Why my PowerShell script is not respecting the ste

问题:

This question already has an answer here:

• Unable to Pause or Sleep after Select-Object 2 answers

I tried to find the solution by myself but now I'm out of ideas. I wrote a script that I want to use to check if Erlang is installed on a machine:

# Check if a Software ins installed
function Check_Program_Installed($programName) {
$x86_check = ((Get-ChildItem "HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall") |
Get-ItemProperty |
        Where-Object {$_.DisplayName -like "*$programName*" } |
            Select-Object -Property DisplayName, UninstallString)

if(Test-Path 'HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall')  
{
$x64_check = ((Get-ChildItem "HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall") |
Get-ItemProperty |
        Where-Object {$_.DisplayName -like "*$programName*" } |
            Select-Object -Property DisplayName, UninstallString)
}
if ($x86_check -and $x64_check -eq $null){ 
    write-host "$programName is not installed on this computer" -ForegroundColor Green 
    #continue
    }
elseif ($x86_check -or $x64_check -ne $null){
    write-host "On this computer is installed " -ForegroundColor Red     
    $x86_check
    $x64_check

    }
}

# Erlang check
Write-Host "Checking if Erlang exist    " -NoNewline
Check_Program_Installed("Erlang")

Write-Host "The End: the script ends here" -ForegroundColor Yellow

But if I execute it as result the very last line is executed before Check_Program_Installed("Erlang"). Why PowerShell is not respecting the step priority?

Checking if Erlang exist        On this computer is installed

The End: the script ends here
DisplayName          UninstallString
-----------          ---------------
Erlang OTP 21 (10.2) C:\Program Files\erl10.2\Uninstall.exe

回答1:

Just add Format-Table to $x86_check and $64_check at the end. Link to answer: https://social.technet.microsoft.com/Forums/en-US/5f88f7c9-fbce-4c45-a2fa-806d512a0233/powershell-output-wrong-order?forum=ITCG

# Check if a Software ins installed
function Check_Program_Installed($programName) {
$x86_check = ((Get-ChildItem "HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall") |
Get-ItemProperty |
        Where-Object {$_.DisplayName -like "*$programName*" } |
            Select-Object -Property DisplayName, UninstallString) | Format-Table

if(Test-Path 'HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall')  
{
$x64_check = ((Get-ChildItem "HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall") |
Get-ItemProperty |
        Where-Object {$_.DisplayName -like "*$programName*" } |
            Select-Object -Property DisplayName, UninstallString) | Format-Table
}
if ($x86_check -and $x64_check -eq $null){ 
    write-host "$programName is not installed on this computer" -ForegroundColor Green 
    #continue
    }
elseif ($x86_check -or $x64_check -ne $null){
    write-host "On this computer is installed " -ForegroundColor Red     
    $x86_check
    $x64_check

    }

}

# Erlang check
Write-Host "Checking if Erlang exist    " -NoNewline
Check_Program_Installed("Erlang")
Write-Host "The End: the script ends here" -ForegroundColor Yellow

回答2:

I have tried copying your code and testing it, however I cannot make the actual Check_Program_Installed function work, so it is hard for me to validate.

However, for PowerShell it is important to understand the pipeline.

Normally with everything you do, it is send to the pipeline and will appear in your console in the order that the pipeline got it.

However Write-Host does not send your text to the pipeline, it sends it directly to the console, so it could be a simple race condition where the text gets to the console faster than the pipeline object.

If you try to test using Write-Output instead of Write-Host I would guess you get it in the correct order, since Write-Output sends an object to the console through the pipeline.