Powershell: how to read an environment variable?

Question

This is the first powershell script I have attempted. When I run it, part one runs fine and creates the log.txt, but after running it again it still runs part 1. How can I check if the log file exists??

EDIT: I forgot to mention that I am running the script from PowerShell ISE if that makes a difference.

#Variables.
#Set working directory to scripts location.
$scriptpath = $MyInvocation.MyCommand.Path
$dir = Split-Path $scriptpath

#Check if log file exists.
$ChkFile = "%userprofile%\Desktop\log.txt" 
$FileExists = (Test-Path $ChkFile -PathType Leaf)

#Set dir to script location.
Set-Location $dir

#Part 1.
If (!($FileExists)) 
{
    Write-Host "Part 1"
    echo 0 >>log.txt
}
#Part 2.
ElseIf ($FileExists)
{
    Write-Host "Part 2"
}

Andy Arismendi · Accepted Answer · 2012-05-31 22:46:10Z

7

% is for cmd.exe variable expansion. You need a different syntax for PowerShell. Instead use:

 "$env:userprofile\Desktop\log.txt"

answered May 31, 2012 at 22:46

Andy Arismendi

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4 Comments

arynhard Over a year ago

Thank you. That fixed it. Do all cmd.exe commands not work in powershell?

Andy Arismendi Over a year ago

@AndrewRynhard If the command is implemented with cmd.exe then it will not work in PowerShell unless you invoke it via & cmd.exe /c <DOS COMMAND HERE>. If the command is actually a command line program like xcopy it will work fine in PowerShell.

Michael Sorens Over a year ago

Andy is spot on for commands, but the percent (%) indicator falls under a different, though like-minded, rule: if the feature is implemented by cmd.exe then you must find the analogous feature in PowerShell. In this instance, %xyz% indicates an environment variable under cmd.exe, while $env:xyz indicates the same env var in PowerShell.

Andy Arismendi Over a year ago

@msorens Actually you can pass in cmd.exe operators. Try these: & cmd.exe /c echo '%userprofile%\Desktop\log.txt' and & cmd.exe /c dir '"%ProgramFiles%"' '&' dir '"%windir%"'. They just get sent as strings to cmd.exe which evaluates them at runtime.

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