Ruby | Keywords

Keywords or Reserved words are the words in a language that are used for some internal process or represent some predefined actions. These words are therefore not allowed to use as variable names or objects or as constants. Doing this may result in compile-time error.

Example:

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# Ruby program to illustrate Keywords 
  
#!/usr/bin/ruby
  
# here 'if' is a keyword
# it can't be used as variable
if = 20
  
# Here 'if' and 'end' are keywords.  
# if condition to check whether  
# your age is enough for voting 
if if >= 18
  puts "You are eligible to vote."
end

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Compile Time Error:

Error(s), warning(s):

source_file.rb:7: syntax error, unexpected ‘=’
if = 20
^
source_file.rb:12: syntax error, unexpected >=
if if >= 18
^
source_file.rb:14: syntax error, unexpected keyword_end, expecting end-of-input

There are total 41 keywords present in Ruby as shown below:

Keyword Description
__ENCODING__ The script encoding of the current file.
__LINE__ The line number of this keyword in the current file.
__FILE__ The path to the current file.
BEGIN Runs before any other code in the current file.
END Runs after any other code in the current file.
alias Creates an alias between two methods (and other things).
and Short-circuit Boolean and with lower precedence than &&
begin Starts an exception handling block.
break Leaves a block early.
case Starts a case expression.
class Creates or opens a class.
def Defines a method.
defined? Returns a string describing its argument.
do Starts a block.
else The unhandled condition in case, if and unless expressions.
elsif An alternate condition for an if expression.
end The end of a syntax block. Used by classes, modules, methods, exception handling and control expressions.
ensure Starts a section of code that is always run when an exception is raised.
false Boolean false.
for A loop that is similar to using the each method.
if Used for if and modifier if expressions.
in Used to separate the iterable object and iterator variable in a for loop.
module Creates or opens a module.
next Skips the rest of the block.
nil A false value usually indicating “no value” or “unknown”.
not Inverts the following boolean expression. Has a lower precedence than !
or Boolean or with lower precedence than ||
redo Restarts execution in the current block.
rescue Starts an exception section of code in a begin block.
retry Retries an exception block.
return Exits a method.
self The object the current method is attached to.
super Calls the current method in a superclass.
then Indicates the end of conditional blocks in control structures.
true Boolean true.
undef Prevents a class or module from responding to a method call.
unless Used for unless and modifier unless expressions.
until Creates a loop that executes until the condition is true.
when A condition in a case expression.
while Creates a loop that executes while the condition is true.
yield Starts execution of the block sent to the current method.

Example:

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# Ruby program to illustrate the use of Keywords 
  
#!/usr/bin/ruby 
     
# defining class Vehicle 
# using the 'class' keyword
class GFG
     
# defining method 
# using 'def' keyword
def geeks 
     
    # printing result 
    puts "Hello Geeks!!"
     
# end of the method 
# using 'end' keyword
end
     
# end of class GFG 
# using 'end' keyword
end
     
# creating object 
obj = GFG.new
     
# calling method using object 
obj.geeks 

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Output:

Hello Geeks!!

Reference: http://ruby-doc.org/docs/keywords/1.9/Object.html



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