You can use the $(SharePointSiteUrl)
variable in the post-build event. $(SharePointSiteUrl)
is an extra variable that is available for SharePoint projects.
$(SharePointSiteUrl) is the URL you’ve selected in the properties of
the SharePoint project.
$(TargetDir)$(TargetName).wsp is the name of the solution package
file.
For flexibility, instead of using hard-coded strings in the
Pre-deployment Command Line and Post-deployment Command Line boxes on
the SharePoint Properties page, you can use the SharePoint properties
as arguments. For example, instead of specifying a specific URL string
for the SharePoint site, you can instead use $(SharePointSiteUrl).
Here is the complete list: http://msdn.microsoft.com/en-us/library/ee696754%28VS.100%29.aspx