为什么-Verbose会禁用$ErrorActionPreference？

Question

让我们以这个脚本为例：

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

try
{
  echo "ErrorActionPreference = $ErrorActionPreference"
  Copy-Item  "this_is_a_bad_path" 
  Write-Host "Did not catch error"
}
catch
{
    Write-Host "Caught Error"
}

这与以下输出的预期效果相同：

ErrorActionPreference = Stop
Caught Error

但是，如果我将-verbose添加到行中，并给出Copy-Item -verbose "this_is_a_bad_path"，则不再使用$ErrorActionPrefrence，并得到以下输出：

ErrorActionPreference = Stop
Copy-Item : Cannot find path 'C:\Users\porter.bassett\this_is_a_bad_path' because it does not exist.
At C:\Users\porter.bassett\dot.ps1:7 char:3
+   Copy-Item -verbose "this_is_a_bad_path"
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:\Users\porter...s_is_a_bad_path:String) [Copy-Item], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.CopyItemCommand

Did not catch error 

为了让它在-verbose打开、打开的情况下正常工作，我必须将-ErrorAction Stop添加到给出Copy-Item -verbose "this_is_a_bad_path" -ErrorAction Stop的代码行中

为什么在使用-Verbose时不能依赖$ErrorActionPreference

Answer 1

这也是Technet上讨论的PowerShell中的一个特性/错误：Verbose common parameter disables ErrorActionPreference。

这个特性/错误在PowerShell 4和最新版本5中也存在。

Answer 2

好吧，我不知道为什么，但是这个triple face palm问题(好吧，至少是IMHO)，在开放源码的PS代码中仍然有效：

https://github.com/PowerShell/PowerShell/blob/02b5f357a20e6dee9f8e60e3adb9025be3c94490/src/System.Management.Automation/engine/MshCommandRuntime.cs#L3207：

    /// <summary>
    /// ErrorAction tells the command what to do when an error occurs
    /// </summary>
    /// <exception cref="System.Management.Automation.ExtendedTypeSystemException">
    /// (get-only) An error occurred accessing $ErrorAction.
    /// </exception>
    /// <remarks>
    /// This is a common parameter via class CommonParameters.
    /// </remarks>
    internal ActionPreference ErrorAction
    {
        get
        {
            // Setting CommonParameters.ErrorAction has highest priority
            if (IsErrorActionSet)
                return _errorAction;

            // Debug takes preference over Verbose
            if (Debug)
                return ActionPreference.Inquire;
            if (Verbose)
                return ActionPreference.Continue; *** WTF!?! ***

            // fall back to $ErrorAction
            if (!_isErrorActionPreferenceCached)
            {
                bool defaultUsed = false;
                _errorAction = Context.GetEnumPreference<ActionPreference>(SpecialVariables.ErrorActionPreferenceVarPath, _errorAction, out defaultUsed);
                _isErrorActionPreferenceCached = true;
            }
            return _errorAction;
        }

Answer 3

最好的办法是为模块中的每个命令指定erroraction。

write-host foo -ErrorAction Stop

更新:这篇博文很有帮助。它解释了全局var继承如何导致观察到的行为。

https://blogs.technet.microsoft.com/heyscriptingguy/2014/04/26/weekend-scripter-access-powershell-preference-variables/