TeamCityGetAssemblyInfoVersion.ps1

$folder = 'D:\Development\Repos\MyWebsite\My Project\'

$paths = gci -Recurse -Include "AssemblyInfo.vb", "AssemblyInfo.cs" -Path $folder

foreach($path in $paths) {
    # We need to filter out some invalid characters and possibly truncate the result and then we're good to go.  
    $info = (Get-Content $path) 

    $matches = ([regex]'AssemblyVersion\(\"([^\"]+)\"\)').Matches($info)

    foreach ($match in $matches) {
    
        if ($match.Success) {
            #incase the build number contains 1.0.*
            $newBuildNumber = $match.Groups[1].Value

            [version]$version = $null

            if ([Version]::TryParse($newBuildNumber, [ref]$version) -eq $true) {
                Write-Host "##teamcity[buildNumber '$($version.Major).$($version.Minor).$($version.Build).$($version.Revision)']" 
            }
        }
    }
}

TeamCitySetAssemblyInfoVersions.ps1

$buildNumber = '%build.number%'

$paths = gci -Include "AssemblyInfo.vb", "AssemblyInfo.cs" -Recurse -File 


foreach($path in $paths) {
    # We need to filter out some invalid characters and possibly truncate the result and then we're good to go.  
    $info = (Get-Content $path) 

    $info = ([regex]'AssemblyVersion\(\"([^\"]+)\"\)').Replace($info, "AssemblyVersion(""$buildNumber"")")
    $info = ([regex]'AssemblyFileVersion\(\"([^\"]+)\"\)').Replace($info, "AssemblyFileVersion(""$buildNumber"")")
    
    Set-Content -Path $path -Value $info
}