execute a command repeatedly

poll

#!/bin/sh -e
delimiter='\
'
interval=1
while getopts d:i: opt; do
	case $opt in
	d)	delimiter=$OPTARG;;
	i)	interval=$OPTARG;;
	\?)	exit 1;;
	esac
done
shift $((OPTIND-1))
while sleep -- "$interval"; do
	"$@" | sed ":a;\$!{N;s/\n/$delimiter/;ba;}"
done

poll.1.txt

NAME
	poll - execute a command repeatedly

SYNOPSIS
	poll [-i interval] [-d delimiter] [command ...]

DESCRIPTION
	The poll utility executes command at one-second intervals until
	it fails.
	
	The options are as follows:
	
	-i interval
		Set the execution interval (in seconds).
	
	-d delimiter
		Replace all newlines (except the last) in the output
		of command with the delimiter string.  Any forward
		slashes and newlines in the string must be escaped with
		backslashes.