# Comparing CSV files

**URL:** <https://forums.powershell.org/t/comparing-csv-files/21251>\
**Category:** PowerShell Help\
**Created:** [December 30, 2022, 10:44am UTC](https://forums.powershell.org/t/comparing-csv-files/21251 "2022-12-30T10:44:57Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![dpj](https://avatars.discourse-cdn.com/v4/letter/d/bbe5ce/32.png) [@dpj](https://forums.powershell.org/u/dpj)\
**Post date:** [December 30, 2022, 10:44am UTC](https://forums.powershell.org/t/comparing-csv-files/21251/1 "2022-12-30T10:44:58Z")

</div>

Hello there, Next question.

I have 2 scripts, 1 is working, one is not. But I don’t know why one is not working. It looks ok for me.  
first i will use the working one:

I have a CSV file on my computer. The first few lines are these:  
A;B  
00-00-0C;Cisco Systems, Inc  
00-00-0D;FIBRONICS LTD.  
00-00-0E;FUJITSU LIMITED  
00-00-1B;Novell, Inc.

I import this file like this:

```auto
$map = @{}
Import-Csv C:\tmp\mac-vendors-export.csv -Delimiter ';' | ForEach-Object {
    $map[$_.A] = $_.B
}

```

What i want allready have achieved is to scan my network. retrieve mac addresses, and then compare it with this CSV, and show the corresponding column B result.

```auto
VendorList = $vendorMac | ForEach-Object {
    [pscustomobject]@{
        MAC = $_
        Vendor = $map[$_]
    }

```

BUT, i have to go a step further. because in real live i don’t have this file on my computer. So i have to download it, and compare it after this. But the downloaded file is a litte different formatted.

so my code look like this:  
`invoke-webrequest -uri "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0" -outfile $Env:temp\mac-vendor.csv`

the file look like this:  
Mac Prefix,Vendor Name,Private,Block Type,Last Update  
00:00:0C,“Cisco Systems, Inc”,false,MA-L,2015/11/17  
00:00:0D,FIBRONICS LTD.,false,MA-L,2015/11/17  
00:00:0E,FUJITSU LIMITED,false,MA-L,2018/10/13  
00:00:1B,“Novell, Inc.”,false,MA-L,2016/04/27  
00:00:23,ABB INDUSTRIAL SYSTEMS AB,false,MA-L,2015/11/17

```auto

Import-CSV $ENV:Temp\mac-vendor.csv -Delimiter ',' -Header 'MAC','Vendor' | Select-object 'MAC','Vendor' -Skip 1 | ForEach-Object {
    $map[$_.MAC] = $_.Vendor
}   
    

$VendorList = $vendormac | ForEach-Object {
    [pscustomobject]@{
        MAC = $_
        Vendor = $map[$_]
    }
}

```

I see when i show the $vendorlist variable i receive no vendors  
PS C:\WINDOWS\system32\> $VendorList

MAC Vendor

* * *

74-83-c2  
d2-51-e5  
60-ab-14  
18-e8-29  
bc-cf-4f  
2e-d9-2c  
00-11-32  
c0-3f-d5  
18-e8-29

And in the working script it’s filled with information

so it must be somewhere in this part i think

```auto
$vendormac | ForEach-Object {
    [pscustomobject]@{
        MAC = $_
        Vendor = $map[$_]
    }
}

```

I hope my question is clear enough

---

<div class="post-metadata">

**Author:** ![Olaf](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.powershell.org/olaf/32/992_2.png) [@Olaf](https://forums.powershell.org/u/Olaf)\
**Post date:** [December 30, 2022, 11:51am UTC](https://forums.powershell.org/t/comparing-csv-files/21251/2 "2022-12-30T11:51:11Z")

</div>

Before we proceed … please keep in mind … we cannot see your screen and we cannot read your mind … 😉

Please go back, edit your question again and fix the formatting of your code, console output and sample data.  
To do so use the _preformatted text_ button ( **\</\>** ). Simply place your cursor on an empty line, click the button and paste your code.

Thanks in advance

[How to format code in PowerShell.org](https://us1.discourse-cdn.com/flex019/uploads/powershell/original/2X/b/bee50c628238f2c076c0504efb6b15f2fb11f002.gif) \<---- Click 👆🏽 😉

---

<div class="post-metadata">

**Author:** ![dpj](https://avatars.discourse-cdn.com/v4/letter/d/bbe5ce/32.png) [@dpj](https://forums.powershell.org/u/dpj)\
**Post date:** [December 30, 2022, 11:58am UTC](https://forums.powershell.org/t/comparing-csv-files/21251/3 "2022-12-30T11:58:35Z")

</div>

ah that looks better!

