using variable in PowerShell array element

Question

How to I add variables data inside the string element of an array? If I do $s.Length, the output is 1 instead of 2.

$IPAddress = '192.168.1.1'
[string[]]$s = (
    'https://google.com/' + $IPAddress + '/hostname',
    'https://google.com/' + $IPAddress + '/DNS'
)
foreach ($element in $s) {
    Write-Host $element
}

TheMadTechnician · Accepted Answer · 2017-08-22 23:11:50Z

2

The simplest way to accomplish what you are trying (string expansion) is:

$s = "https://google.com/$IPAddress/hostname",
        "https://google.com/$IPAddress/DNS"

By using double quotes it will automatically expand $IPAddress within the strings. This works best when the variable is a string, as more complex objects may not perform as expected. If you need to reference a property of an object in this manner you will need to wrap it in $(), for example "Hello $($User.Name)!" to expand the Name property of the $User object.

answered Aug 22, 2017 at 23:11

TheMadTechnician

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1 Comment

spunkyquagga Over a year ago

Thanks, that was very helpful!

Ansgar Wiechers · Accepted Answer · 2017-08-23 10:15:30Z

$s contains a single string because of the way you define the array. The concatenation operator (+) has a weaker precedence than the array construction operator (,). Because of that a statement

'foo' + $v + 'bar', 'foo' + $v + 'baz'

actually works like this:

'foo' + $v + @('bar', 'foo') + $v + 'baz'

Due to the string concatenation operation the array is mangled into a space-separated string (the separator is defined in the automatic variable $OFS), resulting in this:

'foo' + $v + 'bar foo' + $v + 'baz'

To avoid this behavior you need to either put the concatenation operations in grouping expressions:

$s = ('https://google.com/' + $IPAddress + '/hostname'),
     ('https://google.com/' + $IPAddress + '/DNS')

or inline the variables (requires double-quoted strings):

$s = "https://google.com/${IPAddress}/hostname",
     "https://google.com/${IPAddress}/DNS"

You could also use the format operator, but that requires grouping expressions as well:

$s = ('https://google.com/{0}/hostname' -f $IPAddress),
     ('https://google.com/{0}/DNS' -f $IPAddress)

Side note: Casting the variable to [string[]] is optional. Using the comma operator will give you an array even without an explicit cast.

andyb · Accepted Answer · 2017-08-23 05:32:49Z

1

TheMadTechnician beat me to it by a few seconds, but if you prefer to construct the string expressions explicitly, wrap them in parens:

$IPAddress = '192.168.1.1'
[string[]]$s = (
        ('https://google.com/'+$IPAddress+'/hostname'),
        ('https://google.com/'+$IPAddress+'/DNS'))
foreach ($element in $s) 
{
Write-Host $element
}

The parens force the expressions inside to be evaluated first.

edited Aug 23, 2017 at 5:32

answered Aug 22, 2017 at 23:21

andyb

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