Ruby offers conditional structures that are pretty common to modern languages. Here, we will explain all the conditional statements and modifiers available in Ruby.
Ruby if…else Statement
Syntax
if conditional [then] code...
[elsif conditional [then]
code…]…
[else
code…]
end
if expressions are used for conditional execution. The values false and nil are false, and everything else are true. Notice Ruby uses elsif, not else if nor elif.
Executes code if the conditional is true. If the conditional is not true, code specified in the else clause is executed.
An if expression’s conditional is separated from code by the reserved word then, a newline, or a semicolon.
Example
#!/usr/bin/ruby x = 1 if x > 2 puts "x is greater than 2" elsif x <= 2 and x!=0 puts "x is 1" else puts "I can't guess the number" end
x is 1
Ruby if modifier
Syntax
code if condition
Executes code if the conditional is true.
Example
#!/usr/bin/ruby $debug = 1 print "debug\n" if $debug
This will produce the following result −
debug
Ruby unless Statement
Syntax
unless conditional [then] code
[else
code ]
end
Executes code if conditional is false. If the conditional is true, code specified in the else clause is executed.
Example
#!/usr/bin/ruby x = 1 unless x>=2 puts "x is less than 2" else puts "x is greater than 2" end
This will produce the following result −
x is less than 2
Ruby unless modifier
Syntax
code unless conditional
Executes code if conditional is false.
Example
#!/usr/bin/ruby $var = 1 print "1 -- Value is set\n" if $var print "2 -- Value is set\n" unless $var $var = false print "3 -- Value is set\n" unless $var
This will produce the following result −
1 -- Value is set 3 -- Value is set
Ruby case Statement
Syntax
case expression [when expression [, expression ...] [then] code ]...
[else
code ]
end
Compares the expression specified by case and that specified by when using the === operator and executes the code of the when clause that matches.
The expression specified by the when clause is evaluated as the left operand. If no when clauses match, case executes the code of the else clause.
A when statement’s expression is separated from code by the reserved word then, a newline, or a semicolon. Thus −
case expr0 when expr1, expr2 stmt1 when expr3, expr4 stmt2 else stmt3 end
is basically similar to the following −
_tmp = expr0 if expr1 === _tmp || expr2 === _tmp stmt1 elsif expr3 === _tmp || expr4 === _tmp stmt2 else stmt3 end
Example
#!/usr/bin/ruby $age = 5 case $age when 0 .. 2 puts "baby" when 3 .. 6 puts "little child" when 7 .. 12 puts "child" when 13 .. 18 puts "youth" else puts "adult" end
This will produce the following result −
little child