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Module: Kernel

Relationships & Source Files
Extension / Inclusion / Inheritance Descendants
Included In:
Defined in: object.c,
complex.c,
cont.c,
eval.c,
eval_jump.c,
file.c,
io.c,
kernel.rb,
load.c,
object.c,
prelude.rb,
proc.c,
process.c,
random.c,
rational.c,
ruby.c,
signal.c,
vm_backtrace.c,
vm_eval.c,
vm_trace.c,
warning.rb

Overview

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.

Class Attribute Summary

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Class Attribute Details

block_given?Boolean (readonly)

Returns true if yield would execute a block in the current context. The .iterator? form is mildly deprecated.

def try
  if block_given?
    yield
  else
    "no block"
  end
end
try                  #=> "no block"
try { "hello" }      #=> "hello"
try do "hello" end   #=> "hello"
[ GitHub ]

  
# File 'vm_eval.c', line 2513

static VALUE
rb_f_block_given_p(VALUE _)
{
    rb_execution_context_t *ec = GET_EC();
    rb_control_frame_t *cfp = ec->cfp;
    cfp = vm_get_ruby_level_caller_cfp(ec, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));

    return RBOOL(cfp != NULL && VM_CF_BLOCK_HANDLER(cfp) != VM_BLOCK_HANDLER_NONE);
}

iterator?Boolean (readonly)

Deprecated. Use block_given? instead.

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# File 'vm_eval.c', line 2530

static VALUE
rb_f_iterator_p(VALUE self)
{
    rb_warn_deprecated("iterator?", "block_given?");
    return rb_f_block_given_p(self);
}

Class Method Details

__callee__Symbol

Returns the called name of the current method as a ::Symbol. If called outside of a method, it returns nil.

[ GitHub ]

  
# File 'eval.c', line 1923

static VALUE
rb_f_callee_name(VALUE _)
{
    ID fname = prev_frame_callee(); /* need *callee* ID */

    if (fname) {
	return ID2SYM(fname);
    }
    else {
	return Qnil;
    }
}

__dir__String

Returns the canonicalized absolute path of the directory of the file from which this method is called. It means symlinks in the path is resolved. If __FILE__ is nil, it returns nil. The return value equals to File.dirname(File.realpath(__FILE__)).

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# File 'eval.c', line 1946

static VALUE
f_current_dirname(VALUE _)
{
    VALUE base = rb_current_realfilepath();
    if (NIL_P(base)) {
	return Qnil;
    }
    base = rb_file_dirname(base);
    return base;
}

__method__Symbol

Returns the name at the definition of the current method as a ::Symbol. If called outside of a method, it returns nil.

[ GitHub ]

  
# File 'eval.c', line 1901

static VALUE
rb_f_method_name(VALUE _)
{
    ID fname = prev_frame_func(); /* need *method* ID */

    if (fname) {
	return ID2SYM(fname);
    }
    else {
	return Qnil;
    }
}

`String

Returns the $stdout output from running command in a subshell; sets global variable $? to the process status.

This method has potential security vulnerabilities if called with untrusted input; see Command Injection.

Examples:

$ `date`                 # => "Wed Apr  9 08:56:30 CDT 2003\n"
$ `echo oops && exit 99` # => "oops\n"
$ $?                     # => #<Process::Status: pid 17088 exit 99>
$ $?.status              # => 99>

The built-in syntax %x{...} uses this method.

[ GitHub ]

  
# File 'io.c', line 10156

static VALUE
rb_f_backquote(VALUE obj, VALUE str)
{
    VALUE port;
    VALUE result;
    rb_io_t *fptr;

    SafeStringValue(str);
    rb_last_status_clear();
    port = pipe_open_s(str, "r", FMODE_READABLE|DEFAULT_TEXTMODE, NULL);
    if (NIL_P(port)) return rb_str_new(0,0);

    GetOpenFile(port, fptr);
    result = read_all(fptr, remain_size(fptr), Qnil);
    rb_io_close(port);
    RFILE(port)->fptr = NULL;
    rb_io_fptr_finalize(fptr);
    RB_GC_GUARD(port);

    return result;
}

abort abort([msg]) Process.abort([msg])

Terminate execution immediately, effectively by calling Kernel.exit(false). If msg is given, it is written to STDERR prior to terminating.

[ GitHub ]

  
# File 'process.c', line 4584

static VALUE
f_abort(int c, const VALUE *a, VALUE _)
{
    rb_f_abort(c, a);
    UNREACHABLE_RETURN(Qnil);
}

Array(object) ⇒ Object, Array

Returns an array converted from object.

Tries to convert object to an array using to_ary first and to_a second:

Array([0, 1, 2])        # => [0, 1, 2]
Array({foo: 0, bar: 1}) # => [[:foo, 0], [:bar, 1]]
Array(0..4)             # => [0, 1, 2, 3, 4]

Returns object in an array, [object], if object cannot be converted:

Array(:foo)             # => [:foo]
[ GitHub ]

  
# File 'object.c', line 3745

static VALUE
rb_f_array(VALUE obj, VALUE arg)
{
    return rb_Array(arg);
}

at_exitProc

Converts block to a ::Proc object (and therefore binds it at the point of call) and registers it for execution when the program exits. If multiple handlers are registered, they are executed in reverse order of registration.

def do_at_exit(str1)
  at_exit { print str1 }
end
at_exit { puts "cruel world" }
do_at_exit("goodbye ")
exit

produces:

goodbye cruel world
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# File 'eval_jump.c', line 37

static VALUE
rb_f_at_exit(VALUE _)
{
    VALUE proc;

    if (!rb_block_given_p()) {
	rb_raise(rb_eArgError, "called without a block");
    }
    proc = rb_block_proc();
    rb_set_end_proc(rb_call_end_proc, proc);
    return proc;
}

autoload(const, filename) ⇒ nil

Registers filename to be loaded (using Kernel::require)

the first time that _const_ (which may be a String or
a symbol) is accessed.

   autoload(:MyModule, "/usr/local/lib/modules/my_module.rb")

If const is defined as autoload, the file name to be loaded is replaced with filename. If const is defined but not as autoload, does nothing.

[ GitHub ]

  
# File 'load.c', line 1387

static VALUE
rb_f_autoload(VALUE obj, VALUE sym, VALUE file)
{
    VALUE klass = rb_class_real(rb_vm_cbase());
    if (!klass) {
	rb_raise(rb_eTypeError, "Can not set autoload on singleton class");
    }
    return rb_mod_autoload(klass, sym, file);
}

autoload?(name, inherit = true) ⇒ String?

Returns filename to be loaded if name is registered as .autoload.

autoload(:B, "b")
autoload?(:B)            #=> "b"
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# File 'load.c', line 1408

static VALUE
rb_f_autoload_p(int argc, VALUE *argv, VALUE obj)
{
    /* use rb_vm_cbase() as same as rb_f_autoload. */
    VALUE klass = rb_vm_cbase();
    if (NIL_P(klass)) {
	return Qnil;
    }
    return rb_mod_autoload_p(argc, argv, klass);
}

bindingBinding

Returns a ::Binding object, describing the variable and method bindings at the point of call. This object can be used when calling .eval to execute the evaluated command in this environment. See also the description of class ::Binding.

def get_binding(param)
  binding
end
b = get_binding("hello")
eval("param", b)   #=> "hello"
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# File 'proc.c', line 404

static VALUE
rb_f_binding(VALUE self)
{
    return rb_binding_new();
}

callcc {|cont| ... } ⇒ Object

Generates a ::Continuation object, which it passes to the associated block. You need to require 'continuation' before using this method. Performing a cont.call will cause the #callcc to return (as will falling through the end of the block). The value returned by the #callcc is the value of the block, or the value passed to cont.call. See class ::Continuation for more details. Also see .throw for an alternative mechanism for unwinding a call stack.

[ GitHub ]

  
# File 'cont.c', line 1605

static VALUE
rb_callcc(VALUE self)
{
    volatile int called;
    volatile VALUE val = cont_capture(&called);

    if (called) {
        return val;
    }
    else {
        return rb_yield(val);
    }
}

caller(start = 1, length = nil) ⇒ Array? caller(range) ⇒ Array?

