Loops in Ruby are used to execute the same block of code a specified number of times. This chapter details all the loop statements supported by Ruby.
Ruby while Statement
Syntax
while conditional [do] code end
Executes code while conditional is true. A while loop’s conditional is separated from code by the reserved word do, a newline, backslash \, or a semicolon ;.
Example
#!/usr/bin/ruby
$i = 0
$num = 5
while $i < $num do
puts("Inside the loop i = #$i" )
$i +=1
end
This will produce the following result −
Inside the loop i = 0 Inside the loop i = 1 Inside the loop i = 2 Inside the loop i = 3 Inside the loop i = 4
Ruby while modifier
Syntax
code while condition OR begin code end while conditional
Executes code while conditional is true.
If a while modifier follows a begin statement with no rescue or ensure clauses, code is executed once before conditional is evaluated.
Example
#!/usr/bin/ruby
$i = 0
$num = 5
begin
puts("Inside the loop i = #$i" )
$i +=1
end while $i < $num
This will produce the following result −
Inside the loop i = 0 Inside the loop i = 1 Inside the loop i = 2 Inside the loop i = 3 Inside the loop i = 4
Ruby until Statement
until conditional [do] code end
Executes code while conditional is false. An until statement’s conditional is separated from code by the reserved word do, a newline, or a semicolon.
Example
#!/usr/bin/ruby
$i = 0
$num = 5
until $i > $num do
puts("Inside the loop i = #$i" )
$i +=1;
end
This will produce the following result −
Inside the loop i = 0 Inside the loop i = 1 Inside the loop i = 2 Inside the loop i = 3 Inside the loop i = 4 Inside the loop i = 5
Ruby until modifier
Syntax
code until conditional OR begin code end until conditional
Executes code while conditional is false.
If an until modifier follows a begin statement with no rescue or ensure clauses, code is executed once before conditional is evaluated.
Example
#!/usr/bin/ruby
$i = 0
$num = 5
begin
puts("Inside the loop i = #$i" )
$i +=1;
end until $i > $num
This will produce the following result −
Inside the loop i = 0 Inside the loop i = 1 Inside the loop i = 2 Inside the loop i = 3 Inside the loop i = 4 Inside the loop i = 5
Ruby for Statement
Syntax
for variable [, variable ...] in expression [do] code end
Executes code once for each element in expression.
Example
#!/usr/bin/ruby
for i in 0..5
puts "Value of local variable is #{i}"
end
Here, we have defined the range 0..5. The statement for i in 0..5 will allow i to take values in the range from 0 to 5 (including 5). This will produce the following result −
Value of local variable is 0 Value of local variable is 1 Value of local variable is 2 Value of local variable is 3 Value of local variable is 4 Value of local variable is 5
A for…in loop is almost exactly equivalent to the following −
(expression).each do |variable[, variable...]| code end
except that a for loop doesn’t create a new scope for local variables. A for loop’s expression is separated from code by the reserved word do, a newline, or a semicolon.
Example
#!/usr/bin/ruby
(0..5).each do |i|
puts "Value of local variable is #{i}"
end
This will produce the following result −
Value of local variable is 0 Value of local variable is 1 Value of local variable is 2 Value of local variable is 3 Value of local variable is 4 Value of local variable is 5
Ruby break Statement
Syntax
break
Terminates the most internal loop. Terminates a method with an associated block if called within the block (with the method returning nil).
Example
#!/usr/bin/ruby
for i in 0..5
if i > 2 then
break
end
puts "Value of local variable is #{i}"
end
This will produce the following result −
Value of local variable is 0 Value of local variable is 1 Value of local variable is 2
Ruby next Statement
Syntax
next
Jumps to the next iteration of the most internal loop. Terminates execution of a block if called within a block (with yield or call returning nil).
Example
#!/usr/bin/ruby
for i in 0..5
if i < 2 then
next
end
puts "Value of local variable is #{i}"
end
This will produce the following result −
Value of local variable is 2 Value of local variable is 3 Value of local variable is 4 Value of local variable is 5
Ruby redo Statement
Syntax
redo
Restarts this iteration of the most internal loop, without checking loop condition. Restarts yield or call if called within a block.
Example
#!/usr/bin/ruby
for i in 0..5
if i < 2 then
puts "Value of local variable is #{i}"
redo
end
end
This will produce the following result and will go in an infinite loop −
Value of local variable is 0 Value of local variable is 0 ............................
Ruby retry Statement
Syntax
retry
If retry appears in rescue clause of begin expression, restart from the beginning of the begin body.
begin do_something # exception raised rescue # handles error retry # restart from beginning end
If retry appears in the iterator, the block, or the body of the for expression, restarts the invocation of the iterator call. Arguments to the iterator is re-evaluated.
for i in 1..5 retry if some_condition # restart from i == 1 end
Example
#!/usr/bin/ruby
for i in 0..5
retry if i > 2
puts "Value of local variable is #{i}"
end
This will produce the following result and will go in an infinite loop −
Value of local variable is 1 Value of local variable is 2 Value of local variable is 1 Value of local variable is 2 Value of local variable is 1 Value of local variable is 2 ............................