Assemble script files can be produced by Xic, and contain a specification for complicated operations on layout files, such as merging several files into a single output file, while creating a new top-level cell to contain instances of the cells read from input. These files can be evaluated with the FileTool.
The command is of the form
filetool [-set variables] -eval script_file
The FileTool will read and execute the script, reading input and generating output as per the directives in the script file.
The script file format is described in 19.2.3.