rl - Randomize Lines.

rl [OPTION]... [FILE]...

rl reads lines from a input file or stdin, randomizes the lines and outputs a specified number of lines. It does this with only a single pass over the input while trying to use as little memory as possible.

-c, --count=N

Select the number of lines to be returned in the output. If this argument is omited all the lines in the file will be returned in random order. If the input contains less lines than specified and the --reselect option below is not specified a warning is printed and all lines are returned in random order.

-r, --reselect

When using this option a single line may be selected multiple times. The default behaviour is that any input line will only be selected once. This option makes it possible to specify a --count option with more lines than the file actually holds.

-o, --output=FILE

Send randomized lines to FILE instead of stdout.

-d, --delimiter=DELIM

Use specified character as a "line" delimiter instead of the newline character.

-0, --null

Input lines are terminated by a null character. This option is useful to process the output of the GNU find -print0 option.

-q, --quiet, --silent

Be quiet about any errors or warnings.

-h, --help

Show short summary of options.

-v, --version

Show version of program.

Some simple demonstrations of how rl can help you do everyday tasks. Warning: some of these examples may affect the operation of your system.

Play a random sound after 4 minutes (perfect for toast): sleep 240 ; play `find /sounds -name '*.au' -print | rl --count=1`

Renice all the processes of a random logged-in user: renice +5 -u `who | cut '-d ' -f 1 | sort -u | rl --count=1`

Kill a random process on your computer. kill -9 `ps -A | awk '{print $1}' | rl --count=1`

Do this as root and see how long your system keeps working. Increase the --count for extra effect. (you may need to change the ps and awk parameters depending on your system)

Find all movies and play them in random order. find . -name '*.avi' -print0 | rl -0 | xargs -n 1 -0 mplayer

Because -0 is used filenames with spaces (even newlines and other unusual characters) in them work.

The program currently does not have very smart memory management. If you feed it huge files and expect it to fully randomize all lines it will completely read the file in memory. If you specify the --count option it will only use the memory required for storing the specified number of lines. Improvements on this area are on the TODO list.

The program uses the rand() system random function. This function returns a number between 0 and RAND_MAX, which may not be very large on some systems. This wil result in non-random results for files containing more lines than RAND_MAX.

Note that if you specify multiple input files they are randomized per file. This is a different result from when you cat all the files and pipe the result into rl.

Copyright © 2001, 2002, 2003, 2004, 2005 Arthur de Jong <arthur@tiefighter.et.tudelft.nl>.

This is free software; see the license for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.