Expression | Easy Powershell 2.0 Reference

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 would be returned (echoed) unchanged.

PARAMETERS
-Command <string>
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.

        Required?                    true
        Position?                    1
        Default value
        Accept pipeline input?     true (ByValue)
        Accept wildcard characters? false

    <CommonParameters>
        This cmdlet supports the common parameters: Verbose, Debug,
        ErrorAction, ErrorVariable, WarningAction, WarningVariable,
        OutBuffer and OutVariable. For more information, type,
        “Get-Help 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

— 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.

————————– EXAMPLE 1 ————————–

C:\PS>$command = “Get-Process”

C:\PS> $command
Get-Process

C:\PS> 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
    …

    Description
    ———–
    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.

————————– EXAMPLE 2 ————————–

C:\PS>Invoke-Expression -Command “C:\ps-test\testscript.ps1”

C:\PS> “C:\ps-test\testscript.ps1” | Invoke-Expression

    Description
    ———–
    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 ————————–

C:\PS>$cmd = ‘Get-Process | where {$_.cpu -gt 1000}’

C:\PS> iex $command

    Description
    ———–
    This example runs a command string that is saved in the $cmd 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 string.

————————– EXAMPLE 4 ————————–

C:\PS>$cmdlet_name = “Get-Eventlog”

C:\PS> $example_number = 1

C:\PS> $example_code = (Get-Help $cmdlet_name).examples.example[($example_number-1)].code

C:\PS> Invoke-Expression $example_code

    Description
    ———–
    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.

RELATED LINKS
Online version: http://go.microsoft.com/fwlink/?LinkID=113343
Invoke-Command