Invoke-Expression
SYNOPSIS
Runs commands or expressions on the local computer.
SYNTAX
Invoke-Expression [-Command] <String> [<CommonParameters>]
DESCRIPTION
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 is returned (echoed) unchanged.
Expressions are evaluated and run in the current scope. For more information, see about_Scopes (../Microsoft.PowerShell.Core/About/about_Scopes.md).
> [!CAUTION] > 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.
EXAMPLES
Example 1: Evaluate an expression
$Command = "Get-Process"
$Command
Get-Process
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. PowerShell echoes the string.
The third command uses `Invoke-Expression` to evaluate the string.
Example 2: Run a script on the local computer
Invoke-Expression -Command "C:\ps-test\testscript.ps1"
"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`.
Example 3: Run a command in a variable
$Command = 'Get-Process | where {$_.cpu -gt 1000}'
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.
Example 4: Get and run a cmdlet Help example
$Cmdlet_name = "Get-ComputerInfo"
$Example_number = 1
$Example_code = (Get-Help $Cmdlet_name).examples.example[($Example_number-1)].code
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 `$Example_number` variable to the example number you want to run. The command fails if the example number is not valid.
> [!NOTE] > If the example code from the help file has output in the example, PowerShell attempts to run the > output along with the code and an error will be thrown.
PARAMETERS
-Command
Specifies the command or expression to run. Type the command or expression or enter a variable that contains the command or expression. The Command parameter is required.
Type: System.String
Parameter Sets: (All)
Aliases:
Required: True
Position: 0
Default value: None
Accept pipeline input: True (ByValue)
Accept wildcard characters: False
CommonParameters
This cmdlet supports the common parameters: -Debug, -ErrorAction, -ErrorVariable, -InformationAction, -InformationVariable, -OutVariable, -OutBuffer, -PipelineVariable, -Verbose, -WarningAction, and -WarningVariable. For more information, see about_CommonParameters.
INPUTS
System.String or PSObject
You can pipe an object that represents the command to `Invoke-Expression`. Use the `$Input` automatic variable to represent the input objects in the command.
OUTPUTS
PSObject
Returns the output that is generated by the invoked command (the value of the Command parameter).
NOTES
In most cases, you invoke expressions using PowerShell's call operator and achieve the same results. The call operator is a safer method. For more information, see about_Operators (../microsoft.powershell.core/about/about_operators.md#call-operator-).