Installing the source from Git is done as follows:

git clone git://github.com/tenable/nasl.git

Installing the package from RubyGems is done as follows:

gem install nasl

To avoid conflicting with the NASL interpreter, the NASL gem's binary is installed as nasl-parse. As an application, it has very few actions that it can perform.

• Benchmark: This benchmarks the time taken to parse the input path(s) over a number of iterations. The number of iterations can be adjusted by the -i switch.

    % nasl-parse -i 10 benchmark /opt/nessus/lib/nessus/plugins/ssl_certificate_chain.nasl
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
    Rehearsal --------------------------------------------
    Tokenize   1.687500   0.000000   1.687500 (  1.688397)
    Parse      1.835938   0.015625   1.851562 (  1.857094)
    ----------------------------------- total: 3.539062sec
    
                   user     system      total        real
    Tokenize   1.304688   0.015625   1.320312 (  1.319951)
    Parse      1.046875   0.000000   1.046875 (  1.046957)
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
  

• Parse: This parses the input path(s) and indicates whether the parse was successful.

    % nasl-parse parse /opt/nessus/lib/nessus/plugins/ssl_certificate_chain.nasl
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
    Successfully parsed the contents of the file.
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
  

• Test: This runs unit tests distributed with the application. Specific unit tests can be specified on the command line, otherwise all tests will be run.

    % nasl-parse test
    Run options:
    
    # Running tests:
    
    .............................................................................
    
    Finished tests in 11.773983s, 6.5398 tests/s, 33493.8487 assertions/s.
    
    77 tests, 394356 assertions, 0 failures, 0 errors, 0 skips
  

• Tokenize: This tokenizes the input path(s) and prints the token/byte-range pairs to stdout.

    % nasl-parse tokenize /opt/nessus/lib/nessus/plugins/ssl_certificate_chain.nasl
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
    [COMMENT,              0...1076]
    [IF,                1076...1079]
    [LPAREN,            1079...1080]
    [IDENT,             1080...1091]
    [CMP_LT,            1091...1093]
    ...
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
  

• XML: This parses the input path(s), and then prints an XML representation of the parse tree to stdout.

    % nasl-parse xml /opt/nessus/lib/nessus/plugins/ssl_certificate_chain.nasl
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
    <tree>
      <if>
        <expression>
          <op>&lt;</op>
          <lvalue>
    ...
    -------------------------[ ssl_certificate_chain.nasl ]-------------------------
  

The primary users of this gem are Pedant and Nasldoc. Other uses are encouraged, of course! The Parser class is the most useful part, obviously, and can be used as follows:

require 'nasl'

tree = Nasl::Parser.new.parse(file_contents, path_to_file)

That's all there is to it. If there are any errors, it'll throw an instance of ParseException that will include as much context about the error as possible.

This project uses Bundler.

If you have a brand-new Debian machine, do this as root:

apt-get install ruby-dev rubygems git
gem install bundler

As your regular user:

git clone https://github.com/tenable/nasl
cd nasl
bundle install --path vendor/bundle
bundle exec rake grammars
bundle exec rake test

All the tests should pass!

To run the nasl-parse command line, do bundle exec ./bin/nasl-parse, which should give a help message.