Powershell - “Expressions are only allowed as the first element of a pipeline”

问题

Could someone please tell me how to avoid this error in the below circumstance?

$codegenDir = "Z:\Desktop\Song-Renamer"
$PowerShellRepresentation = dir -path $MyMusicFolder -recurse -include *.mp3,*.m4a,*.wma,*.flac,*.ape | select -ExpandProperty FullName | $codegenDir\codegen.exe -s 10 20 | Out-String | ConvertFrom-Json

What completely puzzles me is if simply omit $codegenDir (see below), the code operates correctly. I "think" I understand the concept of placing the expression first (ahead of other items in the pipeline. But I'm not sure how to rearrange/split this code so the expression in question the Codegen.exe external commandline is the first item in the pipeline (and still be able to pass data to it via pipeline).

$PowerShellRepresentation = dir -path $MyMusicFolder -recurse -include *.mp3,*.m4a,*.wma,*.flac,*.ape | select -ExpandProperty FullName | .\codegen.exe -s 10 20 | Out-String | ConvertFrom-Json

Ideally, it would be nice to do this using the least amount of code as possible.

回答1:

Give the following a shot (only difference is the &):

$PowerShellRepresentation = dir -path $MyMusicFolder -recurse -include *.mp3,*.m4a,*.wma,*.flac,*.ape | select -ExpandProperty FullName | & $codegenDir\codegen.exe -s 10 20 | Out-String | ConvertFrom-Json

Here's a link to a technet article about executing commands in powershell in different ways.

来源：https://stackoverflow.com/questions/23034328/powershell-expressions-are-only-allowed-as-the-first-element-of-a-pipeline