Keywords

__ENCODING__  # The script encoding of the current file
__END__       # Marks the end of the Ruby program; DATA can follow  
__FILE__      # The path to the current file
__LINE__      # The line number of this keyword in the current file

BEGIN         # Runs before any other code in the current file
END           # Runs after any other code in the current file
DATA          # An IO stream to read data embedded in the program following __END__

def           # Defines a method
defined?      # Returns a string describing its argument
do            # Starts a block
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.
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
send          # Invoke a method
__send__      # Alternative for the above, in case of name clashes
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