Ruby Input/Output, Objects, Load 2020

Let's learn how to get some input from a user and how to print it:

# r1.rb
# Reading input & printing output

print "Enter a number:"
num1 = gets.to_i
print "Enter another number:"
num2 = gets.to_i
puts num1.to_s + " + " + num2.to_s + " = " + (num1+num2).to_s

Output:

$ ruby r1.rb
Enter a number:10
Enter another number:20
10 + 20 = 30

Note that we used to_i and to_s for get method to convert a string to int or integer to string.

We can run the script as we do with shell script.

#!/usr/bin/ruby
# r1.rb
...

Then:

$ chmod +x r1.rb

$ ./r1.rb

#!/usr/bin/ruby
# r2.rb
# 5 Arithmetic operators

puts "7 + 3 = " + (7+3).to_s
puts "7 - 3 = " + (7-3).to_s
puts "7 * 3 = " + (7*3).to_s
puts "7 / 3 = " + (7/3).to_s
puts "7 % 3 = " + (7%3).to_s

Output:

$ ./r2.rb
7 + 3 = 10
7 - 3 = 4
7 * 3 = 21
7 / 3 = 2
7 % 3 = 1

#!/usr/bin/ruby
# r3.rb
# floating point numbers

num_one = 1.000
num_0999 = 0.999

puts "num_one - num_0999 = " + (num_one-num_0999).to_s

Output:

$ ./r3.rb
num_one - num_0999 = 0.0010000000000000009

Basically, everything in Ruby is an object.

#!/usr/bin/ruby
# r4.rb
# Objects

puts 1.class
puts 1.0123.class
puts "A string".class

Output:

./r4.rb
Fixnum
Float
String

We can create a file like this:

#!/usr/bin/ruby
# r6.rb
# File write

f = File.new("myfile.out","w")
f.puts("Test")
f.close

Output:

$ cat myfile.out 
Test

We can read from the file we created:

#!/usr/bin/ruby
# r7.rb
# File write / read

f = File.new("myfile.out","w")
f.puts("Test")
f.close

data = File.read("myfile.out")
puts "reading from a file data = " + data

Output:

$ ./r7.rb
reading from a file data = Test

We can load a Ruby file:

$ cat my_ruby.rb 
puts "Testing loading a 'rb' file"

Here is our code:

#!/usr/bin/ruby
# r8.rb
# loading 'rb' file

load "my_ruby.rb"

Output:

$ ./r8.rb
Testing loading a 'rb' file