如何将PowerShell命令的输出用作另一个PowerShell命令的参数？

Question

我想要折叠这些PowerShell命令：

$colour = ""
$colour1 = "Red"
$colour2 = "Green"
if ($var -eq 0) {
    # failure
    $colour = $colour1
} Else {
    # success
    $colour = $colour2
}
Write-Host ("Answer = " + $var) -ForegroundColor $colour

将上面的if表达式的输出作为Write-Host的输入参数，合并成一行，类似于：

Write-Host ("Answer = " + $var) -ForegroundColor &{if ($var -eq 0) {'Red'} else {'Green'}

我尝试过但失败了的事情：

Write-Host ("Answer = " + $var) -ForegroundColor &{if ($var -eq 0) {'Red'} else {'Green'}
Write-Host ("Answer = " + $var) -ForegroundColor `&{if ($var -eq 0) {'Red'} else {'Green'}`
Write-Host ("Answer = " + $var) -ForegroundColor `{if ($var -eq 0) {'Red'} else {'Green'}`
Write-Host ("Answer = " + $var) -ForegroundColor &`{if ($var -eq 0) {'Red'} else {'Green'}`
Write-Host ("Answer = " + $var) -ForegroundColor (&`{if ($var -eq 0) {'Red'} else {'Green'}`)
Write-Host ("Answer = " + $var) -ForegroundColor `{if ($var -eq 0) {return 'Red'} else {return 'Green'}`
Write-Host ("Answer = " + $var) -ForegroundColor `&{if ($var -eq 0) {return 'Red'} else {return 'Green'}`
Write-Host ("Answer = " + $var) -ForegroundColor `&{if ($var -eq 0) {return "Red"} else {return "Green"}`
Write-Host ("Answer = " + $var) -ForegroundColor &{if ($var -eq 0) {return "Red"} else {return "Green"}
Write-Host ("Answer = " + $var) -ForegroundColor &{if ($var -eq 0) {return "Red"} else {return "Green"}}
Write-Host ("Answer = " + $var) -ForegroundColor `&{if ($var -eq 0) {return "Red"} else {return "Green"}}`
Write-Host ("Answer = " + $var) -ForegroundColor &`{if ($var -eq 0) {return "Red"} else {return "Green"}}`
Write-Host ("Answer = " + $var) -ForegroundColor `{if ($var -eq 0) {return "Red"} else {return "Green"}}`
Write-Host ("Answer = " + $var) -ForegroundColor `if ($var -eq 0) {return "Red"} else {return "Green"}`

- skeetastax

Answer 1

要将整个语句（如if）的输出作为命令参数传递，请使用$(...)，即子表达式运算符。

一个简化的例子：

# Note the use of $(...) around the `if` statement.
PS> $var = 0; Write-Host $(if ($var -eq 0) { 'zero' } else { 'nonzero' })
zero

请注意，如果只需要表达式或命令的输出，则使用分组运算符(...)即可（并且无副作用）。

例如，PowerShell（Core）7+中替代if语句的是三元运算符，其使用是一个表达式。

# PowerShell (Core) 7+ only.
# Since an expression is used, (...) is sufficient.
PS> $var = 0; Write-Host ($var -eq 0 ? 'zero' : 'nonzero')
zero

对于命令（管道），(...) 也是足够的。

# Since a command is used, (...) is sufficient.
Write-Output (Get-Item *.txt | Where-Object Length -ge 1kb)

---

有关$(...)与(...)的更多信息，请参见this answer。

- mklement0

---

@skeetastax，这是因为您输错了-ForegroundColor（缺少e），所以参数名称无法识别，-ForgroundColor被视为另一个位置参数来打印。换句话说：您的问题是偶然的，而这个答案仍然适用。 - undefined

@skeetastax :) 犯这种错误很容易。很高兴听到它起作用了。 - undefined