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Verilog-Perl - Overview of Verilog language packages for Perl


The Verilog-Perl distribution provides Perl parsing and utilities for the Verilog Language. This file provides an overview of the distribution.

Verilog-Perl is currently a mature tool. Bugs are fixed and IEEE language capabilities updated as needed, but the basic features and API are not expected to change.

For general information see

For specific details on each component, see that component's manpage.

You may also want to try the AUTO features present in Verilog-Mode.


The following scripts are installed by Verilog-Perl:


Vhier reads the Verilog files passed on the command line and outputs a tree of all of the filenames, modules, and cells referenced by that file.


Vpassert will read the specified Verilog files and preprocess special PLI assertions.


Vppreproc (Verilog-Perl Pre Processor) reads the Verilog files passed on the command line and outputs preprocessed output.


Vrename will allow a signal to be changed across all levels of the design hierarchy, or to create a cross reference of signal names.



Verilog::Getopt provides standardized handling of options similar to Verilog/VCS and cc/GCC.


Verilog::Language provides general utilities for using the Verilog Language, such as parsing numbers or determining what keywords exist.


Verilog::Netlist reads and holds interconnect information about a whole design database.


A Verilog::Netlist::Cell object is created by Verilog::Netlist for every instantiation in the current module.


A Verilog::Netlist::ContAssign object is created by Verilog::Netlist for every continuous assignment in the current module.


Verilog::Netlist::File allows Verilog::Netlist objects to be read and written in Verilog format.


A Verilog::Netlist::Module object is created by Verilog::Netlist for every module in the design.


A Verilog::Netlist::Net object is created by Verilog::Netlist::Module for every signal and input/output declaration in the current module.


A Verilog::Netlist::Pin object is created by Verilog::Netlist::Cell for for each pin connection on a cell.


A Verilog::Netlist::Port object is created by Verilog::Netlist::Module for every port connection in the module.


The Verilog::Netlist::Subclass is used as a base class for all Verilog::Netlist::* structures.


Verilog::Parser will tokenize a Verilog file and invoke various callback methods.


Verilog::Preproc reads Verilog files, and preprocesses them according to the Verilog specification. Programs can be easily converted from reading a IO::File into reading preprocessed output from Verilog::Preproc.


Verilog::SigParser builds upon the Verilog::Parser package to provide callbacks for when a signal is declared, a module instantiated, or a module defined.


If you are starting a new application which needs to parse the Verilog language you have several tools available to you. Which you pick depends on how low level and complete the information you need is.


The low level VParse* source files may be of use when you need a starting point for your own a full C++ SystemVerilog grammar parser, using Bison and Flex. It understands most of the SystemVerilog 2017 grammar (1800-2017 Appendix A).


Verilog::Preproc is useful when you need only post-preprocessed text output, or a list of defines, includes, etc. It can preprocess a file, or be used to provide the Verilog macro language on top of synthesis scripts. It understands and implements all preprocessor features of SystemVerilog 2017.


Verilog::Parser is useful when you need to tokenize or write source filters (where you need everything including whitespace). It can take raw files, or preprocessed input, and generates callbacks. It understands all SystemVerilog 2017 keywords.

Abstract Syntax Tree

Verilog::Parser knows enough to make a complete Abstract Syntax Tree (AST) of Verilog syntax. This represents all major constructs such as a "module" as a data structure, but does not interconnect the AST nodes as would be needed to follow signals. Not all keywords have been implemented; many are parsed but otherwise ignored. A complete Ast tree would allow any arbitrary transformation of Verilog syntax (everything is known excluding whitespace). For these applications consider Verilator's XML output (below).


Verilog::SigParser is useful when you need a list of modules, signals, ports, functions, etc. It requires a preprocessed file (from Verilog::Preproc), and can parse all SystemVerilog 2017 files, but only provides callbacks on certain interesting things. The SigParser operates only on a file at a time; it does not interconnect signals nor perform any elaboration (resolution of parameters).


Verilog::Netlist is useful for when you need the hierarchy, and a list of signals per module, pins per cell, etc. It builds upon the output of Verilog::SigParser, so requires preprocessed files (from Verilog::Preproc). It parses all SystemVerilog 2017 files, but not all SystemVerilog constructs are loaded into objects. Verilog::Netlist interconnects modules with instantiations but does not perform any elaboration (resolution of parameters).


