while :; do clear; your_command; sleep 2; done


基于此你可以实现一个watch.sh脚本来实现watch

#!/bin/bash
# usage: watch.sh <your_command> <sleep_duration>

while :; 
  do 
  clear
  date
  $1
  sleep $2
done


参考资料：

https://stackoverflow.com/questions/9574089/os-x-bash-watch-command