Best way to join parts with a separator in PowerShell

Question

I need to join multple Url elements into one string, so I wrote the generic Join-Parts function:

filter Skip-Null { $_|?{ $_ } }

function Join-Parts
{
    param
    (
        $Parts = $null,
        $Separator = ''
    )

    [String]$s = ''
    $Parts | Skip-Null | ForEach-Object {
        $v = $_.ToString()
        if ($s -ne '')
        {
            if (-not ($s.EndsWith($Separator)))
            {
                if (-not ($v.StartsWith($Separator)))
                {
                    $s += $Separator
                }
                $s += $v
            }
            elseif ($v.StartsWith($Separator))
            {
                $s += $v.SubString($Separator.Length)
            }
        }
        else
        {
            $s = $v
        }
    }
    $s
}

Join-Parts -Separator '/' -Parts 'http://mysite','sub/subsub','/one/two/three'
Join-Parts -Separator '/' -Parts 'http://mysite',$null,'one/two/three'
Join-Parts -Separator '/' -Parts 'http://mysite','','/one/two/three'
Join-Parts -Separator '/' -Parts 'http://mysite/','',$null,'/one/two/three'
Join-Parts 1,2,'',3,4

Which returns as expected:

http://mysite/sub/subsub/one/two/three
http://mysite/one/two/three
http://mysite/one/two/three
http://mysite/one/two/three
1234

I have the feeling that this is not the smartest approach. Any ideas on a better approach?

UPDATE

Based on the answer by @sorens I changed the function into:

function Join-Parts
{
    param
    (
        $Parts = $null,
        $Separator = ''
    )

    ($Parts | ? { $_ } | % { ([string]$_).trim($Separator) } | ? { $_ } ) -join $Separator 
}

Have you considered a URIBuilder ?

Andy Arismendi
– Andy Arismendi

2012-03-06 23:31:36 +00:00
Commented Mar 6, 2012 at 23:31 — Andy Arismendi
– Andy Arismendi, Commented Mar 6, 2012 at 23:31

Michael Sorens · Accepted Answer · 2012-03-08 17:46:19Z

9

Building on the answer from @mjolinor this one-liner passes all the tests in your question:

($parts | ? { $_ } | % { ([string]$_).trim('/') } | ? { $_ } ) -join '/'

If you do not really care about the last test case (1,2,'',3,4) and can assume all inputs are strings you can shorten that to:

($parts | ? { $_ } | % { $_.trim('/') } | ? { $_ } ) -join '/'

Note that I have two null/empty filters (? { $_ } ) present: the first strips nulls or empty strings from the input, which rectifies your test case with an empty string ('http:/fdfdfddf','','aa/bb'). The second is also necessary, catching input reduced to empty by the trim function.

If you really want to be fastidious about it, you should add one more trim to eliminate whitespace-only values since those are likely unwanted:

($parts | ? { $_ } | % { $_.trim('/').trim() } | ? { $_ } ) -join '/'

With this last one these test case inputs will also return http://mysite/one/two:

$parts = 'http://mysite',''     ,'one/two' # empty
$parts = 'http://mysite','     ','one/two' # whitespace
$parts = 'http://mysite','    /','one/two' # trailing virgule
$parts = 'http://mysite','/    ','one/two' # leading virgule
$parts = 'http://mysite','/   /','one/two' # double virgule

answered Mar 8, 2012 at 17:46

Michael Sorens

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5 Comments

Michael Sorens Over a year ago

@SergevandenOever, now you have me wondering:-) you had accepted my answer months ago and now you have switched to a different answer also from months ago. And yet, mjolinar's answer passes only two of the five test cases in your question, while mine passes all five. Did I miss something ?

Serge van den Oever Over a year ago

you are absolutely right! I was checking questions I didn't give an answer to on a small screen, overlooked I already accepted your answer! I switched it back! Sorry:-)

Migol Over a year ago

I downvoted this solution for one very important reason: READABILITY. This solution is very much unreadable to anyone without advanced PowerShell knowledge and thus should not be propagated.

roxton Over a year ago

Looks like in all cases the first ? { $_ } is redundant.

