mergeCompareCsv.ps1

<#
.SYNOPSIS
  Merges two CSV files with common attribute set

.EXAMPLE
  ./mergeCompareCsv.ps1 ./users1.csv ./users2.csv -outfile merged.csv -Delimiter ';'
#>

[CmdletBinding()]
Param (
    [parameter(Position = 0, Mandatory = $true)]
    [String]$file1,
    [parameter(Position = 1, Mandatory = $true)]
    [String]$file2,
    [parameter()]
    [String]$outfile,
    [parameter()]
    [char]$Delimiter = ',',
    [parameter()]
    [String]$htmlReportFile
)

$ErrorActionPreference = "Stop"

# func to create merged object, edit for your use case / file headers
function mergeObjs {
    [CmdletBinding()]
    param(
        $o1,
        $o2
    )

    $obj = [pscustomobject]@{
        id            = $null -ne $o1 ? $o1.id : $o2.id
        firstName     = $null -ne $o1.firstName ? $o1.firstName : $o2.firstName
        lastName      = $null -ne $o1.lastName ? $o1.lastName : $o2.lastName
        existsIn1     = $null -ne $o1 ? $true : $false 
        existsIn2     = $null -ne $o2 ? $true : $false
        birthday1     = $o1.birthday
        birthday2     = $o2.birthday 
        birthdayEqual = $o1.birthday -eq $o2.birthday
    }    
    return $obj
}

# Import CSV files
$csv1 = Import-Csv -Encoding 'utf8' -Delimiter $Delimiter -Path $file1
$csv2 = Import-Csv -Encoding 'utf8' -Delimiter $Delimiter -Path $file2

# create maps with id as index
$m1 = @{}
foreach ( $c1 in $csv1 ) {
    $m1[$c1.id] = $c1 
} 

$m2 = @{}
foreach ( $c2 in $csv2 ) {
    $m2[$c2.id] = $c2 
} 

# merge with m1 as master
$merged = @()
foreach ( $i in $m1.Values ) {
    $merged += mergeObjs -o1 $i -o2 $m2[$i.id]
}

# add missing entries from m2
foreach ( $i in $m2.Values ) {
    if ( $null -eq $m1[$i.id] ) {
        $merged += mergeObjs -o1 $null -o2 $i
    }
}

# write to CSV
if ( $outfile ) {
    $merged | Export-Csv -Delimiter $Delimiter -Path $outfile -Encoding 'utf8' -UseQuotes AsNeeded
}

# print to output
$merged | ft

# Generate Report with Module PSWriteHTML (Install with: Install-Module -Name PSWriteHTML -Scope CurrentUser -Force)
if ($htmlReportFile -and (Get-Module -ListAvailable -Name PSWriteHTML) ) {
    $table = { New-HTMLTable -DataTable $merged -HideFooter -PagingLength 100 -Html {
            New-TableCondition -Name 'birthdayEqual' -ComparisonType string -Operator eq -Value 'False' -Color Orange        }
    }
    New-HTML -HtmlData $table -FilePath $htmlReportFile -ShowHTML  -TitleText 'Merged'
}