Returns the current execution stack—an array containing strings in the form file:line or file:line: in `method'.

The optional start parameter determines the number of initial stack entries to omit from the top of the stack.

A second optional length parameter can be used to limit how many entries are returned from the stack.

Returns nil if start is greater than the size of current execution stack.

Optionally you can pass a range, which will return an array containing the entries within the specified range.

def a(skip)
  caller(skip)
end
def b(skip)
  a(skip)
end
def c(skip)
  b(skip)
end
c(0)   #=> ["prog:2:in `a'", "prog:5:in `b'", "prog:8:in `c'", "prog:10:in `<main>'"]
c(1)   #=> ["prog:5:in `b'", "prog:8:in `c'", "prog:11:in `<main>'"]
c(2)   #=> ["prog:8:in `c'", "prog:12:in `<main>'"]
c(3)   #=> ["prog:13:in `<main>'"]
c(4)   #=> []
c(5)   #=> nil
[ GitHub ]

  
# File 'vm_backtrace.c', line 1227

static VALUE
rb_f_caller(int argc, VALUE *argv, VALUE _)
{
    return ec_backtrace_to_ary(GET_EC(), argc, argv, 1, 1, 1);
}

caller_locations(start = 1, length = nil) ⇒ Array? caller_locations(range) ⇒ Array?

Returns the current execution stack—an array containing backtrace location objects.

See ::Thread::Backtrace::Location for more information.

The optional start parameter determines the number of initial stack entries to omit from the top of the stack.

A second optional length parameter can be used to limit how many entries are returned from the stack.

Returns nil if start is greater than the size of current execution stack.

Optionally you can pass a range, which will return an array containing the entries within the specified range.

[ GitHub ]

  
# File 'vm_backtrace.c', line 1255

static VALUE
rb_f_caller_locations(int argc, VALUE *argv, VALUE _)
{
    return ec_backtrace_to_ary(GET_EC(), argc, argv, 1, 1, 0);
}

catch([tag]) {|tag| ... } ⇒ Object

catch executes its block. If .throw is not called, the block executes normally, and catch returns the value of the last expression evaluated.

catch(1) { 123 }            # => 123

If throw(tag2, val) is called, Ruby searches up its stack for a catch block whose tag has the same object_id as tag2. When found, the block stops executing and returns val (or nil if no second argument was given to .throw).

catch(1) { throw(1, 456) }  # => 456
catch(1) { throw(1) }       # => nil

When tag is passed as the first argument, catch yields it as the parameter of the block.

catch(1) {|x| x + 2 }       # => 3

When no tag is given, catch yields a new unique object (as from Object.new) as the block parameter. This object can then be used as the argument to .throw, and will match the correct catch block.

catch do |obj_A|
  catch do |obj_B|
    throw(obj_B, 123)
    puts "This puts is not reached"
  end

  puts "This puts is displayed"
  456
end

# => 456

catch do |obj_A|
  catch do |obj_B|
    throw(obj_A, 123)
    puts "This puts is still not reached"
  end

  puts "Now this puts is also not reached"
  456
end

# => 123
[ GitHub ]

  
# File 'vm_eval.c', line 2351

static VALUE
rb_f_catch(int argc, VALUE *argv, VALUE self)
{
    VALUE tag = rb_check_arity(argc, 0, 1) ? argv[0] : rb_obj_alloc(rb_cObject);
    return rb_catch_obj(tag, catch_i, 0);
}

chomp ⇒ $_ chomp(string) ⇒ $_

Equivalent to $_ = $_.chomp(string). See String#chomp. Available only when -p/-n command line option specified.

[ GitHub ]

  
# File 'ruby.c', line 1665

static VALUE
rb_f_chomp(int argc, VALUE *argv, VALUE _)
{
    VALUE str = rb_funcall_passing_block(uscore_get(), rb_intern("chomp"), argc, argv);
    rb_lastline_set(str);
    return str;
}

chop ⇒ $_

Equivalent to ($_.dup).chop!, except nil is never returned. See String#chop!. Available only when -p/-n command line option specified.

[ GitHub ]

  
# File 'ruby.c', line 1645

static VALUE
rb_f_chop(VALUE _)
{
    VALUE str = rb_funcall_passing_block(uscore_get(), rb_intern("chop"), 0, 0);
    rb_lastline_set(str);
    return str;
}

Complex(x[, y], exception: true) ⇒ Numeric?

Returns x+i*y;

Complex(1, 2)    #=> (1+2i)
Complex('1+2i')  #=> (1+2i)
Complex(nil)     #=> TypeError
Complex(1, nil)  #=> TypeError

Complex(1, nil, exception: false)  #=> nil
Complex('1+2', exception: false)   #=> nil

Syntax of string form:

string form = extra spaces , complex , extra spaces ;
complex = real part | [ sign ] , imaginary part
        | real part , sign , imaginary part
        | rational , "@" , rational ;
real part = rational ;
imaginary part = imaginary unit | unsigned rational , imaginary unit ;
rational = [ sign ] , unsigned rational ;
unsigned rational = numerator | numerator , "/" , denominator ;
numerator = integer part | fractional part | integer part , fractional part ;
denominator = digits ;
integer part = digits ;
fractional part = "." , digits , [ ( "e" | "E" ) , [ sign ] , digits ] ;
imaginary unit = "i" | "I" | "j" | "J" ;
sign = "-" | "+" ;
digits = digit , { digit | "_" , digit };
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
extra spaces = ? \s* ? ;

See String#to_c.

[ GitHub ]

  
# File 'complex.c', line 541

static VALUE
nucomp_f_complex(int argc, VALUE *argv, VALUE klass)
{
    VALUE a1, a2, opts = Qnil;
    int raise = TRUE;

    if (rb_scan_args(argc, argv, "11:", &a1, &a2, &opts) == 1) {
        a2 = Qundef;
    }
    if (!NIL_P(opts)) {
        raise = rb_opts_exception_p(opts, raise);
    }
    if (argc > 0 && CLASS_OF(a1) == rb_cComplex && a2 == Qundef) {
        return a1;
    }
    return nucomp_convert(rb_cComplex, a1, a2, raise);
}

eval(string [, binding [, filename [,lineno]]]) ⇒ Object

Evaluates the Ruby expression(s) in string. If binding is given, which must be a ::Binding object, the evaluation is performed in its context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.

def get_binding(str)
  return binding
end
str = "hello"
eval "str + ' Fred'"                      #=> "hello Fred"
eval "str + ' Fred'", get_binding("bye")  #=> "bye Fred"
[ GitHub ]

  
# File 'vm_eval.c', line 1801

VALUE
rb_f_eval(int argc, const VALUE *argv, VALUE self)
{
    VALUE src, scope, vfile, vline;
    VALUE file = Qundef;
    int line = 1;

    rb_scan_args(argc, argv, "13", &src, &scope, &vfile, &vline);
    SafeStringValue(src);
    if (argc >= 3) {
	StringValue(vfile);
    }
    if (argc >= 4) {
	line = NUM2INT(vline);
    }

    if (!NIL_P(vfile))
	file = vfile;

    if (NIL_P(scope))
	return eval_string_with_cref(self, src, NULL, file, line);
    else
	return eval_string_with_scope(scope, src, file, line);
}

exec([env,] command... [,options])

Replaces the current process by running the given external command, which can take one of the following forms:

exec(commandline)

command line string which is passed to the standard shell

exec(cmdname, arg1, ...)

command name and one or more arguments (no shell)

exec([cmdname, argv0], arg1, ...)

command name, argv[0] and zero or more arguments (no shell)

In the first form, the string is taken as a command line that is subject to shell expansion before being executed.

The standard shell always means "/bin/sh" on Unix-like systems, otherwise, ENV["RUBYSHELL"] or ENV["COMSPEC"] on Windows and similar. The command is passed as an argument to the "-c" switch to the shell, except in the case of COMSPEC.

