Ruby by Example

#10 Showing Line Numbers (line_num.rb)

Another useful trick when dealing with text files is the ability to automatically add line numbers to them. Here’s a script that does just that.

The Code

  #!/usr/bin/env ruby
  # line_num.rb

❶ def get_lines(filename)
    return File.open(filename, 'r').readlines
  end

❷ def get_format(lines)
    return "%0#{lines.size.to_s.size}d"    sprintf Formats
  end

❸ def get_output(lines)
    format = get_format(lines)
❹   output = ''    The each_with_index and sprintf Methods
❺   lines.each_with_index do |line,i|
❻     output += "#{sprintf(format, i+1)}: #{line}"
    end
    return output
  end

  print get_output(get_lines(ARGV[0]))

How It Works

The get_lines method (❶) should look familiar at this point, since we’ve covered some very similar methods earlier in ...