Powershell：日期时间星期几比较逻辑 [英] Powershell: Date Time day of the week comparison logic

问题描述

Date Time对象允许我们执行如下操作：

  $ CurrentDate = Get-Date 
 $ TextDate = get-date -date02/10/2016
 
 if（$ TextDate -lt $ CurrentDate）{Write-HostTrue} 
 else {Write-HostFalse 
  

输出True，因为$ TextDate小于$ CurrentDate。

遵循相同的逻辑，为什么以下代码输出错误？

  $ CurrentDate = Get-Date -UFormat％V 
 $ TextDate = Get-Date -date02/10/2016
 $ TextDate = Get-Date -date $ TextDate -UFormat％V 
 
 if（$ TextDate -lt $ CurrentDate）{Write-HostTrue} 
 else {Write-HostFalse} 
  pre> 
 
 
唯一的区别是我们正在比较一年中的一周。如果将比较改为-gt，代码将返回True。
解决方案
格式化的日期是字符串，而不是整数。字符串6在字符串11之后。
 
 
 
这将是最正确的方法：
 
 
 
首先，决定一年的第一个星期实际意味着什么：
  $ CalendarWeekRule = [System.Globalization.CalendarWeekRule] :: FirstDay; 
＃$ CalendarWeekRule = [System.Globalization.CalendarWeekRule] :: FirstFourDayWeek; 
＃$ CalendarWeekRule = [System.Globalization.CalendarWeekRule] :: FirstFullWeek; 
  
然后，决定一周的哪一天是一周的第一天：
  $ FirstDayOfWeek = [System.DayOfWeek] ::星期日; 
＃$ FirstDayOfWeek = [System.DayOfWeek] ::星期一
＃有一天可用
  
然后你可以得到正确的周号码：
  $ Today =（Get-Date）.Date; 
 $ TodayWeek = [cultureinfo] :: InvariantCulture.Calendar.GetWeekOfYear（$ Today，$ CalendarWeekRule，$ FirstDayOfWeek）; 
 
 $ TargetDate = Get-Date -Date2016-02-10; 
 $ TargetWeek = [cultureinfo] :: InvariantCulture.Calendar.GetWeekOfYear（$ TargetDate，$ CalendarWeekRule，$ FirstDayOfWeek）; 
 
 if（$ TargetWeek -lt $ TodayWeek）{$ true} else {$ false} 
  
请注意，如果您想要一个完整的ISO 8601周，它是稍微复杂一些。
 
Date Time objects allow us to perform actions like this:
$CurrentDate = Get-Date
$TextDate = get-date -date "02/10/2016"

if ($TextDate -lt $CurrentDate){ Write-Host "True" }
else{ Write-Host "False" }
This outputs "True" because $TextDate is less than $CurrentDate.  

Following the same logic, why does the following code output false?
$CurrentDate = Get-Date -UFormat %V
$TextDate = Get-Date -date "02/10/2016" 
$TextDate = Get-Date -date $TextDate -UFormat %V  

if ($TextDate -lt $CurrentDate){ Write-Host "True" }
else{ Write-Host "False" }
The only difference is that we are comparing the week of the year.  If you change the comparison to -gt, the code returns True.
解决方案
Formatted dates are strings, not integers.  The string "6" is after the string "11".

This would be the most correct way to do this:

First, decide what the "first week of the year" actually means:
$CalendarWeekRule = [System.Globalization.CalendarWeekRule]::FirstDay;
#$CalendarWeekRule = [System.Globalization.CalendarWeekRule]::FirstFourDayWeek;
#$CalendarWeekRule = [System.Globalization.CalendarWeekRule]::FirstFullWeek;
Then, decide which day of the week is the first day of the week:
$FirstDayOfWeek = [System.DayOfWeek]::Sunday;
#$FirstDayOfWeek = [System.DayOfWeek]::Monday;
#Any day is available
Then you can get your correct week number:
$Today = (Get-Date).Date;
$TodayWeek = [cultureinfo]::InvariantCulture.Calendar.GetWeekOfYear($Today, $CalendarWeekRule, $FirstDayOfWeek);

$TargetDate = Get-Date -Date "2016-02-10";
$TargetWeek = [cultureinfo]::InvariantCulture.Calendar.GetWeekOfYear($TargetDate, $CalendarWeekRule, $FirstDayOfWeek);

if ($TargetWeek -lt $TodayWeek) { $true } else { $false }
Note that if you want a full ISO 8601 week, it's somewhat more complicated.

                        
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