python 版本切换脚本（pvm.ps1）

$path = "C:\apps\develop\sdks\python"
$content = "
    Usage:
        pvm help                   show the usage of pvm
        pvm using                  show the python version in use
        pvm list                   show all version
        pvm use <version>          switch version
"
function ListVersion {
    # 将前缀是v的文件过滤出来
    Get-Item ($path + "\v*") | ForEach-Object { $_.Name }
}
function UseVersion ($version ) {
    $arguments = "New-Item -ItemType SymbolicLink -Path '$path\current' -Target '$path\$version' -Force"
    $user = [Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()
    if (-NOT ($user).IsInRole([Security.Principal.WindowsBuiltInRole] "Administrator")) {  
        Start-Process powershell -Verb runAs -ArgumentList $arguments
        return
    } 
    # Invoke-Expression 将字符串解析成命令执行
    Invoke-Expression $arguments
}
switch ($args[0]) {
    "help" { $content }
    "using" { 
        if (-not (Test-Path "$path\current")) {
            Write-Host "Please execute the use command first"
            exit
        }
        python --version
    }
    "list" { ListVersion }
    "use" { 
        if ($null -eq $args[1]) {
            $content
            exit
        }
        $version = $args[1].ToString().ToLower();
        if (-not $version.StartsWith("v")) {
            $version = "v$version"
        }
        if ((ListVersion) -contains $version) {
            UseVersion $version
        }
        else {
            Write-Host "No matching version"
        }
    }
    Default { $content }
}