How to prepend a "string" to a "string[]" variable? - powershell

Question

Let's suppose I have a PowerShell function that returns a [string[]]:
function do_something() {
[string[]]$str_array = #("one", "two", "three")
return $str_array
}
$x = do_something()
# doesn't work
$y = #("something", $x)
Now I want to prepend a string to the front of the [string[]] list.
How would I go about doing that?

Answer 1

There are several ways to join two arrays. Regarding your question in the above comment:
That's interesting, I wasn't aware that a "," is different from a ";" when forming a list...
In PowerShell, the , is an own operator, where its behavior differs if used in a unary or binary statement.
From about_operators:
As a binary operator, the comma creates an array. As a unary operator, the comma creates an array with one member. Place the comma before the member.
In the code #("something", $x) you're using the operator in binary form. So a new array with two entries is created. The first entry is the string "something", the second entry contains an array of strings. Thats because PowerShell interprets it as: "Ok, I shall create a new array with two entries (="something", and a reference pointing to an array).
We can check that with the help or Get-Member:
C:\> $y | Get-Member
TypeName: System.String
Name MemberType Definition
---- ---------- ----------
Clone Method System.Object Clone(), System.Object ICloneable.Clone()
...
TypeName: System.Object[]
Name MemberType Definition
---- ---------- ----------
Add Method int IList.Add(System.Object value)
...
As can be seen, Get-Member shows use two TypeNames. The first is a string, the second is an array.
When changing the code to #("something"; $x) no ,-operator is used anymore. Instead, the code is now split up in about three "command", since the command-separator (=;) is used.
Cmd1: "something"
Cmd2: $x -> which dumps the array content
Cmd3: #() -> guarantees that the expressions inside the brackets are returned as an array.
You can also remove the command seperator and define $y over multiple lines:
PS C:\>$y = #("something"
>>> $x
>>> )
The be less ambiguous I'd recommend to merge two arrays in the following way:
PS C:\> $a = 1
PS C:\> $b = #(2,3,4)
PS C:\> $c = #()
PS C:\> $c += $a
PS C:\> $c += $b
PS C:\> $c
1
2
3
4
PS C:\> $c | gm
TypeName: System.Int32
Name MemberType Definition
...
Of course, it's "more" code, but its less ambiguous.
Hope that helps.