Converting Multiple SharePoint 2010 Projects to SharePoint 2013

Converting/migrating SharePoint 2010 projects to SharePoint 2013 involves changing TargetOfficeVersion to be 15.0, and changing TargetFrameworkVersion to be v4.0 or v4.5 in the Visual Studio csproj file.

When you have multiple SharePoint 2010 projects in your solution, it will not be an easy task!

The following PowerShell script is my trial to simplify converting multiple projects, hope it will help.
Just change the value of the $path variable to be your solution path (the folder containing your SharePoint projects).

# Path containing SharePoint 2010 projects 
$path = "<Your Solution Folder Path>"

cd $path
$files = get-childitem -recurse -filter *.csproj

foreach ($file in $files)
{
    "Filename: {0}" -f $($file.Name)
    $proj = [xml](Get-Content $file.FullName)

    $ns = new-object Xml.XmlNamespaceManager $proj.NameTable
    $ns.AddNamespace("dns", 
    "http://schemas.microsoft.com/developer/msbuild/2003")
    $projectTypeGuids = $proj.SelectSingleNode
    ("//dns:Project/dns:PropertyGroup/dns:ProjectTypeGuids", $ns)
 
 # Check to see if the project type is SharePoint 
 if ($projectTypeGuids."#text" 
 -like "*BB1F664B-9266-4fd6-B973-E1E44974B511*")
 {
  $targetOfficeVersion = $proj.SelectSingleNode
  ("//dns:Project/dns:PropertyGroup/dns:TargetOfficeVersion", $ns)
  if($targetOfficeVersion -eq $null)
  {
   # Create TargetOfficeVersion element if not exist
   $targetOfficeVersion = $proj.CreateElement("TargetOfficeVersion")
   $targetOfficeVersion = $proj.SelectSingleNode
   ("//dns:Project/dns:PropertyGroup", $ns).AppendChild($targetOfficeVersion)
  }

  # Change target office version
  $targetOfficeVersion.InnerText = "15.0"

  # Change target framework version
  $targetFrameworkVersion = $proj.SelectSingleNode
  ("//dns:Project/dns:PropertyGroup/dns:TargetFrameworkVersion", $ns)
  $targetFrameworkVersion.InnerText = "v4.5"

      # Remove empty namespaces
  $proj = [xml] $proj.OuterXml.Replace(" xmlns=`"`"", "")
  $proj.Save($file.FullName)
 }
}