Grep in Ruby

Here’s an attempt at building a grep-alternative in Ruby…

#!/usr/bin/env ruby

#
# Author: Katkam Nitin Reddy
# Email: <redknitin@gmail.com>
# Date: 2023-02-08
# Description: Replacement for grep with support for lookahead/lookbehind
#

require 'optparse'
require 'colorize'

def process(options)
  input = File.read options[:inputfile] unless options[:inputfile]=='-'
  input = ARGF.read if options[:inputfile]=='-'
  # input = STDIN.gets if options[:inputfile]=='-'  # This returns only 1 line, so we use ARGF.read instead

  input.each_line do |iter_line|
    if not (mat = iter_line.match(options[:pattern])).nil?

      if options[:output_match_group]==0
        before_text = iter_line[0..mat.begin(0)-1] unless mat.begin(0)==0
        match_text = mat[0]
        after_text = iter_line[mat.end(0)..]
        puts "#{before_text}#{match_text.red}#{after_text}"
      else
        puts mat.captures[options[:output_match_group]-1]
      end

      # p '--'
    end
  end
end

# Entry point for the application; parse args and call process()
def main
  # Default options
  options = {
    processing_type: :normal,
    output_match_group: 0
  }

  # Define the parser
  parser = OptionParser.new do |opts|
    opts.banner = 'Usage: rp.rb <pattern> <file>'
    opts.on('-e PATTERN', '--pattern=PATTERN', 'Regex Pattern') do |the_param|
      options[:pattern] = the_param
    end
    opts.on('-f FILENAME', '--file=FILENAME', 'Input file') do |the_param|
      options[:inputfile] = the_param
    end
    opts.on('-o CAP_GROUP_NUM', '--matchgroup=CAP_GROUP_NUM', 'Specify captured group number to output') do |the_param|
      options[:output_match_group] = the_param.to_i
    end
  end

  # Parse the ARGV
  remaining_args = parser.parse!

  # Take parameters not passed as arguments
  # Pop returns in reverse order, so we start with the right-most argument first

  # Take the input file if there is nothing being piped
  if STDIN.tty? and not options.has_key? :inputfile   # STDIN.tty? returns false if we have piped content
    options[:inputfile] = remaining_args.pop
  elsif not options.has_key? :inputfile and not options.has_key? :inputfile
      options[:inputfile] = '-'
  end

  # Take the pattern
  if not options.has_key? :pattern
    options[:pattern] = remaining_args.pop
  end

  process options
end

# Enables us to use this as a library of functions
main if __FILE__ == $0