Install git-cleanup in your PowerShell profile: iex (irm 'https://gist.githubusercontent.com/jongalloway/8e983bf0d761826f8deacf84e2660c07/raw/install-git-cleanup.ps1')

install-git-cleanup.ps1

$profilePath = $PROFILE.CurrentUserCurrentHost
$functionPattern = '(?m)^\s*function\s+git-cleanup\b'

if (Test-Path -LiteralPath $profilePath) {
    $profileContent = Get-Content -LiteralPath $profilePath -Raw
    if ($profileContent -match $functionPattern) {
        Write-Host "git-cleanup is already defined in $profilePath"
        return
    }
}

$profileDirectory = Split-Path -Parent $profilePath
if (-not (Test-Path -LiteralPath $profileDirectory)) {
    New-Item -ItemType Directory -Path $profileDirectory -Force | Out-Null
}

$gitCleanupFunction = @'

# Removes local branches whose remote tracking branch has been deleted.
function git-cleanup {
    git fetch --prune
    git branch -vv | ForEach-Object {
        if ($_ -match '^\s+(\S+)\s+\S+\s+\[.+: gone\]') {
            git branch -D $matches[1]
        }
    }
}
'@

[System.IO.File]::AppendAllText(
    $profilePath,
    $gitCleanupFunction,
    [System.Text.UTF8Encoding]::new($false)
)

Invoke-Expression $gitCleanupFunction
Write-Host "Added git-cleanup to $profilePath"