If the string from the first form (exec("command")) follows these simple rules:

  • no meta characters

  • not starting with shell reserved word or special built-in

  • Ruby invokes the command directly without shell

You can force shell invocation by adding “;” to the string (because “;” is a meta character).

Note that this behavior is observable by pid obtained (return value of spawn() and IO#pid for IO.popen) is the pid of the invoked command, not shell.

In the second form (exec("command1", "arg1", ...)), the first is taken as a command name and the rest are passed as parameters to command with no shell expansion.

In the third form (exec(["command", "argv0"], "arg1", ...)), starting a two-element array at the beginning of the command, the first element is the command to be executed, and the second argument is used as the argv[0] value, which may show up in process listings.

In order to execute the command, one of the exec(2) system calls are used, so the running command may inherit some of the environment of the original program (including open file descriptors).

This behavior is modified by the given env and options parameters. See .spawn for details.

If the command fails to execute (typically Errno::ENOENT when it was not found) a ::SystemCallError exception is raised.

This method modifies process attributes according to given options before exec(2) system call. See .spawn for more details about the given options.

The modified attributes may be retained when exec(2) system call fails.

For example, hard resource limits are not restorable.

Consider to create a child process using .spawn or .system if this is not acceptable.

exec "echo *"       # echoes list of files in current directory
# never get here

exec "echo", "*"    # echoes an asterisk
# never get here
[ GitHub ]

  
# File 'process.c', line 3196

static VALUE
f_exec(int c, const VALUE *a, VALUE _)
{
    rb_f_exec(c, a);
    UNREACHABLE_RETURN(Qnil);
}

exit(status = true) exit(status = true) Process.exit(status = true)

Initiates the termination of the Ruby script by raising the ::SystemExit exception. This exception may be caught. The optional parameter is used to return a status code to the invoking environment. true and FALSE of status means success and failure respectively. The interpretation of other integer values are system dependent.

begin
  exit
  puts "never get here"
rescue SystemExit
  puts "rescued a SystemExit exception"
end
puts "after begin block"

produces:

rescued a SystemExit exception
after begin block

Just prior to termination, Ruby executes any .at_exit functions (see .at_exit) and runs any object finalizers (see ObjectSpace.define_finalizer).

at_exit { puts "at_exit function" }
ObjectSpace.define_finalizer("string",  proc { puts "in finalizer" })
exit

produces:

at_exit function
in finalizer
[ GitHub ]

  
# File 'process.c', line 4539

static VALUE
f_exit(int c, const VALUE *a, VALUE _)
{
    rb_f_exit(c, a);
    UNREACHABLE_RETURN(Qnil);
}

Process.exit!(status = false)

Exits the process immediately. No exit handlers are run. status is returned to the underlying system as the exit status.

Process.exit!(true)
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# File 'process.c', line 4452

static VALUE
rb_f_exit_bang(int argc, VALUE *argv, VALUE obj)
{
    int istatus;

    if (rb_check_arity(argc, 0, 1) == 1) {
	istatus = exit_status_code(argv[0]);
    }
    else {
	istatus = EXIT_FAILURE;
    }
    _exit(istatus);

    UNREACHABLE_RETURN(Qnil);
}

raise raise(string, cause: $!) raise(exception [, string [, array]], cause: $!) fail fail(string, cause: $!) fail(exception [, string [, array]], cause: $!)
Also known as: .raise

With no arguments, raises the exception in $! or raises a ::RuntimeError if $! is nil. With a single .String argument, raises a ::RuntimeError with the string as a message. Otherwise, the first parameter should be an ::Exception class (or another object that returns an ::Exception object when sent an exception message). The optional second parameter sets the message associated with the exception (accessible via Exception#message), and the third parameter is an array of callback information (accessible via Exception#backtrace). The cause of the generated exception (accessible via Exception#cause) is automatically set to the “current” exception ($!), if any. An alternative value, either an ::Exception object or nil, can be specified via the :cause argument.

Exceptions are caught by the rescue clause of begin...end blocks.

raise "Failed to create socket"
raise ArgumentError, "No parameters", caller
[ GitHub ]

  
# File 'eval.c', line 771

static VALUE
f_raise(int c, VALUE *v, VALUE _)
{
    return rb_f_raise(c, v);
}

Float(arg, exception: true) ⇒ Float? (mod_func)

Returns arg converted to a float. ::Numeric types are converted directly, and with exception to .String and nil the rest are converted using arg.to_f. Converting a .String with invalid characters will result in a ::ArgumentError. Converting nil generates a ::TypeError. Exceptions can be suppressed by passing exception: false.

Float(1)                 #=> 1.0
Float("123.456")         #=> 123.456
Float("123.0_badstring") #=> ArgumentError: invalid value for Float(): "123.0_badstring"
Float(nil)               #=> TypeError: can't convert nil into Float
Float("123.0_badstring", exception: false)  #=> nil
[ GitHub ]

  
# File 'kernel.rb', line 171

def Float(arg, exception: true)
  if Primitive.mandatory_only?
    Primitive.rb_f_float1(arg)
  else
    Primitive.rb_f_float(arg, exception)
  end
end

forkInteger? forkInteger? Process.forkInteger? Process.forkInteger?

Creates a subprocess. If a block is specified, that block is run in the subprocess, and the subprocess terminates with a status of zero. Otherwise, the fork call returns twice, once in the parent, returning the process ID of the child, and once in the child, returning nil. The child process can exit using .exit! to avoid running any .at_exit functions. The parent process should use Process.wait to collect the termination statuses of its children or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.

The thread calling fork is the only thread in the created child process. fork doesn’t copy other threads.

If fork is not usable, Process.respond_to?(:fork) returns false.

Note that fork(2) is not available on some platforms like Windows and NetBSD 4. Therefore you should use spawn() instead of fork().

[ GitHub ]

  
# File 'process.c', line 4394

static VALUE
rb_f_fork(VALUE obj)
{
    rb_pid_t pid;

    pid = rb_call_proc__fork();

    if (pid == 0) {
	if (rb_block_given_p()) {
	    int status;
	    rb_protect(rb_yield, Qundef, &status);
	    ruby_stop(status);
	}
	return Qnil;
    }

    return PIDT2NUM(pid);
}

format(format_string *objects) ⇒ String Also known as: .sprintf

Returns the string resulting from formatting objects into format_string.

For details on format_string, see Format Specifications.

format is an alias for .sprintf.

[ GitHub ]

  
# File 'object.c', line 3878

static VALUE
f_sprintf(int c, const VALUE *v, VALUE _)
{
    return rb_f_sprintf(c, v);
}

gets(sep=$/ [, getline_args]) ⇒ String? gets(limit [, getline_args]) ⇒ String? gets(sep, limit [, getline_args]) ⇒ String?

Returns (and assigns to $_) the next line from the list of files in ARGV (or $*), or from standard input if no files are present on the command line. Returns nil at end of file. The optional argument specifies the record separator. The separator is included with the contents of each record. A separator of nil reads the entire contents, and a zero-length separator reads the input one paragraph at a time, where paragraphs are divided by two consecutive newlines. If the first argument is an integer, or optional second argument is given, the returning string would not be longer than the given value in bytes. If multiple filenames are present in ARGV, gets(nil) will read the contents one file at a time.

ARGV << "testfile"
print while gets

produces:

This is line one
This is line two
This is line three
And so on...

The style of programming using $_ as an implicit parameter is gradually losing favor in the Ruby community.

[ GitHub ]

  
# File 'io.c', line 9902

static VALUE
rb_f_gets(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_gets(argc, argv, argf);
    }
    return forward(argf, idGets, argc, argv);
}

global_variablesArray

Returns an array of the names of global variables. This includes special regexp global variables such as $~ and $+, but does not include the numbered regexp global variables ($1, $2, etc.).

global_variables.grep /std/   #=> [:$stdin, :$stdout, :$stderr]
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# File 'eval.c', line 1969

static VALUE
f_global_variables(VALUE _)
{
    return rb_f_global_variables();
}

gsub(pattern, replacement) ⇒ $_ gsub(pattern) {|...| ... } ⇒ $_

Equivalent to $_.gsub..., except that $_ will be updated if substitution occurs. Available only when -p/-n command line option specified.

