Powershell通过管道传递路径时的连接路径错误

Question

Join-Path allegedly accepts the Path parameter from the pipeline.

This suggests that the two functions below should both work alike:

join-path 'c:\temp' 'x'     #returns c:\temp\x
'c:\temp' | join-path 'x'   #throws an error

However the second call (ie using passing the Path parameter by value to the pipeline) gives the below error:

join-path : The input object cannot be bound to any parameters for the command either because the command does not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input. At line:1 char:13 + 'c:\\temp' | join-path 'x' + ~~~~~~~~~~~~~ + CategoryInfo : InvalidArgument: (c:\\temp:String) [Join-Path], ParameterBindingException + FullyQualifiedErrorId : InputObjectNotBound,Microsoft.PowerShell.Commands.JoinPathCommand

NB: Since path may be an array I also tried [array]('c:\\temp') | join-path 'x' [array]('c:\\temp') | join-path 'x' ; but this made no difference.

Have I misunderstood something, or is this a bug in PowerShell?

Answer 1

In your first example, an expression join-path 'c:\\temp' 'x' is interpreted by PowerShell as Join-Path -Path 'c:\\temp' -ChildPath 'x' (because the names for positional parameters Path and ChildPath are optional).

In your second example, you are passing a pipeline parameter 'c:\\temp' to the command Join-Path -Path 'x' (not the absence of ChildPath parameter). It will not work because Join-Path accepts only Path parameter from the pipeline but you have already defined it.

If you want to bind another , not first parameter, you should write it name explicitly, as in

'c:\temp' | Join-Path -ChildPath 'x'
# => 'c:\temp\x'