repeat a command in bash

repeat.sh

#!/usr/bin/env bash

# repeat.sh
#
# Usage:
#   repeat <command>
# will repeat <command> forever.
#
#   repeat -nN <command>
# will repeat <command> N times.
#
#   repeat -iT <command>
# will repeat <command> every T seconds.

fail() {
  echo "$1" >&2
  exit 1
}

declare -i times interval
times=-1
interval=0

while getopts 'n:i:' option; do
  case $option in
    n) 
      let "times = $OPTARG"
    ;;

    i) 
      let "interval = $OPTARG"
    ;;
  esac
done

shift $((OPTIND - 1))

if [[ $# == 0 ]]; then
  fail "Usage: $0 [-n-i] COMMAND"
fi

test $times -gt 0
infinite_loop=$?

command=$*

while (( $times > 0 || $infinite_loop )); do
  eval "$command" &
  ((times--))

  if (( $times > 0 || $infinite_loop )); then
    sleep $interval
  fi
done

wait