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CJ--
Asked: 2020-07-09 12:53:37 +0800 CST

在bash中减去日期格式

  • 772

我正在尝试创建倒计时 - 很可能是艰难的方式。我有这样的设置：

#! /bin/bash 

#When to execute command 
execute=$(date +"%T" -d "22:30:00")

#Current time
time=$(date +"%T")

#Subtract one from the other.... the below is line 11
math=$(("$execute"-"$time"))

#Repeat until time is 22:30:00
until [ "$math" == "00:00:00" ]; do  

echo "Countdown is stopping in $math"
sleep 1
clear 
done

问题是......它不起作用。这是终端中的输出：

   /path/to/file/test.sh: line 11: 22:30:00-16:39:22: syntax error in expression (error token is “:30:00-16:39:22”) 
    Countdown is stopping in

首先，错误信息，有什么问题？

其次，“倒计时正在停止”消息应该有倒计时将停止的小时、分钟和秒。为什么不呢？请记住，我不是专业人士。

scripts bash time date syntax

2 个回答

  1. Best Answer

    问题在于声明

    math=$(("$execute"-"$time"))

    因为executeandtime包含格式中的值%H:%M:%S。但是 bash 的算术扩展不能评估时间格式。

    除了%H:%M:%S格式，您可以将时间转换为秒，进行算术运算，然后以所需的格式打印。

    就像是

    #!/bin/bash

#When to execute command
execute=$(date +"%s" -d "22:30:00")

time=$(date +"%s")
math=$((execute-time))

if [[ $math -le 0 ]]; then
    echo "Target time is past already."
    exit 0
fi

#Repeat until time is 22:30:00
while [[ $math -gt 0 ]]; do
    printf "Countdown is stopping in %02d:%02d:%02d" $((math/3600)) $(((math/60)%60)) $((math%60))
    sleep 1
    clear

    # Reset count down using current time;
    # An alternative is to decrease 'math' value but that
    # may be less precise as it doesn't take the loop execution time into account
    time=$(date +"%s")
    math=$((execute-time))
done
    • 1

  2. 谢谢@PP 的回答。您的方法起初有效，但在重新启动后停止工作....此外，它并没有停止循环 - 这意味着它进入负数并且之后从未执行过命令。这就是我最终做的事情：

    #! /bin/bash

#When to execute command
execute=$(date +"%s" -d "22:30:00")

time=$(date +"%s")
math=$((execute-time))

#Repeat until time is 22:30:00
until [ "$time" == "$execute" ]; do
    printf "The server will stop in %02d:%02d:%02d" $((math/3600)) $(((math/60)%60)) $((math%60))
    sleep 1
    clear

    # Reset count down using current time;
    # An alternative is to decrease 'math' value but that
    # may be less precise as it doesn't take the loop execution into account
    time=$(date +"%s")
    math=$((execute-time))

if [ "$time" == "$execute" ]; then

break
fi 

done 

echo "Cycle has ended"
    • 1

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