Powershell function returning an array instead of string

Question

i'm importing a csv and i would like to add a column to it (with the result based off of the previous columns)

my data looks like this

host address,host prefix,site
10.1.1.0,24,400-01

i would like to add a column called "sub site"

so I wrote this module but the problem is, the actual ending object is an array instead of string

function site {
    Param($s)
    $s -match '(\d\d\d)'
     return $Matches[0]
}

$csv = import-csv $file | select-object *,@{Name='Sub Site';expression= {site $_.site}}

if I run the command

PS C:\>$csv[0]

Host Address :10.1.1.0
host prefix  :24
site         :400-01
sub site     : {True,400}

when it should look like

PS C:\>$csv[0]

Host Address :10.1.1.0
host prefix  :24
site         :400-01
sub site     : 400

EDIT: I found the solution but the question is now WHY.

If I change my function to $s -match "\d\d\d" |out-null I get back the expected 400

The $s -match '(\d\d\d)' outputs True. That gets passed to the pipeline if you do not suppress it. — Lieven Keersmaekers
– Lieven Keersmaekers, Commented Nov 7, 2018 at 7:47
and fwiw - if you subsite is always 3 characters like your regex shows, following woud do without the need of an extra function *,@{Name='Sub Site';expression= {$_.site.SubString(0,3)}} — Lieven Keersmaekers
– Lieven Keersmaekers, Commented Nov 7, 2018 at 7:50
thanks, great idea. However my case is a bit more complicated then I actually posted so it isn't always at the front! — genx1mx6
– genx1mx6, Commented Nov 8, 2018 at 8:22

Kory Gill · Accepted Answer · 2018-11-07 07:51:47Z

3

Good you found the answer. I was typing this up as you found it. The reason is because the -match returns a value and it is added to the pipeline, which is all "returned" from the function.

For example, run this one line and see what is does:

"Hello" -match 'h'

It prints True.

Since I had this typed up, here is another way to phrase your question with the fix...

function site {
    Param($s)
    $null = $s -match '(\d\d\d)'
    $ret =  $Matches[0]

    return $ret
}

$csv = @"
host address,host prefix,site
10.1.1.1,24,400-01
10.1.1.2,24,500-02
10.1.1.3,24,600-03
"@

$data = $csv | ConvertFrom-Csv

'1 =============='
$data | ft -AutoSize

$data2 = $data | select-object *,@{Name='Sub Site';expression= {site $_.site}}

'2 =============='
$data2 | ft -AutoSize

answered Nov 7, 2018 at 7:51

Kory Gill

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1 Comment

genx1mx6 Over a year ago

Thanks, I also thought of another way and that's to take the last index of the array that gets returned so site $($_.site)[-1] However I think I like your solution more since you aren't guaranteed to get an array back from every function.

Bbb · Accepted Answer · 2023-12-01 15:23:36Z

1

This is one of the most idiotic things Powershell devs have ever done. In c# the language doesn't try to override the coders desires. This is so ridiculous.

Anyway you can put the entire function inside of @() | Out-Null, like so

function site {
    Param($s)
    {
    $s -match '(\d\d\d)'
    } | Out-Null;
    # custom object or string or whatever here
     return $Matches[0]
}

Some reading https://www.davemason.me/2021/11/29/powershell-functions-and-return-types

Function return value in PowerShell

edited Dec 1, 2023 at 15:23

answered Dec 1, 2023 at 14:43

Bbb

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