Pass by value vs. pass by reference

pass_by.rb

2.2.2 :001 > var1 = "hello"
 => "hello" 
2.2.2 :002 > var2 = var1
 => "hello" 
2.2.2 :004 > var2.upcase  
 => "HELLO" 
2.2.2 :005 > var2
 => "hello" 
2.2.2 :006 > var1
 => "hello" 
2.2.2 :007 > var2.upcase!
 => "HELLO" 
2.2.2 :008 > var1
 => "HELLO" 
2.2.2 :009 > var2
 => "HELLO" 


2.2.2 :001 > var1 = :symbol
 => :symbol 
2.2.2 :002 > var2 = var1
 => :symbol 
2.2.2 :003 > var1.to_s
 => "symbol" 
2.2.2 :004 > var1
 => :symbol 
2.2.2 :005 > var2
 => :symbol 
2.2.2 :006 > var1 = var1.to_s
 => "symbol" 
2.2.2 :007 > var2
 => :symbol 
2.2.2 :008 >