How to Print All Instances in a Verilog Netlist with Perl

When working with Verilog netlists, you might find yourself needing to extract specific instances of modules or components from these files. This can often involve parsing the text to match particular patterns. In this article, we will explore how to use Perl to print all instances in a Verilog netlist by leveraging regex patterns. We'll also demonstrate how to achieve similar results using egrep for those who prefer command-line tools. Understanding the Verilog Instance Format Verilog is a hardware description language used to model electronic systems. Instances in a Verilog netlist are typically structured in the following format: name name_inst( camera cam_inst( Here, name can be anything and name_inst always ends with an opening parenthesis (. This pattern allows us to identify each instance. Using Perl to Match Instances To extract instances with Perl, we can use regular expressions to search for the specified format. Below are the steps to accomplish this: Step 1: Basic Perl Script We'll start by creating a simple Perl script that reads through a Verilog netlist file and matches the required instance names using regex. #!/usr/bin/perl use strict; use warnings; # Open the Verilog netlist file my $filename = 'netlist.v'; open my $fh, '

May 13, 2025 - 06:48

How to Print All Instances in a Verilog Netlist with Perl

When working with Verilog netlists, you might find yourself needing to extract specific instances of modules or components from these files. This can often involve parsing the text to match particular patterns. In this article, we will explore how to use Perl to print all instances in a Verilog netlist by leveraging regex patterns. We'll also demonstrate how to achieve similar results using egrep for those who prefer command-line tools.

Understanding the Verilog Instance Format

Verilog is a hardware description language used to model electronic systems. Instances in a Verilog netlist are typically structured in the following format:

name name_inst(
camera cam_inst(

Here, name can be anything and name_inst always ends with an opening parenthesis (. This pattern allows us to identify each instance.

Using Perl to Match Instances

To extract instances with Perl, we can use regular expressions to search for the specified format. Below are the steps to accomplish this:

Step 1: Basic Perl Script

We'll start by creating a simple Perl script that reads through a Verilog netlist file and matches the required instance names using regex.

#!/usr/bin/perl
use strict;
use warnings;

# Open the Verilog netlist file
my $filename = 'netlist.v';
open my $fh, '<', $filename or die "Could not open file '$filename' $!";

while (my $line = <$fh>) {
    if ($line =~ /\b\w+\s+(\w+_inst)\s*\(/) {
        print "Instance Found: $1\n";
    }
}

close $fh;

Step 2: Explanation of the Script

The script begins by opening a Verilog netlist file named netlist.v.
It reads the file line by line, checking each line against the regex pattern.
The regex pattern \b\w+\s+(\w+_inst)\s*\( looks for:
- \b\w+ : a word boundary followed by one or more word characters to match name.
- \s+ : one or more whitespace characters.
- (\w+_inst) : capturing the instance name that follows and ends with _inst.
- \s*\( : optional whitespace followed by an opening parenthesis, ensuring we are identifying the instance accurately.
When a match is found, it prints the instance name using $1, which captures the matched instance.

Step 3: Running the Script

To run the script, save it as extract_instances.pl, provide execution permissions, and execute it:

chmod +x extract_instances.pl
./extract_instances.pl

Using egrep for Quick Matching

If you're looking for a quick command-line solution, egrep is a powerful option. Below is an example command you can run directly in your terminal:

egrep -o '\b\w+\s+\w+_inst\s*\(' netlist.v

In this command:
- -o ensures that only the matched parts are printed.
- The regex pattern matches the same format as discussed earlier.

Conclusion

In summary, extracting instances from a Verilog netlist can be efficiently handled using Perl or egrep. The Perl script provides a robust way to handle file input and regex matching, while egrep offers a quick command-line solution. Depending on your workflow and preferences, either approach can be utilized to achieve the desired results. Use these methods to streamline your Verilog netlist parsing tasks!