added <require 'httparty'> , created "setup.sh" which will make a ruby environment , fixed script error with invalid post names

blogspot_to_jekyll.rb

#!/usr/bin/env ruby
#
# Convert blogger (blogspot) posts to jekyll posts
#
# Basic Usage
# -----------
#
#   ./blogger_to_jekyll.rb feed_url
#
#  where `feed_url` can have the following format:
#
#  http://{your_blog_name}.blogspot.com/feeds/posts/default
#
# Requirements
# ------------
# 
#  * feedzirra: https://github.com/pauldix/feedzirra
#
# Notes
# -----
#
#  * Make sure Blogger shows full output of article in feeds.
#  * Commenting on migrated articles will be set to false by default.
#
#  Changes 02-09-2016 by Monica Schwehr
#
#   * removed deprecated CONFIG call, rubygems is required anyway
#   * Feedzirra is now feedjira, so I have corrected this as well
#
#  Changes 05-07-2021 by Robbi Nespu
#
#   * update feedjira fetch_and_parse method
#
#  Changes 19-07-2021 by prabathbr
#
#   * added <require 'httparty'>
#   * created "setup.sh" which will make a ruby environment to run the script in Ubuntu 20.04 LTS
#   * fixed script error[Invalid argument @ rb_sysopen --- post name ---- (Errno::EINVAL)] when running on posts with invalid post names with ":" & "*"



require 'rubygems' 
require 'feedjira'
require 'date'
require 'optparse'
require 'httparty'

def parse_post_entries(feed, verbose)
  posts = []
  feed.entries.each do |post|
    obj = Hash.new
    created_datetime = post.updated
    creation_date = Date.parse(created_datetime.to_s)
    title = post.title
    file_name = creation_date.to_s + "-" + title.split(/  */).join("-").delete('\/') + ".html"
    file_name = file_name.gsub(":", "-").gsub("*", "-")
    content = post.content
    
    obj["file_name"] = file_name
    obj["title"] = title
    obj["creation_datetime"] = created_datetime
    obj["updated_datetime"] = post.updated
    obj["content"] = content
    obj["categories"] = post.categories.join(" ")
    posts.push(obj)
  end
  return posts
end

def write_posts(posts, verbose)
  Dir.mkdir("_posts") unless File.directory?("_posts")

  total = posts.length, i = 1
  posts.each do |post|
    file_name = "_posts/".concat(post["file_name"])
    header = %{---           
layout: post
title: #{post["title"]}
date: #{post["creation_datetime"]}
updated: #{post["updated_datetime"]}
comments: false
categories: #{post["categories"]}
---

}
    File.open(file_name, "w+") {|f|
      f.write(header)
      f.write(post["content"])
      f.close
    }
    
    if verbose
      puts "  [#{i}/#{total[0]}] Written post #{file_name}"
      i += 1
    end
  end
end

def main
  options = {}
  opt_parser = OptionParser.new do |opt|
    opt.banner = "Usage: ./blogger_to_jekyll.rb FEED_URL [OPTIONS]"
    opt.separator ""
    opt.separator "Options"
    
    opt.on("-v", "--verbose", "Print out all.") do
      options[:verbose] = true
    end
  end

  opt_parser.parse!
  
  if ARGV[0]
    feed_url = ARGV.first
  else
    puts opt_parser
    exit()
  end

  puts "Fetching feed #{feed_url}..."
  xml = HTTParty.get(feed_url).body
  feed = Feedjira.parse(xml)
  
  puts "Parsing feed..."
  posts = parse_post_entries(feed, options[:verbose])
  
  puts "Writing posts to _posts/..."
  write_posts(posts, options[:verbose])

  puts "Done!"
end

main()

run.sh

#!/bin/bash
#
# This is an example of how to run it, you need to put the size otherwise it will load just 25 posts and 
# have a max of 500 posts every time 
# http://too-clever-by-half.blogspot.kr/2011/12/blog-feed-500-post-limit-for-more-than.html
#
ruby blogspot_to_jekyll.rb http://<blog>.com/feeds/posts/default?max-results=200

setup.sh

#!/bin/bash
#
# These commands will make a ruby environment to run the script in Ubuntu 20.04 LTS
#
sudo apt install ruby-full
ruby --version
sudo gem install "feedjira"
sudo gem install httparty

This is great. Good job! 👍