Kernel

The Kernel module is included by class Object, so its methods are available in every Ruby object.

The Kernel instance methods are documented in class Object while the module methods are documented here. These methods are called without a receiver and thus can be called in functional form:

sprintf "%.1f", 1.234 #=> "1.2"

What’s Here

Module Kernel provides methods that are useful for:

• Converting

• Querying

• Exiting

• Exceptions

• IO

• Procs

• Tracing

• Subprocesses

• Loading

• Yielding

• Random Values

• Other

Converting

• Array: Returns an Array based on the given argument.

• Complex: Returns a Complex based on the given arguments.

• Float: Returns a Float based on the given arguments.

• Hash: Returns a Hash based on the given argument.

• Integer: Returns an Integer based on the given arguments.

• Rational: Returns a Rational based on the given arguments.

• String: Returns a String based on the given argument.

Querying

• __callee__: Returns the called name of the current method as a symbol.

• __dir__: Returns the path to the directory from which the current method is called.

• __method__: Returns the name of the current method as a symbol.

• autoload?: Returns the file to be loaded when the given module is referenced.

• binding: Returns a Binding for the context at the point of call.

• block_given?: Returns true if a block was passed to the calling method.

• caller: Returns the current execution stack as an array of strings.

• caller_locations: Returns the current execution stack as an array of Thread::Backtrace::Location objects.

• class: Returns the class of self.

• frozen?: Returns whether self is frozen.

• global_variables: Returns an array of global variables as symbols.

• local_variables: Returns an array of local variables as symbols.

• test: Performs specified tests on the given single file or pair of files.

Exiting

• abort: Exits the current process after printing the given arguments.

• at_exit: Executes the given block when the process exits.

• exit: Exits the current process after calling any registered at_exit handlers.

• exit!: Exits the current process without calling any registered at_exit handlers.

Exceptions

• catch: Executes the given block, possibly catching a thrown object.

• raise (aliased as fail): Raises an exception based on the given arguments.

• throw: Returns from the active catch block waiting for the given tag.

IO

• ::pp: Prints the given objects in pretty form.

• gets: Returns and assigns to $_ the next line from the current input.

• open: Creates an IO object connected to the given stream, file, or subprocess.

• p: Prints the given objects’ inspect output to the standard output.

• print: Prints the given objects to standard output without a newline.

• printf: Prints the string resulting from applying the given format string to any additional arguments.

• putc: Equivalent to <tt.$stdout.putc(object)</tt> for the given object.

• puts: Equivalent to $stdout.puts(*objects) for the given objects.

• readline: Similar to gets, but raises an exception at the end of file.

• readlines: Returns an array of the remaining lines from the current input.

• select: Same as IO.select.

Procs

• lambda: Returns a lambda proc for the given block.

• proc: Returns a new Proc; equivalent to Proc.new.

Tracing

• set_trace_func: Sets the given proc as the handler for tracing, or disables tracing if given nil.

• trace_var: Starts tracing assignments to the given global variable.

• untrace_var: Disables tracing of assignments to the given global variable.

Subprocesses

• ‘command`: Returns the standard output of running command in a subshell.

• exec: Replaces current process with a new process.

• fork: Forks the current process into two processes.

• spawn: Executes the given command and returns its pid without waiting for completion.

• system: Executes the given command in a subshell.

Loading

• autoload: Registers the given file to be loaded when the given constant is first referenced.

• load: Loads the given Ruby file.

• require: Loads the given Ruby file unless it has already been loaded.

• require_relative: Loads the Ruby file path relative to the calling file, unless it has already been loaded.

Yielding

• tap: Yields self to the given block; returns self.

• then (aliased as yield_self): Yields self to the block and returns the result of the block.

Random Values

• rand: Returns a pseudo-random floating point number strictly between 0.0 and 1.0.

• srand: Seeds the pseudo-random number generator with the given number.

Other

• eval: Evaluates the given string as Ruby code.

• loop: Repeatedly executes the given block.

• sleep: Suspends the current thread for the given number of seconds.

• sprintf (aliased as format): Returns the string resulting from applying the given format string to any additional arguments.

• syscall: Runs an operating system call.

• trap: Specifies the handling of system signals.

• warn: Issue a warning based on the given messages and options.