Environment Variables, Processes, and Services

Environment variables

$env:APP_MODE = 'staging'
"Mode: $env:APP_MODE"
$null -eq $env:MISSING
Test-Path Env:APP_MODE
Remove-Item Env:APP_MODE
Test-Path Env:APP_MODE

Mode: staging
True
True
False

• $env:NAME reads and sets environment variables for the current session and the programs it starts.
• The Env: drive lets you use Get-ChildItem Env:, Test-Path, and Remove-Item on them.
• To set one permanently on Windows: [Environment]::SetEnvironmentVariable('NAME', 'value', 'User').

Processes

# illustrative
Get-Process | Sort-Object WorkingSet -Descending | Select-Object -First 5 Name, Id,
  @{ Name = 'MemoryMB'; Expression = { [math]::Round($_.WorkingSet / 1MB) } }

Start-Process notepad
Get-Process notepad | Stop-Process

Name      Id MemoryMB
----      -- --------
chrome  8124      612
Code   11220      498
Teams   6632      401
pwsh    9310      142
explorer 5204      118

Run an external program and wait for it, capturing its exit code:

# illustrative
$p = Start-Process -FilePath 'msiexec.exe' -ArgumentList '/i app.msi /quiet' -Wait -PassThru
$p.ExitCode

Console programs can also be called directly (git status); their exit code is in $LASTEXITCODE.

Services (Windows)

# illustrative
Get-Service -Name Spooler
Get-Service | Where-Object { $_.Status -eq 'Stopped' -and $_.StartType -eq 'Automatic' }
Restart-Service -Name Spooler -WhatIf
Set-Service -Name Spooler -StartupType Manual

Changing services requires an elevated (Run as administrator) session. On Linux, manage services with systemctl, called from PowerShell like any other program.

The registry (Windows)

The registry is exposed as drives, so the file cmdlets work on it:

# illustrative
Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' |
  Select-Object ProductName, DisplayVersion
New-ItemProperty -Path 'HKCU:\Software\MyApp' -Name Theme -Value dark