在 Powershell 中为变量设置默认值

问题描述

在 bash 中，如果 UserName 未设置，我可以这样做将 name 设置为默认值:

In bash I can do something like this to set name to a default value if UserName is not set:

name=${UserName:-James}

Powershell 是否支持这样的功能?

Does Powershell support something like this?

推荐答案

使用函数和参数，我们可以做一些我相信你正在做的事情.

Using functions and parameters we can do something like what I believe you are doing.

函数示例:

function WriteUser
{
    param($user = "A User",
    $message = "Message")
    Write-Host $user
    Write-Host $message
}

不带参数调用函数

WriteUser

会给你输出:

用户

留言

WriteUser -user 我"-消息错误"

WriteUser -user "Me" -message "Error"

会写以下内容:

我

错误

一些额外的注意事项，您不必使用参数名称.

A couple extra notes, you do not have to use the parameter names.

WriteUser "Bob" "All Systems Go" would work by the order of the parameters.

您也可以切换命名参数的顺序:

You can switch the order of the named parameters as well:

WriteUser -message "Error" -user "user, user"

该函数会将 放入正确的参数中.

and the function will put the to the correct parameter.

否则，我相信您必须做一些事情来近似三元行为，例如:

Otherwise, I believe you would have to do something to approximate ternary behavior like:

function Like-Tern
{
    for ($i = 1; $i -lt $args.Count; $i++)
    {
        if ($args[$i] -eq ":")
        {
            $coord = $i
            break
        }
    }

    if ($coord -eq 0) { throw new System.Exception "No operator!" }
    $toReturn
    if ($args[$coord - 1] -eq "")
    {
        $toReturn = $args[$coord + 1]
    }
    else
    {
        $toReturn = $args[$coord -1]
    }

    return $toReturn
}

此创意的功劳函数文件还可以包括:

Set-Alias ~ Like-Tern -Option AllScope

然后你会像这样使用它:

And then you would use it like:

$var = ~ $Value : "Johnny"

当然，~ 完全是随意的，因为我无法让 ${ 工作......

Of course, ~ was completely arbitrary because I couldn't get ${ to work...

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