Invoke-Expression

Invoke-Expression
    [-Command] <String>
    [<CommonParameters>]

The Invoke-Expression cmdlet evaluates or runs a specified string as a command and returns the results of the expression or command. Without Invoke-Expression, a string submitted at the command line would be returned (echoed) unchanged.

PS C:\> $Command = "Get-Process"
PS C:\> $Command
Get-Process
PS C:\> Invoke-Expression $Command
Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id   ProcessName
-------  ------    -----      ----- -----   ------     --   -----------
296       4       1572       1956    20       0.53     1348   AdtAgent
270       6       1328       800     34       0.06     2396   alg
67        2       620        484     20       0.22     716    ati2evxx
1060      15      12904      11840   74       11.48    892    CcmExec
1400      33      25280      37544   223      38.44    2564   communicator
...

This example demonstrates the use of Invoke-Expression to evaluate an expression. Without Invoke-Expression, the expression is printed, but not evaluated.

The first command assigns a value of Get-Process (a string) to the $Command variable.

The second command shows the effect of typing the variable name at the command line. Windows PowerShell echoes the string.

The third command uses Invoke-Expression to evaluate the string.

PS C:\> Invoke-Expression -Command "C:\ps-test\testscript.ps1"
PS C:\> "C:\ps-test\testscript.ps1" | Invoke-Expression

These commands use Invoke-Expression to run a script, TestScript.ps1, on the local computer. The two commands are equivalent. The first uses the Command parameter to specify the command to run. The second uses a pipeline operator (|) to send the command string to Invoke-Expression.

PS C:\> $Command = 'Get-Process | where {$_.cpu -gt 1000}'
PS C:\> Invoke-Expression $Command

This example runs a command string that is saved in the $Command variable.

The command string is enclosed in single quotation marks because it includes a variable, $_, which represents the current object. If it were enclosed in double quotation marks, the $_ variable would be replaced by its value before it was saved in the $Command variable.

PS C:\> $Cmdlet_name = "Get-EventLog"
PS C:\> $Example_number = 1
PS C:\> $Example_code = (Get-Help $Cmdlet_name).examples.example[($Example_number-1)].code
PS C:\> Invoke-Expression $Example_code

This command retrieves and runs the first example in the Get-EventLog cmdlet Help topic.

To run an example of a different cmdlet, change the value of the $Cmdlet_name variable to the name of the cmdlet. And, change the $Example_number variable to the example number you want to run. The command will fail if the example number is not valid.

This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable, -InformationAction, -InformationVariable, -OutBuffer, -OutVariable, -PipelineVariable, -ProgressAction, -Verbose, -WarningAction, and -WarningVariable. For more information, see about_CommonParameters.

You can pipe an object that represents the command to Invoke-Expression. Use the $Input automatic variable to represent the input objects in the command.

Returns the output that is generated by the invoked command (the value of the Command parameter).

• An expression is a statement that can be evaluated and produces a result, such as a Windows PowerShell command.

• Take reasonable precautions when using the Invoke-Expression cmdlet in scripts. When using Invoke-Expression to run a command that the user enters, verify that the command is safe to run before running it. In general, it is best to design your script with predefined input options, rather than allowing freeform input.