Using the VPI is the best way to access the behavior of the design. It is not part of this package as it requires a compliant simulator and C++ code to call the VPI, and understands as much of the language as the simulator supports. This allows writing lint checks and full knowledge of all parts of the code. The VPI can operate ONLY on an elaborated design (where all parameters are resolved). Walking a VPI tree general requires a good deal of work compared to simple scripting (though little work compared to writing a parser from scratch).


The Verilator program also contains a very similar front end as Verilog-Perl and can create XML output showing the abstract syntax tree. Verilator also understands how to elaborate and connect complex pins and types, but supports a subset of SystemVerilog.

Verilog-Mode for Emacs

Although not a parser, a common requested use of Verilog-Perl is to automatically make shell modules and interconnect modules. Verilog-Mode is a project with a better solution to this problem, as it results in completely portable code; the program (Verilog-Mode) isn't needed for others to update the design. It's also in very common usage, including by many IP providers.


The SystemVerilog Language Services (slang) project provides various components for lexing, parsing, type checking, and elaborating SystemVerilog code. It's fast and supports UVM.


The Surelog project is a SystemVerilog 2017 Pre-processor, Parser, Elaborator, and UHDM Compiler. It handles UVM and provides an IEEE Design/TB C/C++ VPI and Python AST API.


The Sv-parser project is a SystemVerilog parser library fully compliant with IEEE 1800-2017. that returns a concrete syntax tree.


The Tree-Sitter-Verilog project is a verilog grammar for the JavaScript tree-sitter parser.


The Verible project parses IEEE 1800-2017, with the ability to parse un-preprocessed source files.


Skip this section if Verilog-Perl has already been installed.

Verilog-Perl should run on any system with Perl, G++, Flex, and Bison. It is known to work on most Linux distributions, plus Cygwin.

You may install using either CPAN, or the sources. If you plan to do any development on Verilog-Perl, use the sources.

CPAN Installation

Option 1: Easiest installation is using the "CPAN" command line that comes with Perl. After configuring CPAN the first time, simply

cpan install Verilog::Language
# And see the documentation
man Verilog-Perl
# Or, sometimes the capitalization is changed
man verilog-perl

Read the rest of this file for details on the programs provided.

Manual Installation from Repository

Option 2: Build any version using the source development repository with:

git clone  # Only first time
cd Verilog-Perl
git pull        # Make sure we're up-to-date
git tag         # See what versions exist (recent GITs only)
#git checkout master      # Use development branch (e.g. recent bug fix)
#git checkout stable      # Use most recent release
#git checkout v{version}  # Switch to specified release version

perl Makefile.PL
# Ignore warning about README, this file will be generated
make test
make install

Read the rest of this file for details on the programs provided.


Why do I get "unexpected `do'" or "unexpected `bit'" errors?

Do, bit, ref, return, and other words are now SystemVerilog keywords. You should change your code to not use them to insure it works with newer tools. Alternatively, surround them by the Verilog 2005/SystemVerilog begin_keywords pragma to indicate Verilog 2001 code.

`begin_keywords "1364-2001"
   integer bit; initial bit = 1;

Alternatively use the --language (for vhier) or Verilog::Language::language_standard call to specify "1364-2001", or for really old code, "1364-1995".

But, again, you really should fix the Verilog code.

With Verilog::Netlist how do I resolve signal widths that include parameters down to constants?

Unfortunately parameter resolution is part of elaboration. Verilog-Perl doesn't do elaboration as it requires a good fraction of a complete simulator implementation. Many applications can work around this limitation, if yours still requires elaboration you're stuck with using Verilator or the VPI, see the sections above.


Verilog-Perl is part of the free Verilog EDA software tool suite. The latest version is available from CPAN and from

Copyright 2000-2022 by Wilson Snyder. This package is free software; you can redistribute it and/or modify it under the terms of either the GNU Lesser General Public License Version 3 or the Perl Artistic License Version 2.0.

This code is provided with no warranty of any kind, and is used entirely at your own risk.


Wilson Snyder <>


vhier, vpassert, vppreproc, vrename

Verilog::EditFiles, Verilog::Getopt, Verilog::Language Verilog::Netlist, Verilog::Parser, Verilog::Preproc, Verilog::SigParser

Verilog::Netlist::Cell, Verilog::Netlist::ContAssign, Verilog::Netlist::File, Verilog::Netlist::Interface, Verilog::Netlist::ModPort, Verilog::Netlist::Module, Verilog::Netlist::Net, Verilog::Netlist::Pin, Verilog::Netlist::Port, Verilog::Netlist::Subclass,

And the package for Emacs.