shuf - Linux

Overview

The shuf command in Linux is used for generating random permutations of input lines. It can shuffle lines from a specified file or standard input and outputs them. This is useful in various scenarios like random sampling, creating test cases, or simply randomizing the order of lines in a file.

Syntax

The basic syntax for the shuf command is:

shuf [OPTION]... [FILE]
  • [FILE]: The name of the file whose lines will be shuffled. If no file is specified, or if the filename provided is -, shuf reads from standard input.

Variations

shuf -e [OPTION]... [ARG]...
shuf -i LO-HI [OPTION]...
  • -e: Treat each command-line argument as an input line.
  • -i: Generate output consisting of random numbers from range LO to HI inclusive.

Options/Flags

  • -n, –head-count=COUNT: Output at most COUNT lines. By default, all input lines are output.
  • -o, –output=FILE: Write result to FILE instead of standard output.
  • -r, –repeat: Repeat output values, i.e., allow lines to be repeated in the output.
  • -z, –zero-terminated: Line delimiter is NUL, not newline.

Examples

1. Shuffle lines of a file and display on standard output:

shuf myfile.txt

2. Generate 5 random numbers from 1 to 100:

shuf -i 1-100 -n 5

3. Shuffle lines of a file and save them to another file:

shuf -o shuffled.txt myfile.txt

4. Shuffle and repeat lines:

shuf -r -n 20 myfile.txt

Common Issues

  • File Not Found: Ensure the file path is correct. The command will error if the specified file does not exist.
  • Permission Denied: shuf requires read permissions on the files it processes. Ensure appropriate permissions are set.

Integration

shuf can be integrated with other commands via pipes to perform complex tasks:

cat myfile.txt | shuf | grep 'pattern'

This command chain will shuffle the lines of myfile.txt, then pass the shuffled content through grep to filter lines matching a pattern.

Another integration could be with loops for scripting:

for i in {1..10}; do shuf -n 1 file.txt; done

This loop shuffles file.txt and prints one line each loop iteration, useful for drawing random samples.

  • sort: Sort lines of text files.
  • awk: Pattern scanning and processing language.
  • grep: Searches for and prints out text matching a pattern.

For more details and further examples, consult the shuf man page (man shuf) or the GNU Coreutils online documentation.