使用 PROMPT COMMAND envrionment 變數

當完成互動式 bash 例項中的最後一個命令時，將顯示已評估的 PS1 變數。在實際顯示 PS1 之前，bash 會檢視是否設定了 PROMPT_COMMAND。此 var 的值必須是可呼叫的程式或指令碼。如果設定了此 var，則在顯示 PS1 提示之前呼叫此程式/指令碼。

# just a stupid function, we will use to demonstrate
# we check the date if Hour is 12 and Minute is lower than 59
lunchbreak(){ 
   if (( $(date +%H) == 12 && $(date +%M) < 59 )); then 
      # and print colored \033[ starts the escape sequence 
      # 5; is blinking attribute
      # 2; means bold
      # 31 says red
      printf "\033[5;1;31mmind the lunch break\033[0m\n";
   else
      printf "\033[33mstill working...\033[0m\n"; 
   fi; 
}

# activating it
export PROMPT_COMMAND=lunchbreak