[ GitHub ]

  
# File 'ruby.c', line 1627

static VALUE
rb_f_gsub(int argc, VALUE *argv, VALUE _)
{
    VALUE str = rb_funcall_passing_block(uscore_get(), rb_intern("gsub"), argc, argv);
    rb_lastline_set(str);
    return str;
}

Hash(object) ⇒ Object, Hash

Returns a hash converted from object.

  • If object is:

    • A hash, returns object.

    • An empty array or nil, returns an empty hash.

  • Otherwise, if object.to_hash returns a hash, returns that hash.

  • Otherwise, returns ::TypeError.

Examples:

Hash({foo: 0, bar: 1}) # => {:foo=>0, :bar=>1}
Hash(nil)              # => {}
Hash([])               # => {}
[ GitHub ]

  
# File 'object.c', line 3791

static VALUE
rb_f_hash(VALUE obj, VALUE arg)
{
    return rb_Hash(arg);
}

Integer(object, base = 0, exception: true) ⇒ Integer?

Returns an integer converted from object.

Tries to convert object to an integer using to_int first and to_i second; see below for exceptions.

With integer argument object given, returns object:

Integer(1)                # => 1
Integer(-1)               # => -1

With floating-point argument object given, returns object truncated to an intger:

Integer(1.9)              # => 1  # Rounds toward zero.
Integer(-1.9)             # => -1 # Rounds toward zero.

With string argument object and zero base given, returns object converted to an integer in base 10:

Integer('100')    # => 100
Integer('-100')   # => -100

With base zero, string object may contain leading characters to specify the actual base:

Integer('0100')  # => 64  # Leading '0' specifies base 8.
Integer('0b100') # => 4   # Leading '0b', specifies base 2.
Integer('0x100') # => 256 # Leading '0x' specifies base 16.

With a non-zero base (in range 2..36) given (in which case object must be a string), returns object converted to an integer in the given base:

Integer('100', 2)   # => 4
Integer('100', 8)   # => 64
Integer('-100', 16) # => -256

When converting strings, surrounding whitespace and embedded underscores are allowed and ignored:

Integer(' 100 ')      # => 100
Integer('-1_0_0', 16) # => -256

Examples with object of various other classes:

Integer(Rational(9, 10)) # => 0  # Rounds toward zero.
Integer(Complex(2, 0))   # => 2  # Imaginary part must be zero.
Integer(Time.now)        # => 1650974042

With optional keyword argument exception given as true (the default):

  • Raises TypeError if object does not respond to to_int or to_i.

  • Raises TypeError if object is nil.

  • Raise ArgumentError if object is an invalid string.

With exception given as false, an exception of any kind is suppressed and nil is returned.

[ GitHub ]

  
# File 'object.c', line 3256

static VALUE
rb_f_integer(int argc, VALUE *argv, VALUE obj)
{
    VALUE arg = Qnil, opts = Qnil;
    int base = 0;

    if (argc > 1) {
        int narg = 1;
        VALUE vbase = rb_check_to_int(argv[1]);
        if (!NIL_P(vbase)) {
            base = NUM2INT(vbase);
            narg = 2;
        }
        if (argc > narg) {
            VALUE hash = rb_check_hash_type(argv[argc-1]);
            if (!NIL_P(hash)) {
                opts = rb_extract_keywords(&hash);
                if (!hash) --argc;
            }
        }
    }
    rb_check_arity(argc, 1, 2);
    arg = argv[0];

    return rb_convert_to_integer(arg, base, opts_exception_p(opts));
}

lambda {|...| ... } ⇒ Proc

Equivalent to Proc.new, except the resulting ::Proc objects check the number of parameters passed when called.

[ GitHub ]

  
# File 'proc.c', line 905

static VALUE
f_lambda(VALUE _)
{
    f_lambda_warn();
    return rb_block_lambda();
}

load(filename, wrap = false) ⇒ true

Loads and executes the Ruby program in the file filename.

If the filename is an absolute path (e.g. starts with ‘/’), the file will be loaded directly using the absolute path.

If the filename is an explicit relative path (e.g. starts with ‘./’ or ‘../’), the file will be loaded using the relative path from the current directory.

Otherwise, the file will be searched for in the library directories listed in $LOAD_PATH ($:). If the file is found in a directory, it will attempt to load the file relative to that directory. If the file is not found in any of the directories in $LOAD_PATH, the file will be loaded using the relative path from the current directory.

If the file doesn’t exist when there is an attempt to load it, a ::LoadError will be raised.

If the optional wrap parameter is true, the loaded script will be executed under an anonymous module, protecting the calling program’s global namespace. If the optional wrap parameter is a module, the loaded script will be executed under the given module. In no circumstance will any local variables in the loaded file be propagated to the loading environment.

[ GitHub ]

  
# File 'load.c', line 812

static VALUE
rb_f_load(int argc, VALUE *argv, VALUE _)
{
    VALUE fname, wrap, path, orig_fname;

    rb_scan_args(argc, argv, "11", &fname, &wrap);

    orig_fname = rb_get_path_check_to_string(fname);
    fname = rb_str_encode_ospath(orig_fname);
    RUBY_DTRACE_HOOK(LOAD_ENTRY, RSTRING_PTR(orig_fname));

    path = rb_find_file(fname);
    if (!path) {
	if (!rb_file_load_ok(RSTRING_PTR(fname)))
	    load_failed(orig_fname);
	path = fname;
    }
    rb_load_internal(path, wrap);

    RUBY_DTRACE_HOOK(LOAD_RETURN, RSTRING_PTR(orig_fname));

    return Qtrue;
}

local_variablesArray

Returns the names of the current local variables.

fred = 1
for i in 1..10
   # ...
end
local_variables   #=> [:fred, :i]
[ GitHub ]

  
# File 'vm_eval.c', line 2458

static VALUE
rb_f_local_variables(VALUE _)
{
    struct local_var_list vars;
    rb_execution_context_t *ec = GET_EC();
    rb_control_frame_t *cfp = vm_get_ruby_level_caller_cfp(ec, RUBY_VM_PREVIOUS_CONTROL_FRAME(ec->cfp));
    unsigned int i;

    local_var_list_init(&vars);
    while (cfp) {
	if (cfp->iseq) {
            for (i = 0; i < ISEQ_BODY(cfp->iseq)->local_table_size; i++) {
                local_var_list_add(&vars, ISEQ_BODY(cfp->iseq)->local_table[i]);
	    }
	}
	if (!VM_ENV_LOCAL_P(cfp->ep)) {
	    /* block */
	    const VALUE *ep = VM_CF_PREV_EP(cfp);

	    if (vm_collect_local_variables_in_heap(ep, &vars)) {
		break;
	    }
	    else {
		while (cfp->ep != ep) {
		    cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
		}
	    }
	}
	else {
	    break;
	}
    }
    return local_var_list_finish(&vars);
}

loop loopEnumerator

Repeatedly executes the block.

If no block is given, an enumerator is returned instead.

loop do
  print "Input: "
  line = gets
  break if !line or line =~ /^qQ/
  # ...
end

::StopIteration raised in the block breaks the loop. In this case, loop returns the “result” value stored in the exception.

enum = Enumerator.new { |y|
  y << "one"
  y << "two"
  :ok
}

result = loop {
  puts enum.next
} #=> :ok
[ GitHub ]

  
# File 'vm_eval.c', line 1493

static VALUE
rb_f_loop(VALUE self)
{
    RETURN_SIZED_ENUMERATOR(self, 0, 0, rb_f_loop_size);
    return rb_rescue2(loop_i, (VALUE)0, loop_stop, (VALUE)0, rb_eStopIteration, (VALUE)0);
}

open(path, mode = 'r', perm = 0666, **opts) ⇒ IO? open(path, mode = 'r', perm = 0666, **opts) {|io| ... } ⇒ Object

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

Required string argument path determines which of the following occurs:

  • The file at the specified path is opened.

