每當您嘗試使用尚未初始化的變數時,值會是 $null。 這是$null值潛入程式代碼的最常見方式之一。PowerShell 複製 PS> $null -eq $undefinedVariable True 如果您碰巧誤寫變數名稱,則 PowerShell 會將它視為不同的變數,且值為 $null。您找到$null值的另一種方式是從不提供任何結果的其他命令中獲得這些值。
查看所有定义的变量的命令“ls variable:”,查询以a开头的变量如下: PSC:\Powershell>$a1,$a2,$a3=10,20,30PSC:\Powershell>lsvariable:a* Name Value---a20a110a330a220args {}PSC:\Powershell>$a=$NULLPSC:\Powershell>lsvariable:a* Name Value---a a110a330a220args {} ④环境变量 $env:中的环...
若要从变量中删除所有值,可以将该变量设置为等于$null。$null变量由 Windows PowerShell 自动定义为无。 例如: PowerShell $num1=$null$str1=$null 备注 若要清除变量,还可以使用 Clear-Variable。 可以将数学运算符与变量一起使用,如以下示例所示:
-ErrorAction:SilentlyContinue parameter is not being respected & $error variable not updated -ExpandProperty & Export CSV !!! powershell script to add a word in the beginning of the text file - URGENT !!! 'A positional parameter cannot be found that accepts argument '$null'. 'Name' Attribut...
Example 3: Delete the value of the specified variable PowerShell Clear-Variable-Name"Processes" This command deletes the value of the variable named Processes. After the cmdlet completes the operation, the variable named Processes still exists, but the value is null. ...
Often in your scripts, you may need to check if a variable is $null or if a property is $null before using it. The new Null conditional operators makes this simpler. The new??null coalescing operator removes the need forifandelsestatements if you want to get the value of a statement ...
当第一个命令是 CDXML 函数,下游包含 CimCmdlet cmdlet 或 CDXML 函数时,PipelineVariable将重置为$null。 PowerShell Get-Partition-pvpvar |ForEach-Object{Write-Host"Before: $($pvar.PartitionNumber)"[pscustomobject]@{Filter="Index = $($_.DiskNumber)"} } |Get-CimInstanceWin32_DiskDrive |ForEach-...
此命令将获取本地计算机上的所有事件日志。 日志按Get-WinEvent获取日志的顺序列出。 首先检索经典日志,然后检索新的 Windows 事件日志。 日志的RecordCount可以为 null(为空或零)。 PowerShell Get-WinEvent-ListLog* LogMode MaximumSizeInBytes RecordCount LogName --- --- --- --- Circular1553203214500Applicat...
A null-conditional operator applies a member access,?., or element access,?[], operation to its operand only if that operand evaluates to non-null; otherwise, it returns null. Since PowerShell allows?to be part of the variable name, formal specification of the variable name is required for...
3/15/2019 13:54:13 600 Information Provider "Variable" is Started... 3/15/2019 13:54:13 600 Information Provider "Function" is Started... 3/15/2019 13:54:13 600 Information Provider "FileSystem" is Started... Get-WinEvent cmdlet 从计算机获取日志信息。 Path 参数指定目录和文件名。