Array index from first to second last in PowerShell

Question

How can I get the array element range of first to second last?

For example,

$array = 1,2,3,4,5
$array[0] - will give me the first (1)
$array[-2] - will give me the second last (4)
$array[0..2] - will give me first to third (1,2,3)
$array[0..-2] - I'm expecting to get first to second last (1,2,3,4) but I get 1,5,4 ???

I know I can do long hand and go for($x=0;$x -lt $array.count;$x++) , but I was looking for the square bracket shortcut.

Answer 1

You just need to calculate the end index, like so:

$array[0..($array.length - 2)]

Do remember to check that you actually have more than two entries in your array first, otherwise you'll find yourself getting duplicates in the result.

An example of such a duplicate would be:

@(1)[0..-1]

Which, from an array of a single 1 gives the following output

1 
1

Answer 2

As mentioned earlier the best solution here: $array[0..($array.length - 2)]

The problem you met with $array[0..-2] can be explained with the nature of "0..-2" expression and the range operator ".." in PowerShell. If you try to evaluate just this part "0..-2" in PowerShell you will see that result will be an array of numbers from 0 to -2.

>> 0..-2
0
-1
-2

And when you're trying to do $array[0..-2] in PowerShell it's the same as if you would do $array[0,-1,-2] . That's why you get results as 1, 5, 4 instead of 1, 2, 3, 4 .

It could be kind of counterintuitive at first especially if you have some Python or Ruby background, but you need to take it into account when using PowerShell.

Answer 3

There might be a situation where you are processing a list, but you don't know the length. Select-object has a -skiplast parameter.

(1,2,3,4,5 | select -skiplast 2)

1
2
3

Answer 4

Robert Westerlund answer is excellent. This answer I just saw on the Everything you wanted to know about arrays page and wanted to try it out. I like it because it seems to describe exactly what the goal is, end at one short of the upper bound.

$array[0..($array.GetUpperBound(0) - 1)]
1
2
3
4

I used this variation of your original attempt to uninstall all but the latest version from Get-InstalledModule. It's really short, but not perfect because if there are more than 9 items it still returns just 8, but you can put a larger negative number, though.

$array[-9..-2]
1
2
3
4