PowerShell 避免使用脚本范围的变量

Question

我写了一个函数来检查主机是在线还是离线并返回$true或$false。此功能完美运行，我想通过查看来改进它 是否可以删除脚本范围的变量，例如 $Script:arrayCanPingResult 和 $script:tmpPingCheckServers。

我为什么要这个？ 当我在foreach 循环中调用该函数时，我通常使用开关-Remember，因此它不会检查同一主机两次。为了能够正确使用它，我必须通过将两个变量都声明为空（$Script:arrayCanPingResult=$script:tmpPingCheckServers=@{}）来开始我使用此函数的所有脚本。而且我可以想象人们忘记将第一行放在他们的脚本中，并且在 PowerShell ISE 编辑器中进行多次测试时，当主机已经在 ISE 中检查过一次（F5）时，它不会在第二次运行时再次进行测试.

在这种情况下，有没有办法避免使用脚本范围的变量？所以我们不需要在新脚本的开头声明它们为空？如果这是可能的，那就太好了，因为我们可以在自定义模块中包含这个函数。

一如既往，感谢您的建议或帮助。在你们这里​​我真的学到了很多东西。

# Function to check if $Server is online
Function Can-Ping ($Server,[switch]$Remember) {

    $PingResult = {
          # Return $true or $false based on the result from script block $PingCheck
          foreach ($_ in $Script:arrayCanPingResult) { 
                   # Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: $_ " -ForegroundColor Green
                   if ($Server -eq $($_.Split(",")[0])) {

                   #Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: We will return $($_.Split(",")[1])" -ForegroundColor Green
                    return $($_.Split(",")[1])  
                   } 
          }
    }

    $PingCheck = {

        $Error.Clear()

        if (Test-Connection -ComputerName $Server -BufferSize 16 -Count 1 -ErrorAction 0 -quiet) { # ErrorAction 0 doesn't display error information when a ping is unsuccessful

            Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Ping test ok" -ForegroundColor Gray; $Script:arrayCanPingResult+=@("$Server,$true"); return
        } 
        else {
            $Error.Clear()
            Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Ping test FAILED" -ForegroundColor Gray

            Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Flushing DNS" -ForegroundColor Gray
            ipconfig /flushdns | Out-Null

            Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Registering DNS" -ForegroundColor Gray
            ipconfig /registerdns | Out-Null

            Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: NSLookup" -ForegroundColor Gray
            nslookup $Server | Out-Null # Suppressing error here is not possible unless using '2> $null', but if we do this, we don't get $true or $false for the function so '| Out-Null' is an obligation
            if (!$?) {
                Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: NSlookup can't find the host '$Server', DNS issues or hostname incorrect?" -ForegroundColor Yellow
                # Write-Host $Error -ForegroundColor Red
                if ($SendMail) {
                    Send-Mail $MailTo "FAILED Ping test" "$(Get-TimeStamp) NSlookup can't find the host '$Server', hostname incorrect or DNS issues?" "<font color=`"red`">$error</font>"
                }
                $script:arrayCanPingError += "ERROR | $(Get-TimeStamp) Ping test failed: NSlookup can't find the host '$Server', hostname incorrect or DNS issues?$error"
                $script:HTMLarrayCanPingError += "ERROR | $(Get-TimeStamp) Ping test failed:<br>NSlookup can't find the host '$Server', hostname incorrect or DNS issues?<br><font color=`"red`">$error</font>"
                $Script:arrayCanPingResult+=@("$Server,$false")
                return
                }
            else {
                Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Re-pinging '$Server'" -ForegroundColor Gray
                if (Test-Connection -ComputerName $Server -BufferSize 16 -Count 1 -ErrorAction 0 -Quiet) {
                   Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Ping test ok, problem resolved" -ForegroundColor Gray
                   $Script:arrayCanPingResult+=@("$Server,$true")
                   return
                }
                else {
                      Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: DNS Resolving is ok but can't connect, server offline?" -ForegroundColor Yellow
                      if ($SendMail) {
                          Send-Mail $MailTo "FAILED Ping test" "$error" "DNS Resolving is ok but can't connect to $Server, server offline?"
                      } 
                      $script:arrayCanPingError += "ERROR Ping test failed: DNS Resolving is ok but can't connect to $Server, server offline?$error"
                      $script:HTMLarrayCanPingError += "ERROR Ping test failed: DNS Resolving is ok but can't connect to $Server, server offline?<br><font color=`"red`">$error</font>"
                      $Script:arrayCanPingResult+=@("$Server,$false")
                      return
                }
            }
        }
    }

    # Call the script block $PingAction every time, unless the switch $Remember is provided, than we only check each server once
    if ($Remember) {
        Write-Host "$(Get-TimeStamp) $Server > Function Can-Ping: Switch '-Remember' detected" -ForegroundColor Gray
        While ($tmpPingCheckServers -notcontains $Server) { 
                  &$PingCheck
                  $script:tmpPingCheckServers = @($tmpPingCheckServers+$Server) #Script wide variable, otherwise it stays empty when we leave the function / @ is used to store it as an Array (table) instead of a string
        }
        &$PingResult
    } 
    else {
          &$PingCheck
          &$PingResult
    }
}

Answer 1

我会这样做：

function Get-PingStatus {
    param(
        # Server object.
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        $Server,
        [Parameter(Mandatory=$false)]
        [Bool]$UseLastPingResult = $false
    )

    if ( ($UseLastPingResult) `
    -and (! [String]::IsNullOrEmpty($Server.LastPingResult)) ) {
        # Return unmodified object if LastPingResult property is not empty.
        return $Server 
    }

    try {
        $oPingResult = Test-Connection -ComputerName $Server.Name `
        -BufferSize 16 -Count 1 -ErrorAction Stop

        $Server.LastPingResult = "success"
        # And just in case.
        $Server.IPV4Address = $oPingResult.IPV4Address
    }
    catch {
        $Server.LastPingResult = "failure"
    }

    return $Server
}

对象输入，对象输出。一般来说，这是编写 PowerShell 函数的最佳方法，因为：1) 它与常用 cmdlet 的功能一致；2) 它可以帮助您保持代码的简单和可读性。

使用 ErrorAction -Stop 和 try...catch...finally 也比 ErrorAction -SilentlyContinue 之后检查一些变量更好。

现在让我们假设 $cServerNames 是服务器名称或任何可以解析为 IP 地址的集合。示例：@("server1", "server2", "1.2.3.4", "webserver.example.com")。

# Converting strings to objects.
$cServers = @()
foreach ($sServerName in $cServerNames) {
    $oServer = New-Object PSObject -Property @{
        "Name" = $sServerName;
        "IPV4Address" = $null;
        "LastPingResult" = $null;
    }

    $cServers += $oServer
}

# Now we can iterate objects and update their properties as necessary.
foreach ($oServer in $cServers) {
    $oServer = Get-PingStatus -Server $oServer -UseLastPingResult

    if ($oServer.LastPingResult -eq "success") {
        # Do something.
    } else {
        # Do something else like an error message.
    }
}

您可以添加任何您想要的诊断输出，但我建议您使用 Write-Output 和/或 Write-Error 而不是 Write-Host。

最后，请注意，在大多数情况下，ping 在生产代码中几乎没有用处。这是多余的，无论主机是否回复，都无法证明。例如，ping 可能没问题，但由于某种原因，您在后续的 Get-WmiObject 查询中遇到异常。如果出于性能原因（以节省时间）执行 ping，则应考虑通过 background jobs 或 workflows 并行运行脚本块。