Table of contents

• What
• Why
• The Tools
• Show me the code

What

This is post is going to be referring to this custom promotion-code generating CLI’s code, and about useful tools that helped in building it. All the tools mentioned are native to Ruby (no external gems were used)

The data generated is going to be stored in a JSON object, and has the following format:

"<FirstName LastName>": {
  "code": "String: Generated code",
  "activated": "Boolean"
}

You may think “Wait a minute there, that’s not a scalable solution, isn’t it?”

Well, yes, ideally, the promotion codes should be directly connected to your database. But if you want a quick solution, this should be fine

Also, keep in mind that this is not storing your main data. It’s just storing the promotion codes and checking whether they’re activated or not. It has a constant (O(1)) lookup and write time-complexity, and can hold an awful lot of data. Approximately, a JSON file can hold about 18 quintillion characters. For context: “Harry Potter and the Deathly Hallows” has about 1 million characters. So, in total, a JSON file would hold about 13 trillion copies of that book. That’s a lot!

Why

“Why should I bother with creating a custom promotion-code generator?”

As you may know, promotional codes are typically used in stores, offline and online, to drive traffic. Generally speaking, general promotion codes (ones not mapped to a specific person), don’t need to be unique. In fact, you want them to be generic to drive as much traffic to your store as possible. They should be easy to guess and could be safely made up by humans

Customized promotion codes, on the other hand, though intended to also drive traffic, have another sole purpose. The main purpose of them should be to get specific people onto your platform

Understanding that these codes are made for specific people, you want them to be harder to guess. That is because we don’t want some imposter claiming our invitees' rewards

Hope that makes sense. If not, feel free to drop a comment

The Tools

1. Kernel#puts

Prints string on single line (doesn’t allow other stuff to get printed on same line)

Example:

puts 'Hello'
puts 'world'

Output:

Hello
World

2. Kernel#gets and String#chomp

gets: Takes input from shell

chomp: Takes off newline character ("\n") off from end of string. This character gets generated when user hits the enter key

Put together because they are often used together. Just having Kernel#gets will leave you with a string with "\n" at the end of it

The following example uses both to avoid that

Example:

puts 'Please say something: '

answer = gets.chomp

puts answer

Output:

$ Please say something: Hello
Hello

Note: The project referred to in this post doesn’t use gets.chomp and uses Readline (#3) instead. That is since Readline provides autocompletion, history reference, and other useful functionalities. But gets.chomp could be useful for getting simple input in some instances. So it’s worth the mention

3. Readline::readline(<file name>, <refer to history bool>)

Takes input from shell. Takes off newline character ("\n") automatically

Second argument takes boolean to flag whether to remember history or not. If you set to true, it will remember previous answers from same file-run session

Example:

require 'readline'

answer = Readline.readline('Please say something: ', true)

puts answer

answer = Readline.readline('Please say something: ', true)

puts answer

Output:

$ Please say something: Hello
Hello
$ Please say something: [*click up-arrow*]
$ Please say something: Hello
Hello

4. Readline::completion_proc = <proc>

Adds autocompletion functionality based on given proc

Example:

require 'readline'

LIST = ['action', 'bear', 'computer']

comp = proc { |s| LIST.grep(/^#{Regexp.escape(s)}/) }

Readline.completion_proc = comp
Readline.readline('', true)

Output:

$ co[*click on tab*]
$ computer

5. String#downcase

Lower-cases a string

Useful for keeping data format consistent

Example:

puts 'HELLO WORLD'.downcase

Output:

hello world

6.String#strip

Takes off whitespace from beginning and end of string

Useful for keeping data format consistent

Example:

puts ' hi there '.strip

Output:

hi there

(I know it doesn’t show up there, but there should be no white spaces at the ends of the string)

7. IO.read(<file name>)

Reads file content and returns it as string

Example:

file_content = IO.read('data.json')

puts file_content

Output:

"{\"some key\": \"some value\"}"

8. JSON#parse(<json string>)

Converts JSON string to JSON object

Example:

require 'json'

puts JSON.parse("{\"some key\": \"some value\"}")

Output:

{"some key": "some value"}

9. JSON#dump(<json string>)

Converts JSON object to JSON string

Example:

require 'json'

puts JSON.dump({"some key": "some value"})

Output:

"{\"some key\": \"some value\"}"

10. File::Open(<file name>, ‘w’) {|file| <changes to file>}

Opens and writes data to file (writing automatically gets it saved)

Example:

require 'json'

file_name = 'data.json'
new_data = {"some new key": "some new value"}

File.open(file_name,'w'){ |file| JSON.dump(new_data, file) }
json = JSON.parse(IO.read(file_name))

puts json

Output:

{"some key": "some value", "some new key": "some new value"}

Bonus:

11. "\e[#{<color number>}m#{<some string>}\e[0m"

Changes color of string in shell based on ANSI escape code FG Code number

Example:

str = 'Hello world'
color_num = 36 # cyan

puts "\e[#{color_num}m#{str}\e[0m"

Output:

Hello world

Show me the code

Here’s the link to the repo

If you plan to create a similar tool, I suggest scanning around the repo (same link). It’s basically 4 files of Ruby code, and none of them exceed 100 lines. Hope that helps

Happy coding!

Like what you're seeing? Subscribe below to recieve notifications of new posts ⬇️

Promise not to send more than 1 email per month (not counting subscription confirmation email) 👨‍💻

Updated: 27 November, 2020
Created: 24 November, 2020