Here is an example TCL script on how to automate adding of files, based on file type, to a Radiant project via scripting flow:
#set the directory to a variable where you want to get the files.
set dir /home/jmangubat/
#use glob command to filter the files based on the file type. In this example, *.vhd file type is filtered.
set file_list [glob -directory $dir *.vhd]
#use foreach to list the filtered files and add them to the project one by one.
foreach file $file_list
{
prj_add_source -impl impl1 $file
}