为什么在 PowerShell 中使用逗号连接字符串？

Question

I have encountered a PowerShell behavior I don't understand. A comma between strings concatenates them and inserts a space in between, eg:

PS H:\> [string]$result = "a","b"

PS H:\> $result # a string with 3 characters
a b

If the result is interpeted as an array, then using a comma separates the elements of the array, eg:

PS H:\> [array]$result = "a","b"

PS H:\> $result # an array with 2 elements
a
b

I have tried searching for an explanation of this behavior, but I don't really understand what to search for. In the documentation about the comma operator , I see that it is used to initialize arrays, but I have not found an explanation for the "string concatenation" (which, I suspect, may not be the correct term to use here).

Answer 1

Indeed: , is the array constructor operator .

Since your variable is a scalar - a single [string] instance - PowerShell implicitly stringifies your array (converts it to a string).

PowerShell stringifies arrays by joining the (stringified) elements of the array with a space character as the separator by default.
You may set a different separator via the $OFS preference variable , but that is rarely done in practice. ^[1]

You can observe this behavior in the context of string interpolation :

PS> "$( "a","b" )"
a b

---

^{[1] As zett42 points out, an easier way to specify a different separator is to use the -join operator ; eg,
"a", "b" -join '@' yields 'a@b' .
By contrast, setting $OFS without resetting it afterwards can cause later commands that expect it to be at its default to malfunction; with -join you get explicit control.}