read - load HDL designs

    read {-vlog95|-vlog2k|-sv2005|-sv2009|-sv2012|-sv|-formal} <verilog-file>..

Load the specified Verilog/SystemVerilog files. (Full SystemVerilog support
is only available via Verific.)

Additional -D<macro>[=<value>] options may be added after the option indicating
the language version (and before file names) to set additional verilog defines.

    read {-vhdl87|-vhdl93|-vhdl2k|-vhdl2008|-vhdl} <vhdl-file>..

Load the specified VHDL files. (Requires Verific.)

    read -define <macro>[=<value>]..

Set global Verilog/SystemVerilog defines.

    read -undef <macro>..

Unset global Verilog/SystemVerilog defines.

    read -incdir <directory>

Add directory to global Verilog/SystemVerilog include directories.

    read -verific
    read -noverific

Subsequent calls to 'read' will either use or not use Verific. Calling 'read'
with -verific will result in an error on Yosys binaries that are built without
Verific support. The default is to use Verific if it is available.