Question

Noob help please. I’m trying to write a script that will check if a process is running, and if not, start it. If the process is running, it should do nothing. I’ve come up with the following so far but it is starting a new instance of the process regardless of whether it was running already. Any help is appreciated.

$Prog = "C:\utilities\prog.exe"
$Running = Get-Process prog -ErrorAction SilentlyContinue
$Start = ([wmiclass]"win32_process").Create($Prog)
if($Running -eq $null)
{$Start}
else
{}

Answer 1

First of all, here’s is what is wrong in your code.
In your code, the process is created before you evaluate whether your program is already running

$Prog = "C:\utilities\prog.exe"
$Running = Get-Process prog -ErrorAction SilentlyContinue
$Start = ([wmiclass]"win32_process").Create($Prog) # the process is created on this line
if($Running -eq $null) # evaluating if the program is running
{$Start}

It is possible to create a block of code that should be evaluated further in your code by wrapping it in {} (a scriptblock):

$Prog = "C:\utilities\prog.exe"
$Running = Get-Process prog -ErrorAction SilentlyContinue
$Start = {([wmiclass]"win32_process").Create($Prog)} 
if($Running -eq $null) # evaluating if the program is running
{& $Start} # the process is created on this line

However, if you’re looking for a short one-liner to solve your problem:

if (! (ps | ? {$_.path -eq $prog})) {& $prog}