Michael Sorens Over a year ago

@roxton First thank you for noticing that PowerShell has evolved so that the first null/empty filter is no longer needed!! While I appreciate your enthusiasm to also suggest an edit, I rejected it because it lost some context -- someone reading the original post that still showed the filter would be scratching their head a bit as to how he got from here to there. That's why I think your clear, concise comment just above (that it is redundant) is better. Thanks again!

mjolinor · Accepted Answer · 2012-03-07 00:31:01Z

7

You could do something like this:

($parts | foreach {$_.trim('/'))} -join '/'

edited Mar 7, 2012 at 0:31

answered Mar 6, 2012 at 23:40

mjolinor

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5 Comments

Serge van den Oever Over a year ago

I could not edit, but perfect answer. Must be: ($parts | foreach {$_.trim('/')}) -join '/'

mjolinor Over a year ago

Thanks. I missed that brace.

Serge van den Oever Over a year ago

But still not exactly: ('http:/fdfdfddf','','aa/bb' | ForEach-Object {$_.trim('/')}) -join '/' becomes http:/fdfdfddf//aa/bb, note the extra '/'

Serge van den Oever Over a year ago

What does GIGO mean? :-) Ahhh... Garbage in, Garbage out... but that is exactly my problem:-) I have multiple parts comming from an xml configuration file.

mjolinor Over a year ago

I can understand having multiple parts. None of your sample data indicate they were going to be as malformed as that mess.

Andy Arismendi · Accepted Answer · 2012-03-07 03:25:18Z

7

Here's an example creating URLs using the UriBuilder class:

$builder = New-Object System.UriBuilder
$builder.Host = "www.myhost.com"
$builder.Path = ('folder', 'subfolder', 'page.aspx' -join '/')
$builder.Port = 8443
$builder.Scheme = 'https'
$builder.ToString()

Outputs:

https://www.myhost.com:8443/folder/subfolder/page.aspx

Update - here's a little function that should be able to combine your URL parts:

function Join-Parts {
    param ([string[]] $Parts, [string] $Seperator = '')
    $search = '(?<!:)' + [regex]::Escape($Seperator) + '+'  #Replace multiples except in front of a colon for URLs.
    $replace = $Seperator
    ($Parts | ? {$_ -and $_.Trim().Length}) -join $Seperator -replace $search, $replace
}

Join-Parts ('http://mysite','sub/subsub','/one/two/three') '/'
Join-Parts ('http://mysite',$null,'one/two/three') '/'
Join-Parts ('http://mysite','','/one/two/three') '/'
Join-Parts (1,2,'',3,4) ','

Outputs:

http://mysite/sub/subsub/one/two/three
http://mysite/one/two/three
http://mysite/one/two/three
1,2,3,4

edited Mar 7, 2012 at 3:25

answered Mar 6, 2012 at 23:38

Andy Arismendi

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4 Comments

Serge van den Oever Over a year ago

Didn't know about this class! Tried with System.Uri. Problem is still with Path for multiple parts. Need mjoliner his answer for that one! But thanks!

Andy Arismendi Over a year ago

@SergevandenOever Yea System.Uri is the immutable version. You can get the System.Uri object from the builder by accessing the Uri property $builder.Uri.

Andy Arismendi Over a year ago

@SergevandenOever I added a little function to my answer that should be able to combine your fragments.

Serge van den Oever Over a year ago

Hi Andy, thanks for the extra function. Looks a bit expensive though. The answer by @msorens looks much lighter, so I chose his answer. Thanks for all your great thinking on my problem!

Ohad Schneider · Accepted Answer · 2018-12-06 13:40:36Z

7

Drawing inspiration from the top answer at Path.Combine for URLs?

function Combine-UriParts ($base, $path)
{
    return [Uri]::new([Uri]::new($base), $path).ToString()
}

Should be easy enough to extend to multiple parts

answered Dec 6, 2018 at 13:40

Ohad Schneider

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Comments

Richard · Accepted Answer · 2012-03-08 18:09:57Z

2

Powershell has a -join operator. for help type help about_join

edited Mar 8, 2012 at 18:09

Richard

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answered Mar 6, 2012 at 23:31

rerun

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