Class: IMW::Parsers::RegexpParser

Inherits:
LineParser show all
Defined in:
lib/imw/parsers/regexp_parser.rb

Overview

A RegexpParser is a line-oriented parser which uses a regular expression to extract data from a line into either a hash or an object obeying hash semantics.

As an example, a flat file with one record per line in the following format (this is a simplified version of common webserver log formats)

151.199.53.145 14-Oct-2007:13:34:34-0500 GET /phpmyadmin/main.php HTTP/1.0
81.227.179.120 14-Oct-2007:13:34:34-0500 GET /phpmyadmin/libraries/select_lang.lib.php HTTP/1.0
81.3.107.173 14-Oct-2007:13:54:26-0500 GET / HTTP/1.1
...

could be parsed as follows

file   = File.new '/path/to/file.log'
parser = IMW::Parsers::RegexpParser.new :by_regexp   => %r{^([\d\.]+) (\d{2}-\w{3}-\d{4}:\d{2}:\d{2}:\d{2}-\d{4}) (\w+) ([^\s]+) HTTP/([\d.]{3})$},
                                        :into_fields => [:ip, :timestamp, :verb, :url, :version]
parser.parse file #=> [{:ip => '151.199.53.145', :timestamp => '14-Oct-2007:13:34:34-0500', :verb => 'GET', :url => '/phpmyadmin/main.php', :version => "1.0"}, ... ]

Consecutive captures from the regular expression will be pushed into a hash with keys given by the into_fields property of this parser.

If the parser is instantiated with the :of keyword then the parsed hash from each line is used to instantiate a new object of the corresponding class:

require 'ostruct'

PageView = Class.new(OpenStruct)

parser = IMW::Parsers::RegexpParser.new :by_regexp   => %r{^([\d\.]+) (\d{2}-\w{3}-\d{4}:\d{2}:\d{2}:\d{2}-\d{4}) (\w+) ([^\s]+) HTTP/([\d.]{3})$},
                                        :into_fields => [:ip, :timestamp, :verb, :url, :version],
                                        :of          => PageView

parser.parse! file #=> [#<PageView ip="151.199.53.145", timestamp="14-Oct-2007:13:34:34-0500", verb="GET", url="/phpmyadmin/main.php", version="1.0">, ... ]

The option :strictly can also be set to force the parser to raise an error if it finds a line which doesn’t match its regexp.

Instance Attribute Summary collapse

Attributes inherited from LineParser

#klass, #skip_first

Instance Method Summary collapse

Methods inherited from LineParser

#parse!

Constructor Details

#initialize(options = {}) ⇒ RegexpParser

Returns a new instance of RegexpParser.



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# File 'lib/imw/parsers/regexp_parser.rb', line 50

def initialize options={}
  @regexp = options[:regexp] || options[:by_regexp]
  @fields = options[:fields] || options[:into_fields]
  @strict = options[:strict] || options[:strictly]
  super options
end

Instance Attribute Details

#fields ⇒ Object

Returns the value of attribute fields.



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# File 'lib/imw/parsers/regexp_parser.rb', line 48

def fields
  @fields
end

#regexp ⇒ Object

Returns the value of attribute regexp.



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# File 'lib/imw/parsers/regexp_parser.rb', line 48

def regexp
  @regexp
end

#strict ⇒ Object

Returns the value of attribute strict.



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# File 'lib/imw/parsers/regexp_parser.rb', line 48

def strict
  @strict
end

Instance Method Details

#parse_line(line) ⇒ Object 



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# File 'lib/imw/parsers/regexp_parser.rb', line 57

def parse_line line
  match_data = regexp.match(line.chomp)
  returning({}) do |hsh|
    if match_data
      match_data.captures.each_with_index do |capture, index|
        hsh[fields[index]] = capture
      end
    else
      raise IMW::ParseError.new("Could not parse the following line:\n\n#{line}\n\nusing regexp\n\n#{regexp.to_s}") if strict
    end
  end
end