Ruby - Modules 2020

We may want to prefer double quote("") to single quote(''). In the example below demonstrates when we have a variable within the quote, we should use double quote:

#!/usr/bin/ruby
# quote.rb
# How to quote

puts "Adding two numbers (4+5) = #{4+5} \n\n"
puts 'Adding two numbers (4+5) = #{4+5} \n\n'

Output:

$ ./quote.rb
Adding two numbers (4+5) = 9 

Adding two numbers (4+5) = #{4+5} \n\n

As we can see if we use single quote(''), it takes the string as literal, and does not replacing the variables.

How can we define a long string with several lines?

We'll use EOM to tell Ruby it's a multiline string:

#!/usr/bin/ruby
# multi.rb
# How to multiline string

long_string = <<EOM
This is a really long string
that requires several lines \n\n
EOM

puts long_string

Output:

$ ./multi.rb
This is a really long string 
that requires several lines 

In the following code, we do all sorts of operation on strings:

#!/usr/bin/ruby
# string.rb
# How to string operations

first_name = "Edwin"
last_name = "Hubble"

# simple string concatenation
full_name = first_name + last_name
puts "initial full_name = #{full_name}"

middle_name = "Powell"
# concatenate
full_name = "#{first_name} #{middle_name} #{last_name}"
puts "full_name with middle_name = #{full_name}"

# substring check
puts full_name.include?("Powell")

# string size
puts full_name.size

# counting the number of vowels and consonants
puts "Vowels : " + full_name.count("aeiou").to_s
puts "Consonants : " + full_name.count("^aeiou").to_s

# check start
puts full_name.start_with?("Hubble")

# index of a substring
puts "Index : " + full_name.index("Hubble").to_s

Output:

$ ./string.rb
initial full_name = EdwinHubble
full_name with middle_name = Edwin Powell Hubble
true
19
Vowels : 5
Consonants : 14
false
Index : 13

,equal? does object comparison. So, if same object it returns true.

#!/usr/bin/ruby
# comp.rb
# How to comparison operation with .equal?

# different objects
puts "\"a\".equal?(\"a\") : " + ("a".equal?"a").to_s

# same object
a = "a"
puts "a.equal?a : " + (a.equal?a).to_s

Output:

$ ./comp.rb
"a".equal?("a") : false
a.equal?a : true

We can control the cases:

#!/usr/bin/ruby
# case.rb
# How to case operations

full_name = "My full name"

puts full_name.upcase
puts full_name.downcase
puts full_name.swapcase

Output:

$ ./case.rb
MY FULL NAME
my full name
mY FULL NAME

Ruby has strip function for spaces: lstrip, rstrip, and strip.

#!/usr/bin/ruby
# strip.rb
# How to strip

name = "  myname"
puts "name.size = #{name.size}"
puts "name = #{name}"
puts
puts "name.lstrip = #{name.strip}"
puts "name.lstrip.size = #{name.lstrip.size}"
puts "name.strip = #{name.strip}"
puts "strip name.strip.size = #{name.strip.size}"
puts

name = "myname  "
puts "name = #{name}"
puts "name.size = #{name.size}"
puts "name.rstrip.size = #{name.rstrip.size}"

Output:

$ ./strip.rb
name.size = 8
name =   myname

name.lstrip = myname
name.lstrip.size = 6
name.strip = myname
strip name.strip.size = 6

name = myname  
name.size = 8
name.rstrip.size = 6

#!/usr/bin/ruby
# just.rb
# How to just

name = "Edwin Powell Hubble"

puts name.rjust(40,'.')
puts name.ljust(40,'.')
puts name.center(40,'.')

Output:

$ ./just.rb
.....................Edwin Powell Hubble
Edwin Powell Hubble.....................
..........Edwin Powell Hubble...........

#!/usr/bin/ruby
# chop.rb
# How to chop/chomp

name = "Edwin Powell Hubble"

# cut off the last chaaracter
puts name.chop

# cut off the given string
puts name.chomp('bble')
puts name.chomp('Hubble')

Output:

$ ./chop.rb
Edwin Powell Hubbl
Edwin Powell Hu
Edwin Powell 

In the example below, we'll split a string in two ways: 1. every character 2. space.

#!/usr/bin/ruby
# split.rb
# How to split

name = "Edwin Powell Hubble"

# split every character
array = name.split(//)
puts array

# split with a space as a delimiter
array = name.split(/ /)
puts array

Output:

$ ./split.rb
E
d
w
i
n
 
P
o
w
e
l
l
 
H
u
b
b
l
e
Edwin
Powell
Hubble