Running External Executables from PowerShell

PowerShell is a powerful scripting language for task automation and configuration management. Often, you’ll need to execute programs that weren’t specifically designed for PowerShell, like command-line tools or applications built for the traditional command prompt (CMD). This tutorial explains how to run these external executables reliably from within your PowerShell scripts.

Understanding the Challenges

PowerShell and CMD handle commands differently. CMD directly interprets commands as internal operations or searches for them in the system’s PATH environment variable. PowerShell, on the other hand, treats everything as objects and commands (called cmdlets) are typically .NET methods. Directly passing a string containing a CMD command to PowerShell won’t necessarily execute it as expected.

Methods for Executing External Programs

There are several ways to run external executables from PowerShell, each with its own advantages and considerations:

1. Direct Execution (If in PATH)

If the executable is located in a directory listed in your system’s PATH environment variable, you can often run it directly by typing its name:

CmRcViewer.exe PCNAME

PowerShell will search the PATH for CmRcViewer.exe and, if found, execute it with the argument PCNAME. This is the simplest method but relies on the program being correctly registered in the PATH.

2. Using the Call Operator (&)

The call operator (&) is the preferred method for executing commands stored in variables or strings. This tells PowerShell to treat the string as a command to be executed.

$command = "C:\Program Files (x86)\Microsoft Configuration Manager\AdminConsole\bin\i386\CmRcViewer.exe"
& $command PCNAME

This approach is more robust than direct execution because it allows you to construct the command dynamically and handle paths with spaces or special characters. The & operator is essential when the command is stored in a variable.

3. Using cmd.exe /c

You can leverage the command prompt itself to execute commands. This is useful when you need to run a batch script or a complex CMD command.

cmd.exe /c "C:\Program Files (x86)\Microsoft Configuration Manager\AdminConsole\bin\i386\CmRcViewer.exe PCNAME"

The /c switch tells cmd.exe to execute the specified command and then terminate. This method is reliable but introduces the overhead of launching a new CMD process.

4. Using Start-Process

The Start-Process cmdlet provides more control over how the external process is launched. You can specify arguments, working directory, and other parameters.

Start-Process "C:\Program Files (x86)\Microsoft Configuration Manager\AdminConsole\bin\i386\CmRcViewer.exe" -ArgumentList "PCNAME"

-ArgumentList is used to pass arguments to the executable. Start-Process is particularly useful when you need to monitor the process or interact with its output. It also allows you to specify window styles or run the process in the background.

Best Practices

Use the Call Operator (&) for Dynamic Commands: When constructing commands dynamically from variables, always use the call operator (&).
Fully Qualify Paths: To avoid ambiguity, provide the full path to the executable.
Handle Spaces in Paths: If the path contains spaces, enclose it in double quotes.
Consider Start-Process for Advanced Control: For scenarios where you need to manage the process lifecycle, use Start-Process.
Check Exit Codes: Always check the exit code of the external process to determine if it executed successfully. You can access the exit code using the $LastExitCode variable.

By understanding these methods and following these best practices, you can seamlessly integrate external executables into your PowerShell scripts and automate complex tasks effectively.