Bash implementation of `watch`

watch.sh

#!/usr/bin/env bash
#
# Usage: watch.sh "<command>" [interval]
# https://stackoverflow.com/questions/9574089/os-x-bash-watch-command

pid=$$

command="$1"
# default interval of 2 seconds
interval="${2:-2}"

reserved_line_count=3
lines=$(($(tput lines) - $reserved_line_count))
header_mode='clear
setaf 0
setab 7
'
buffer="$(mktemp watch-sh-XXXXXX)"

function onexit() {
	tput rmcup
	rm -f "$buffer"
}

trap onexit EXIT

tput smcup

KEY=" "

while [[ "$KEY" != "q" ]]; do {
	printf "%s\t%s (PID=%s)%s\n\n" "$(tput -S <<< "$header_mode")" "$(date)" "$pid" "$(tput sgr0)"
	bash -c "$command" | tee "$buffer" | head -n $lines
	read -s -t $interval -n 1 KEY
} done