Powershell pass a range as an array?

Question

I'm trying to pass a range as an array so I can return an array in PowerShell:

function iterHostsToArray($arr, $str) {
   $hostz = @()
   $arr | % { $hostz = "$($str)$($_)" }
   return $hostz
}

$skybarHosts = iterHostsToArray((1..2), 'BAR')
$skyboxHosts = iterHostsToArray((1..6), 'BOX')

And I'm expecting the following:

PS> $skybarHosts
BAR1
BAR2

PS> $skyboxHosts
BOX1
BOX2
BOX3
BOX4
BOX5
BOX6

I'm refactoring from something like this, which works:

$skybarHosts = @()
(1..2) | % { $skybarHosts += "HCPNSKYBAR$($_)" }

You are overwriting the $hostz variable in each iteration. also, when a function should return an array, preceed that with a comma. This unary comma ensures the returned value is an array, even if it has just one element. — Theo
– Theo, Commented Jan 14, 2021 at 20:10

vonPryz · Accepted Answer · 2021-01-15 06:52:17Z

3

There are two issues. The first is a common pitfall in Powershell: function definitions use commas to separate parameters, but function calls use spaces. The syntax to pass a range and string is like so,

iterHostsToArray (1..2) 'BAR'

Another an issue is that the $hostz array is overwritten, not appended. Use += to append new elements into the array like so,

$hostz = @()
$arr | % { $hostz += "$($str)$($_)" }

As mentioned in comment, if all the function does is creation of an array, it can be simplified a bit. When the $arr is passed to a foreach iterator and no assignment is done, the output is passed along the pipeline and the function returns an array of objects. Like so,

function iterHostsToArray($arr, $str) {
    $arr | % {  "$($str)$($_)" }         
}

This approach, of course, doesn't work if you'd like to do work with the array contents within the function. In that case,

function iterHostsToArray($arr, $str) {
    $hostz = $arr | % {  "$($str)$($_)" }
    # Do sutff with $hostz
    # ...

    # finally, either
    return $hostz    
    # or simply
    $hostz 
}

edited Jan 15, 2021 at 6:52

answered Jan 14, 2021 at 20:06

vonPryz

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1 Comment

zett42 Over a year ago

Actually there is no need for the $hostz variable as PowerShell builds up the output array automatically, very efficiently: function iterHostsToArray($arr, $str) { $arr | % { "$str$_" } }.

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