little-things/sample

#!/usr/bin/env bash
if [[ "$#" -eq 0 || ( "$#" -eq 2 && "$1" != '-0' ) || "$#" -gt 2 || "${@: -1}" != @(1?(.+(0))|0?(.+([0-9]))) ]]; then
	printf 'Usage: sample [-0] PROBABILITY\n' >&2
	printf 'Read lines from stdin, and print each line again with a given probability (a number between 0 and 1).\n' >&2
	printf 'With -0, use NUL instead of line feeds on both input and output.\n' >&2
	exit 1
fi

if [[ "$#" -eq 2 && "$1" == '-0' ]]; then
	awkopts=(-v 'RS=\000' -v 'ORS=\000')
	shift
fi

exec awk "${awkopts[@]}" -v "prob=$1" 'rand() <= prob'