  • The process forks.

  • A subprocess is created.

Each of these is detailed below.

File Opened

If path does not start with a pipe character ('|'), a file stream is opened with File.open(path, mode, perm, **opts).

With no block given, file stream is returned:

open('t.txt') # => #<File:t.txt>

With a block given, calls the block with the open file stream, then closes the stream:

open('t.txt') {|f| p f } # => #<File:t.txt (closed)>

Output:

#<File:t.txt>

See File.open for details.

Process Forked

If path is the 2-character string '|-', the process forks and the child process is connected to the parent.

With no block given:

io = open('|-')
if io
  $stderr.puts "In parent, child pid is #{io.pid}."
else
  $stderr.puts "In child, pid is #{$$}."
end

Output:

In parent, child pid is 27903.
In child, pid is 27903.

With a block given:

open('|-') do |io|
  if io
    $stderr.puts "In parent, child pid is #{io.pid}."
  else
    $stderr.puts "In child, pid is #{$$}."
  end
end

Output:

In parent, child pid is 28427.
In child, pid is 28427.

Subprocess Created

If path is '|command' ('command' != '-'), a new subprocess runs the command; its open stream is returned. Note that the command may be processed by shell if it contains shell metacharacters.

With no block given:

io = open('|echo "Hi!"') # => #<IO:fd 12>
print io.gets
io.close

Output:

"Hi!"

With a block given, calls the block with the stream, then closes the stream:

open('|echo "Hi!"') do |io|
  print io.gets
end

Output:

"Hi!"
[ GitHub ]

  
# File 'io.c', line 7914

static VALUE
rb_f_open(int argc, VALUE *argv, VALUE _)
{
    ID to_open = 0;
    int redirect = FALSE;

    if (argc >= 1) {
	CONST_ID(to_open, "to_open");
	if (rb_respond_to(argv[0], to_open)) {
	    redirect = TRUE;
	}
	else {
	    VALUE tmp = argv[0];
	    FilePathValue(tmp);
	    if (NIL_P(tmp)) {
		redirect = TRUE;
	    }
	    else {
                VALUE cmd = check_pipe_command(tmp);
                if (!NIL_P(cmd)) {
		    argv[0] = cmd;
		    return rb_io_s_popen(argc, argv, rb_cIO);
		}
	    }
	}
    }
    if (redirect) {
        VALUE io = rb_funcallv_kw(argv[0], to_open, argc-1, argv+1, RB_PASS_CALLED_KEYWORDS);

	if (rb_block_given_p()) {
	    return rb_ensure(rb_yield, io, io_close, io);
	}
	return io;
    }
    return rb_io_s_open(argc, argv, rb_cFile);
}

p(object) ⇒ Object p(*objects) ⇒ array of objects pnil

For each object obj, executes:

$stdout.write(obj.inspect, "\n")

With one object given, returns the object; with multiple objects given, returns an array containing the objects; with no object given, returns nil.

Examples:

r = Range.new(0, 4)
p r                 # => 0..4
p [r, r, r]         # => [0..4, 0..4, 0..4]
p                   # => nil

Output:

0..4
[0..4, 0..4, 0..4]
[ GitHub ]

  
# File 'io.c', line 8727

static VALUE
rb_f_p(int argc, VALUE *argv, VALUE self)
{
    int i;
    for (i=0; i<argc; i++) {
        VALUE inspected = rb_obj_as_string(rb_inspect(argv[i]));
        rb_uninterruptible(rb_p_write, inspected);
    }
    return rb_p_result(argc, argv);
}

printf(format_string, *objects) ⇒ nil printf(io, format_string, *objects) ⇒ nil

Equivalent to:

io.write(sprintf(format_string, *objects))

For details on format_string, see Format Specifications.

With the single argument format_string, formats objects into the string, then writes the formatted string to $stdout:

printf('%4.4d %10s %2.2f', 24, 24, 24.0)

Output (on $stdout):

0024         24 24.00#

With arguments io and format_string, formats objects into the string, then writes the formatted string to io:

printf($stderr, '%4.4d %10s %2.2f', 24, 24, 24.0)

Output (on $stderr):

0024         24 24.00# => nil

With no arguments, does nothing.

[ GitHub ]

  
# File 'io.c', line 8292

static VALUE
rb_f_printf(int argc, VALUE *argv, VALUE _)
{
    VALUE out;

    if (argc == 0) return Qnil;
    if (RB_TYPE_P(argv[0], T_STRING)) {
	out = rb_ractor_stdout();
    }
    else {
	out = argv[0];
	argv++;
	argc--;
    }
    rb_io_write(out, rb_f_sprintf(argc, argv));

    return Qnil;
}

proc {|...| ... } ⇒ Proc

Equivalent to Proc.new.

[ GitHub ]

  
# File 'proc.c', line 857

static VALUE
f_proc(VALUE _)
{
    return proc_new(rb_cProc, FALSE, TRUE);
}

putc(int) ⇒ Integer

Equivalent to:

$stdout.putc(int)

See IO#putc for important information regarding multi-byte characters.

[ GitHub ]

  
# File 'io.c', line 8514

static VALUE
rb_f_putc(VALUE recv, VALUE ch)
{
    VALUE r_stdout = rb_ractor_stdout();
    if (recv == r_stdout) {
	return rb_io_putc(recv, ch);
    }
    return forward(r_stdout, rb_intern("putc"), 1, &ch);
}

puts(*objects) ⇒ nil

Equivalent to

$stdout.puts(objects)
[ GitHub ]

  
# File 'io.c', line 8648

static VALUE
rb_f_puts(int argc, VALUE *argv, VALUE recv)
{
    VALUE r_stdout = rb_ractor_stdout();
    if (recv == r_stdout) {
	return rb_io_puts(argc, argv, recv);
    }
    return forward(r_stdout, rb_intern("puts"), argc, argv);
}

raise raise(string, cause: $!) raise(exception [, string [, array]], cause: $!) fail fail(string, cause: $!) fail(exception [, string [, array]], cause: $!)

Alias for .fail.

rand(max = 0) ⇒ Numeric

If called without an argument, or if max.to_i.abs == 0, rand returns a pseudo-random floating point number between 0.0 and 1.0, including 0.0 and excluding 1.0.

rand        #=> 0.2725926052826416

When max.abs is greater than or equal to 1, rand returns a pseudo-random integer greater than or equal to 0 and less than max.to_i.abs.

rand(100)   #=> 12

When max is a ::Range, rand returns a random number where range.member?(number) == true.

Negative or floating point values for max are allowed, but may give surprising results.

rand(-100) # => 87
rand(-0.5) # => 0.8130921818028143
rand(1.9)  # equivalent to rand(1), which is always 0

.srand may be used to ensure that sequences of random numbers are reproducible between different runs of a program.

See also Random.rand.

[ GitHub ]

  
# File 'random.c', line 1640

static VALUE
rb_f_rand(int argc, VALUE *argv, VALUE obj)
{
    VALUE vmax;
    rb_random_t *rnd = rand_start(default_rand());

    if (rb_check_arity(argc, 0, 1) && !NIL_P(vmax = argv[0])) {
        VALUE v = rand_range(obj, rnd, vmax);
	if (v != Qfalse) return v;
	vmax = rb_to_int(vmax);
	if (vmax != INT2FIX(0)) {
            v = rand_int(obj, rnd, vmax, 0);
	    if (!NIL_P(v)) return v;
	}
    }
    return DBL2NUM(random_real(obj, rnd, TRUE));
}

Rational(x, y, exception: true) ⇒ Rational? Rational(arg, exception: true) ⇒ Rational?

Returns x/y or arg as a Rational.

