这个迭代 List 的 powershell 脚本有什么问题？ Foreach-Object -Process { 设置别名 ... }

Question

I have got a module that returns a List of LinuxAlias (class I made)

When I try to iterate them to Set-Alias in my session I am having troubles.

Data: MyModule has the Get-LinuxAliases command. Get-LinuxAliases command is a binary module that returns a List of LinuxAlias.

Output definition:

[OutputType(typeof(List<LinuxAlias>))]

LinuxAlias definition:

public class LinuxAlias
    {
        public String Name { get; set; }
        public String RawCommand { get; set; }

        public String Value { get; set; }
        public String TranslatedPowershellCommand { get; set; }
        public class COMMENT_BLOCK_EXCEPTION : Exception
        {
        }
        public class EMPTY_LINE_EXCEPTION : Exception
        {
        }
        public class UNRECOGNIZED_INPUT : Exception
        {
        }
    }

I do:

if ( Get-Module "MyModule" ) {
    Get-LinuxAliases | ForEach-Object -Process { 
        try {
            [string]$name = $_.Name;
            [string]$val = $_.Value;
                Set-Alias -Name $name -Value $val -Force;
        }
        catch {
            Write-Warning $_.Exception.GetType().FullName;
        }

    }
}

What is the expected behaviour? Since I noticed, for example. If I just Write-Host $_.Name and Write-Host $_.Value for each iteration. It first will write names and then values, having something like:

name1 name2 ... value1 value2 ...

What is not the expected behaviour in a For-Each iterator I guess. It should be:

name1 value1 name2 value2

(Get-LinuxAliases) [0] returned :

Name RawCommand Value TranslatedPowershellCommand
---- ---------- ----- ---------------------------
cls  'clear'    clear

Someone could bring me light to this scenario?

Thanks in advance.

Answer 1

that returns a List of LinuxAlias.

Generally, except in special circumstances, cmdlets :

• should not output instances of a collection type (such as List in your case).
• instead should output multiple objects to the pipeline one by one .

The reason is that other cmdlets - such as ForEach-Object - expect other commands to produce output object by object .

Get-LinuxAliases | ForEach-Object -Process { ...

With your current design, ForEach-Object receives a single input object that is the list as a whole , which is not your intent.

Therefore:

• Make your cmdlet-implementing class indicate that it returns LinuxAlias , not a list of it; that multiple instances of that type may be returned is invariably implied in PowerShell.

   [OutputType(typeof(LinuxAlias)]

• To produce output from your cmdlet, use WriteObject(list, true) , ie, use the WriteObject overload that enumerates collections ; that is, make it send the LinuxAlias instances stored in your List instance to the pipeline one by one .