此功能为我完成了工作：

function Join-PathOrAbsolute ($Path, $ChildPath) {
    if (Split-Path $ChildPath -IsAbsolute) {
        Write-Verbose ("Not joining '$Path' with '$ChildPath'; " +
            "returning the child path as it is absolute.")
        $ChildPath
    } else {
        Write-Verbose ("Joining path '$Path' with '$ChildPath', " +
            "child path is not absolute")
        Join-Path $Path $ChildPath
    }
}

# short version, without verbose messages:

function Join-PathOrAbsolute ($Path, $ChildPath) {
  if (Split-Path $ChildPath -IsAbsolute) { $ChildPath }
  else { Join-Path $Path $ChildPath }
}

Join-PathOrAbsolute C:\code .\out  # => C:\code\.\out (just the Join-Path output)
Join-PathOrAbsolute C:\code\ D:\   # => D:\ (just the $ChildPath as it is absolute)

它只是检查后一个路径是否是绝对路径，如果是绝对路径则返回它，否则它仅Join-Path在$Path和两者上运行$ChildPath。请注意，这并不认为基础$Path是相对的，但是对于我的用例而言，这已经足够了。（我(Get-Item -Path './').FullName用作基本路径，无论如何都是绝对路径。）

Join-PathOrAbsolute .\ D:\    # => D:\
Join-PathOrAbsolute .\ .\out  # => .\.\out

请注意，虽然.\.\和C:\code\.\out确实看起来很怪异，它是有效的，并解决的正确路径。Join-Path毕竟，这只是PowerShell集成功能的输出。