Rational(2, 3)   #=> (2/3)
Rational(5)      #=> (5/1)
Rational(0.5)    #=> (1/2)
Rational(0.3)    #=> (5404319552844595/18014398509481984)

Rational("2/3")  #=> (2/3)
Rational("0.3")  #=> (3/10)

Rational("10 cents")  #=> ArgumentError
Rational(nil)         #=> TypeError
Rational(1, nil)      #=> TypeError

Rational("10 cents", exception: false)  #=> nil

Syntax of the string form:

string form = extra spaces , rational , extra spaces ;
rational = [ sign ] , unsigned rational ;
unsigned rational = numerator | numerator , "/" , denominator ;
numerator = integer part | fractional part | integer part , fractional part ;
denominator = digits ;
integer part = digits ;
fractional part = "." , digits , [ ( "e" | "E" ) , [ sign ] , digits ] ;
sign = "-" | "+" ;
digits = digit , { digit | "_" , digit } ;
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
extra spaces = ? \s* ? ;

See also String#to_r.

[ GitHub ]

  
# File 'rational.c', line 552

static VALUE
nurat_f_rational(int argc, VALUE *argv, VALUE klass)
{
    VALUE a1, a2, opts = Qnil;
    int raise = TRUE;

    if (rb_scan_args(argc, argv, "11:", &a1, &a2, &opts) == 1) {
        a2 = Qundef;
    }
    if (!NIL_P(opts)) {
        raise = rb_opts_exception_p(opts, raise);
    }
    return nurat_convert(rb_cRational, a1, a2, raise);
}

readline(sep = $/, **line_opts) ⇒ String readline(limit, **line_opts) ⇒ String readline(sep, limit, **line_opts) ⇒ String

Equivalent to method .gets, except that it raises an exception if called at end-of-stream:

$ cat t.txt | ruby -e "p readlines; readline"
["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
in `readline': end of file reached (EOFError)
[ GitHub ]

  
# File 'io.c', line 9983

static VALUE
rb_f_readline(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_readline(argc, argv, argf);
    }
    return forward(argf, rb_intern("readline"), argc, argv);
}

readlines(sep = $/, **line_opts) ⇒ Array readlines(limit, **line_opts) ⇒ Array readlines(sep, limit, **line_opts) ⇒ Array

Returns an array containing the lines returned by calling .gets until the end-of-file is reached; (see Lines).

With only string argument sep given, returns the remaining lines as determined by line separator sep, or nil if none; see Line Separator:

# Default separator.
$ cat t.txt | ruby -e "p readlines"
["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]

# Specified separator.
$ cat t.txt | ruby -e "p readlines 'li'"
["First li", "ne\nSecond li", "ne\n\nFourth li", "ne\nFifth li", "ne\n"]

# Get-all separator.
$ cat t.txt | ruby -e "p readlines nil"
["First line\nSecond line\n\nFourth line\nFifth line\n"]

# Get-paragraph separator.
$ cat t.txt | ruby -e "p readlines ''"
["First line\nSecond line\n\n", "Fourth line\nFifth line\n"]

With only integer argument limit given, limits the number of bytes in the line; see Line Limit:

$cat t.txt | ruby -e "p readlines 10"
["First line", "\n", "Second lin", "e\n", "\n", "Fourth lin", "e\n", "Fifth line", "\n"]

$cat t.txt | ruby -e "p readlines 11"
["First line\n", "Second line", "\n", "\n", "Fourth line", "\n", "Fifth line\n"]

$cat t.txt | ruby -e "p readlines 12"
["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]

With arguments sep and limit given, combines the two behaviors; see Line Separator and Line Limit.

For all forms above, optional keyword arguments specify:

  • Line Options.

  • {Encoding options}.

Examples:

$ cat t.txt | ruby -e "p readlines(chomp: true)"
["First line", "Second line", "", "Fourth line", "Fifth line"]
[ GitHub ]

  
# File 'io.c', line 10086

static VALUE
rb_f_readlines(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_readlines(argc, argv, argf);
    }
    return forward(argf, rb_intern("readlines"), argc, argv);
}

require(name) ⇒ Boolean

Loads the given name, returning true if successful and false if the feature is already loaded.

If the filename neither resolves to an absolute path nor starts with ‘./’ or ‘../’, the file will be searched for in the library directories listed in $LOAD_PATH ($:). If the filename starts with ‘./’ or ‘../’, resolution is based on Dir.pwd.

If the filename has the extension “.rb”, it is loaded as a source file; if the extension is “.so”, “.o”, or “.dll”, or the default shared library extension on the current platform, Ruby loads the shared library as a Ruby extension. Otherwise, Ruby tries adding “.rb”, “.so”, and so on to the name until found. If the file named cannot be found, a ::LoadError will be raised.

For Ruby extensions the filename given may use any shared library extension. For example, on Linux the socket extension is “socket.so” and require 'socket.dll' will load the socket extension.

The absolute path of the loaded file is added to $LOADED_FEATURES ($"). A file will not be loaded again if its path already appears in $". For example, require 'a'; require './a' will not load a.rb again.

require "my-library.rb"
require "db-driver"

Any constants or globals within the loaded source file will be available in the calling program’s global namespace. However, local variables will not be propagated to the loading environment.

[ GitHub ]

  
# File 'load.c', line 938

VALUE
rb_f_require(VALUE obj, VALUE fname)
{
    return rb_require_string(fname);
}

require_relative(string) ⇒ Boolean

Ruby tries to load the library named string relative to the directory containing the requiring file. If the file does not exist a ::LoadError is raised. Returns true if the file was loaded and false if the file was already loaded before.

[ GitHub ]

  
# File 'load.c', line 953

VALUE
rb_f_require_relative(VALUE obj, VALUE fname)
{
    VALUE base = rb_current_realfilepath();
    if (NIL_P(base)) {
	rb_loaderror("cannot infer basepath");
    }
    base = rb_file_dirname(base);
    return rb_require_string(rb_file_absolute_path(fname, base));
}

IO.select(read_ios, write_ios = [], error_ios = [], timeout = nil) ⇒ Array?

Invokes system call select(2), which monitors multiple file descriptors, waiting until one or more of the file descriptors becomes ready for some class of I/O operation.

Not implemented on all platforms.

Each of the arguments read_ios, write_ios, and error_ios is an array of ::IO objects.

Argument timeout is an integer timeout interval in seconds.

The method monitors the IO objects given in all three arrays, waiting for some to be ready; returns a 3-element array whose elements are:

  • An array of the objects in read_ios that are ready for reading.

  • An array of the objects in write_ios that are ready for writing.

  • An array of the objects in error_ios have pending exceptions.

If no object becomes ready within the given timeout, nil is returned.

IO.select peeks the buffer of IO objects for testing readability. If the IO buffer is not empty, IO.select immediately notifies readability. This “peek” only happens for IO objects. It does not happen for IO-like objects such as OpenSSL::SSL::SSLSocket.

The best way to use IO.select is invoking it after non-blocking methods such as #read_nonblock, #write_nonblock, etc. The methods raise an exception which is extended by ::IO::WaitReadable or ::IO::WaitWritable. The modules notify how the caller should wait with IO.select. If ::IO::WaitReadable is raised, the caller should wait for reading. If ::IO::WaitWritable is raised, the caller should wait for writing.

So, blocking read (#readpartial) can be emulated using #read_nonblock and IO.select as follows:

begin
  result = io_like.read_nonblock(maxlen)
rescue IO::WaitReadable
  IO.select([io_like])
  retry
rescue IO::WaitWritable
  IO.select(nil, [io_like])
  retry
end

Especially, the combination of non-blocking methods and IO.select is preferred for ::IO like objects such as OpenSSL::SSL::SSLSocket. It has #to_io method to return underlying ::IO object. IO.select calls #to_io to obtain the file descriptor to wait.

This means that readability notified by IO.select doesn’t mean readability from OpenSSL::SSL::SSLSocket object.

The most likely situation is that OpenSSL::SSL::SSLSocket buffers some data. IO.select doesn’t see the buffer. So IO.select can block when OpenSSL::SSL::SSLSocket#readpartial doesn’t block.

However, several more complicated situations exist.

