Invoke-Expression
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.
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-ExpressionThese 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 $CommandThis 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_codeThis 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: | String |
| Position: | 0 |
| Default value: | None |
| Required: | True |
| Accept pipeline input: | True |
| Accept wildcard characters: | False |
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.