---

<div class="post-metadata">

**Author:** ![Olaf](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.powershell.org/olaf/32/992_2.png) [@Olaf](https://forums.powershell.org/u/Olaf)\
**Post date:** [December 30, 2022, 12:31pm UTC](https://forums.powershell.org/t/comparing-csv-files/21251/4 "2022-12-30T12:31:23Z")

</div>

> [@dpj](#):
>
> ah that looks better!

Hmmm … no comment on that. 😏

So you want to add the vendor information to the list of MAC addresses you have from the scan of your network, right?

> [@dpj](#):
>
> I see when i show the $vendorlist variable i receive no vendors

I’d use another approach. Instead of preparing a lookup hashtable I’d use the CSV data right away.

Could you share some sample input data from your network scan and some according vendor data?

And BTW: the format of your MAC addresses seems to be different. Once you have colons and once dashs. `74-83-c2` vs `00:00:0E`!! 👆🏽 😉

---

<div class="post-metadata">

**Author:** ![krzydoug](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.powershell.org/krzydoug/32/1008_2.png) [@krzydoug](https://forums.powershell.org/u/krzydoug)\
**Post date:** [December 30, 2022, 8:02pm UTC](https://forums.powershell.org/t/comparing-csv-files/21251/5 "2022-12-30T20:02:22Z")

</div>

First thing, you don’t specify headers when the csv already has headers, that’s going to screw up the data. Second thing, your vendorlist shows dashes in the MAC addresses, this will not match the link you’re trying to download as they are colons.

First example, simply convert to csv as it is

```auto
Invoke-RestMethod -uri "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0" -UseBasicParsing | ConvertFrom-Csv

```

However when you look at this, you’ll see the properties are not the friendliest (they include spaces.) You can fix these with some calculated properties.

```auto
$url = "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0"

Invoke-RestMethod -uri $url -UseBasicParsing |
    ConvertFrom-Csv | Select-Object @{n='MAC';e='Mac Prefix'},
                                    @{n='Vendor';e='Vendor Name'},
                                    Private,
                                    @{n='BlockType';e='Block Type'},
                                    @{n='Updated';e='Last Update'}

```

Or with a PSCustomObject

```auto
$url = "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0"

Invoke-RestMethod -uri $url -UseBasicParsing |
    ConvertFrom-Csv | ForEach-Object {
        [PSCustomObject]@{
            MAC = $_.'Mac Prefix'
            Vendor = $_.'Vendor Name'
            Private = $_.Private
            BlockType = $_.'Block Type'
            Updated = $_.'Last Update'
        }
    }

```

From there you can just select the two columns you want. However if you wanted to shortcut to this end, you could simply do

```auto
$url = "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0"

$output = Invoke-RestMethod -uri $url -UseBasicParsing

$output -split '\r?\n' | Select-Object -Skip 1 | ConvertFrom-Csv -Header Mac,Vendor,a,b,c | Select-Object Mac, Vendor

```

Now as we mentioned, the different MAC formats should be dealt with. If you want to change the colons to dashes, add to your calculated properties or PSCustomObject

```auto
$_.'Mac Prefix' -replace ':','-'

```

Like so

```auto
$url = "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0"

Invoke-RestMethod -uri $url -UseBasicParsing |
    ConvertFrom-Csv | Select-Object @{n='MAC';e={$_.'Mac Prefix' -replace ':','-'}},
                                    @{n='Vendor';e='Vendor Name'},
                                    Private,
                                    @{n='BlockType';e='Block Type'},
                                    @{n='Updated';e='Last Update'}

```

Or

```auto
$url = "https://maclookup.app/downloads/csv-database/get-db?t=22-12-28&h=a6f90f116bc4364ad17817cff62fd160fbff73c0"

Invoke-RestMethod -uri $url -UseBasicParsing |
    ConvertFrom-Csv | ForEach-Object {
        [PSCustomObject]@{
            MAC = $_.'Mac Prefix' -replace ':','-'
            Vendor = $_.'Vendor Name'
            Private = $_.Private
            BlockType = $_.'Block Type'
            Updated = $_.'Last Update'
        }
    }

```

And finally, you don’t have to create a hash map. You can access the properties of the data right from the objects created by the csv cmdlet. There are reasons why one would need or choose to do a hash table, just wanted to make sure you knew you didn’t have to.

---

<div class="post-metadata">

**Author:** ![dotnVo](https://avatars.discourse-cdn.com/v4/letter/d/4af34b/32.png) [@dotnVo](https://forums.powershell.org/u/dotnVo)\
**Post date:** [May 16, 2024, 8:16pm UTC](https://forums.powershell.org/t/comparing-csv-files/21251/6 "2024-05-16T20:16:12Z")

</div>