SSL is a protocol which is sequence of records. The record consists of multiple bytes. So, the remote side of SSL sends a partial record, IO.select notifies readability but OpenSSL::SSL::SSLSocket cannot decrypt a byte and OpenSSL::SSL::SSLSocket#readpartial will block.

Also, the remote side can request SSL renegotiation which forces the local SSL engine to write some data. This means OpenSSL::SSL::SSLSocket#readpartial may invoke #write system call and it can block. In such a situation, OpenSSL::SSL::SSLSocket#read_nonblock raises ::IO::WaitWritable instead of blocking. So, the caller should wait for ready for writability as above example.

The combination of non-blocking methods and IO.select is also useful for streams such as tty, pipe socket socket when multiple processes read from a stream.

Finally, Linux kernel developers don’t guarantee that readability of select(2) means readability of following read(2) even for a single process; see select(2)

Invoking IO.select before IO#readpartial works well as usual. However it is not the best way to use IO.select.

The writability notified by select(2) doesn’t show how many bytes are writable. IO#write method blocks until given whole string is written. So, IO#write(two or more bytes) can block after writability is notified by IO.select. IO#write_nonblock is required to avoid the blocking.

Blocking write (#write) can be emulated using #write_nonblock and IO.select as follows: ::IO::WaitReadable should also be rescued for SSL renegotiation in OpenSSL::SSL::SSLSocket.

while 0 < string.bytesize
  begin
    written = io_like.write_nonblock(string)
  rescue IO::WaitReadable
    IO.select([io_like])
    retry
  rescue IO::WaitWritable
    IO.select(nil, [io_like])
    retry
  end
  string = string.byteslice(written..-1)
end

Example:

rp, wp = IO.pipe
mesg = "ping "
100.times {
  # IO.select follows IO#read.  Not the best way to use IO.select.
  rs, ws, = IO.select([rp], [wp])
  if r = rs[0]
    ret = r.read(5)
    print ret
    case ret
    when /ping/
      mesg = "pong\n"
    when /pong/
      mesg = "ping "
    end
  end
  if w = ws[0]
    w.write(mesg)
  end
}

Output:

ping pong
ping pong
ping pong
(snipped)
ping
[ GitHub ]

  
# File 'io.c', line 10646

static VALUE
rb_f_select(int argc, VALUE *argv, VALUE obj)
{
    VALUE timeout;
    struct select_args args;
    struct timeval timerec;
    int i;

    rb_scan_args(argc, argv, "13", &args.read, &args.write, &args.except, &timeout);
    if (NIL_P(timeout)) {
	args.timeout = 0;
    }
    else {
	timerec = rb_time_interval(timeout);
	args.timeout = &timerec;
    }

    for (i = 0; i < numberof(args.fdsets); ++i)
	rb_fd_init(&args.fdsets[i]);

    return rb_ensure(select_call, (VALUE)&args, select_end, (VALUE)&args);
}

set_trace_func(proc) ⇒ Proc set_trace_func(nil) ⇒ nil

Establishes proc as the handler for tracing, or disables

tracing if the parameter is nil.

*Note:* this method is obsolete, please use TracePoint instead.

_proc_ takes up to six parameters:

*   an event name
*   a filename
*   a line number
*   an object id
*   a binding
*   the name of a class

_proc_ is invoked whenever an event occurs.

Events are:

c-call:: call a C-language routine
c-return:: return from a C-language routine
call:: call a Ruby method
class:: start a class or module definition
end:: finish a class or module definition
line:: execute code on a new line
raise:: raise an exception
return:: return from a Ruby method

Tracing is disabled within the context of _proc_.

    class Test
    def test
      a = 1
      b = 2
    end
    end

    set_trace_func proc { |event, file, line, id, binding, classname|
       printf "%8s %s:%-2d %10s %8s\n", event, file, line, id, classname
    }
    t = Test.new
    t.test

      line prog.rb:11               false
    c-call prog.rb:11        new    Class
    c-call prog.rb:11 initialize   Object
  c-return prog.rb:11 initialize   Object
  c-return prog.rb:11        new    Class
      line prog.rb:12               false
      call prog.rb:2        test     Test
      line prog.rb:3        test     Test
      line prog.rb:4        test     Test
    return prog.rb:4        test     Test

Note that for c-call and c-return events, the binding returned is the binding of the nearest Ruby method calling the C method, since C methods themselves do not have bindings.

[ GitHub ]

  
# File 'vm_trace.c', line 558

static VALUE
set_trace_func(VALUE obj, VALUE trace)
{
    rb_remove_event_hook(call_trace_func);

    if (NIL_P(trace)) {
	return Qnil;
    }

    if (!rb_obj_is_proc(trace)) {
	rb_raise(rb_eTypeError, "trace_func needs to be Proc");
    }

    rb_add_event_hook(call_trace_func, RUBY_EVENT_ALL, trace);
    return trace;
}

sleep([duration]) ⇒ Integer

Suspends the current thread for duration seconds (which may be any number, including a .Float with fractional seconds). Returns the actual number of seconds slept (rounded), which may be less than that asked for if another thread calls Thread#run. Called without an argument, sleep() will sleep forever.

Time.new    #=> 2008-03-08 19:56:19 +0900
sleep 1.2   #=> 1
Time.new    #=> 2008-03-08 19:56:20 +0900
sleep 1.9   #=> 2
Time.new    #=> 2008-03-08 19:56:22 +0900
[ GitHub ]

  
# File 'process.c', line 5163

static VALUE
rb_f_sleep(int argc, VALUE *argv, VALUE _)
{
    time_t beg = time(0);
    VALUE scheduler = rb_fiber_scheduler_current();

    if (scheduler != Qnil) {
        rb_fiber_scheduler_kernel_sleepv(scheduler, argc, argv);
    }
    else {
        if (argc == 0) {
            rb_thread_sleep_forever();
        }
        else {
            rb_check_arity(argc, 0, 1);
            rb_thread_wait_for(rb_time_interval(argv[0]));
        }
    }

    time_t end = time(0) - beg;

    return TIMET2NUM(end);
}

spawn([env,] command... [,options]) ⇒ pid Process.spawn([env,] command... [,options]) ⇒ pid

spawn executes specified command and return its pid.

pid = spawn("tar xf ruby-2.0.0-p195.tar.bz2")
Process.wait pid

pid = spawn(RbConfig.ruby, "-eputs'Hello, world!'")
Process.wait pid

This method is similar to .system but it doesn’t wait for the command to finish.

The parent process should use Process.wait to collect the termination status of its child or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.

spawn has bunch of options to specify process attributes:

env: hash
  name => val : set the environment variable
  name => nil : unset the environment variable

  the keys and the values except for nil must be strings.
command...:
  commandline                 : command line string which is passed to the standard shell
  cmdname, arg1, ...          : command name and one or more arguments (This form does not use the shell. See below for caveats.)
  [cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
options: hash
  clearing environment variables:
    :unsetenv_others => true   : clear environment variables except specified by env
    :unsetenv_others => false  : don't clear (default)
  process group:
    :pgroup => true or 0 : make a new process group
    :pgroup => pgid      : join the specified process group
    :pgroup => nil       : don't change the process group (default)
  create new process group: Windows only
    :new_pgroup => true  : the new process is the root process of a new process group
    :new_pgroup => false : don't create a new process group (default)
  resource limit: resourcename is core, cpu, data, etc.  See Process.setrlimit.
    :rlimit_resourcename => limit
    :rlimit_resourcename => [cur_limit, max_limit]
  umask:
    :umask => int
  redirection:
    key:
      FD              : single file descriptor in child process
      [FD, FD, ...]   : multiple file descriptor in child process
    value:
      FD                        : redirect to the file descriptor in parent process
      string                    : redirect to file with open(string, "r" or "w")
      [string]                  : redirect to file with open(string, File::RDONLY)
      [string, open_mode]       : redirect to file with open(string, open_mode, 0644)
      [string, open_mode, perm] : redirect to file with open(string, open_mode, perm)
      [:child, FD]              : redirect to the redirected file descriptor
      :close                    : close the file descriptor in child process
    FD is one of follows
      :in     : the file descriptor 0 which is the standard input
      :out    : the file descriptor 1 which is the standard output
      :err    : the file descriptor 2 which is the standard error
      integer : the file descriptor of specified the integer
      io      : the file descriptor specified as io.fileno
  file descriptor inheritance: close non-redirected non-standard fds (3, 4, 5, ...) or not
    :close_others => false  : inherit
  current directory:
    :chdir => str

The cmdname, arg1, ... form does not use the shell. However, on different OSes, different things are provided as built-in commands. An example of this is ‘echo’, which is a built-in on Windows, but is a normal program on Linux and Mac OS X. This means that Process.spawn 'echo', '%Path%' will display the contents of the %Path% environment variable on Windows, but Process.spawn 'echo', '$PATH' prints the literal $PATH.

