in a CSV file to train a machine learning model, or simply pick a random winner from a list of names. While writing a Python script to do this is common, Linux includes a native utility called shuf (shuffle) that can generate perfectly random permutations of lines directly from the command line.

How to Shuffle a Text File

The shuf command is incredibly simple to use. At its most basic, you just pass it the name of a file. It will read the entire file into memory, randomize the order of every single line, and print the resulting chaos to the standard output (your terminal screen).

Imagine you have a file named contestants.txt containing five names:

Alice
Bob
Charlie
David
Eve

If you run the command:

shuf contestants.txt

The output will be completely randomized, for example:

David
Alice
Eve
Bob
Charlie

Because the output goes directly to the terminal, the original contestants.txt file remains completely untouched and perfectly ordered.

How to Select a Random Subset (The “Winner”)

One of the most powerful features of shuf is its ability to not just shuffle a list, but also truncate the output. By using the -n (head count) flag, you can tell the utility to shuffle the entire file but only output the top N results.

If you have a file containing 10,000 email addresses and you want to pick exactly three random winners for a giveaway, you would run:

shuf -n 3 emails.txt

The utility performs a true random shuffle of all 10,000 lines, but stops and prints only the first three results, providing a perfectly randomized subset.

Generating Random Numbers

The shuf command is not limited to reading text files. You can also use it as a powerful random number generator by utilizing the -i (input range) flag. You must provide a low number and a high number separated by a hyphen.

To simulate a six-sided die roll, you want a single random number between 1 and 6. You would combine the input range flag with the head count flag:

shuf -i 1-6 -n 1

The terminal will instantly output a single random integer (e.g., 4).

If you wanted to simulate a lottery draw by picking five unique, non-repeating numbers between 1 and 50, you would run:

shuf -i 1-50 -n 5

The output will display five completely random, distinct numbers, making shuf one of the most versatile scripting tools available in bash.