If a hash is given as env, the environment is updated by env before exec(2) in the child process. If a pair in env has nil as the value, the variable is deleted.

# set FOO as BAR and unset BAZ.
pid = spawn({"FOO"=>"BAR", "BAZ"=>nil}, command)

If a hash is given as options, it specifies process group, create new process group, resource limit, current directory, umask and redirects for the child process. Also, it can be specified to clear environment variables.

The :unsetenv_others key in options specifies to clear environment variables, other than specified by env.

pid = spawn(command, :unsetenv_others=>true) # no environment variable
pid = spawn({"FOO"=>"BAR"}, command, :unsetenv_others=>true) # FOO only

The :pgroup key in options specifies a process group. The corresponding value should be true, zero, a positive integer, or nil. true and zero cause the process to be a process leader of a new process group. A non-zero positive integer causes the process to join the provided process group. The default value, nil, causes the process to remain in the same process group.

pid = spawn(command, :pgroup=>true) # process leader
pid = spawn(command, :pgroup=>10) # belongs to the process group 10

The :new_pgroup key in options specifies to pass CREATE_NEW_PROCESS_GROUP flag to CreateProcessW() that is Windows API. This option is only for Windows. true means the new process is the root process of the new process group. The new process has CTRL+C disabled. This flag is necessary for Process.kill(:SIGINT, pid) on the subprocess. :new_pgroup is false by default.

pid = spawn(command, :new_pgroup=>true)  # new process group
pid = spawn(command, :new_pgroup=>false) # same process group

The :rlimit_foo key specifies a resource limit. foo should be one of resource types such as core. The corresponding value should be an integer or an array which have one or two integers: same as cur_limit and max_limit arguments for Process.setrlimit.

cur, max = Process.getrlimit(:CORE)
pid = spawn(command, :rlimit_core=>[0,max]) # disable core temporary.
pid = spawn(command, :rlimit_core=>max) # enable core dump
pid = spawn(command, :rlimit_core=>0) # never dump core.

The :umask key in options specifies the umask.

pid = spawn(command, :umask=>077)

The :in, :out, :err, an integer, an ::IO and an array key specifies a redirection. The redirection maps a file descriptor in the child process.

For example, stderr can be merged into stdout as follows:

pid = spawn(command, :err=>:out)
pid = spawn(command, 2=>1)
pid = spawn(command, STDERR=>:out)
pid = spawn(command, STDERR=>STDOUT)

The hash keys specifies a file descriptor in the child process started by #spawn. :err, 2 and STDERR specifies the standard error stream (stderr).

The hash values specifies a file descriptor in the parent process which invokes #spawn. :out, 1 and STDOUT specifies the standard output stream (stdout).

In the above example, the standard output in the child process is not specified. So it is inherited from the parent process.

The standard input stream (stdin) can be specified by :in, 0 and STDIN.

A filename can be specified as a hash value.

pid = spawn(command, :in=>"/dev/null") # read mode
pid = spawn(command, :out=>"/dev/null") # write mode
pid = spawn(command, :err=>"log") # write mode
pid = spawn(command, [:out, :err]=>"/dev/null") # write mode
pid = spawn(command, 3=>"/dev/null") # read mode

For stdout and stderr (and combination of them), it is opened in write mode. Otherwise read mode is used.

For specifying flags and permission of file creation explicitly, an array is used instead.

pid = spawn(command, :in=>["file"]) # read mode is assumed
pid = spawn(command, :in=>["file", "r"])
pid = spawn(command, :out=>["log", "w"]) # 0644 assumed
pid = spawn(command, :out=>["log", "w", 0600])
pid = spawn(command, :out=>["log", File::WRONLY|File::EXCL|File::CREAT, 0600])

The array specifies a filename, flags and permission. The flags can be a string or an integer. If the flags is omitted or nil, File::RDONLY is assumed. The permission should be an integer. If the permission is omitted or nil, 0644 is assumed.

If an array of IOs and integers are specified as a hash key, all the elements are redirected.

# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, [:out, :err]=>["log", "w"])

Another way to merge multiple file descriptors is [:child, fd]. [:child, fd] means the file descriptor in the child process. This is different from fd. For example, :err=>:out means redirecting child stderr to parent stdout. But :err=>[:child, :out] means redirecting child stderr to child stdout. They differ if stdout is redirected in the child process as follows.

# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, :out=>["log", "w"], :err=>[:child, :out])

[:child, :out] can be used to merge stderr into stdout in IO.popen. In this case, IO.popen redirects stdout to a pipe in the child process and [:child, :out] refers the redirected stdout.

io = IO.popen(["sh", "-c", "echo out; echo err >&2", :err=>[:child, :out]])
p io.read #=> "out\nerr\n"

The :chdir key in options specifies the current directory.

pid = spawn(command, :chdir=>"/var/tmp")

spawn closes all non-standard unspecified descriptors by default. The “standard” descriptors are 0, 1 and 2. This behavior is specified by :close_others option. :close_others doesn’t affect the standard descriptors which are closed only if :close is specified explicitly.

pid = spawn(command, :close_others=>true)  # close 3,4,5,... (default)
pid = spawn(command, :close_others=>false) # don't close 3,4,5,...

:close_others is false by default for spawn and IO.popen.

Note that fds which close-on-exec flag is already set are closed regardless of :close_others option.

So IO.pipe and spawn can be used as IO.popen.

# similar to r = IO.popen(command)
r, w = IO.pipe
pid = spawn(command, :out=>w)   # r, w is closed in the child process.
w.close

:close is specified as a hash value to close a fd individually.

f = open(foo)
system(command, f=>:close)        # don't inherit f.

If a file descriptor need to be inherited, io=>io can be used.

# valgrind has --log-fd option for log destination.
# log_w=>log_w indicates log_w.fileno inherits to child process.
log_r, log_w = IO.pipe
pid = spawn("valgrind", "--log-fd=#{log_w.fileno}", "echo", "a", log_w=>log_w)
log_w.close
p log_r.read

It is also possible to exchange file descriptors.

pid = spawn(command, :out=>:err, :err=>:out)

The hash keys specify file descriptors in the child process. The hash values specifies file descriptors in the parent process. So the above specifies exchanging stdout and stderr. Internally, spawn uses an extra file descriptor to resolve such cyclic file descriptor mapping.

See .exec for the standard shell.

[ GitHub ]

  
# File 'process.c', line 5119

static VALUE
rb_f_spawn(int argc, VALUE *argv, VALUE _)
{
    rb_pid_t pid;
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };
    VALUE execarg_obj, fail_str;
    struct rb_execarg *eargp;

    execarg_obj = rb_execarg_new(argc, argv, TRUE, FALSE);
    eargp = rb_execarg_get(execarg_obj);
    fail_str = eargp->use_shell ? eargp->invoke.sh.shell_script : eargp->invoke.cmd.command_name;

    pid = rb_execarg_spawn(execarg_obj, errmsg, sizeof(errmsg));

    if (pid == -1) {
	int err = errno;
	rb_exec_fail(eargp, err, errmsg);
	RB_GC_GUARD(execarg_obj);
	rb_syserr_fail_str(err, fail_str);
    }
#if defined(HAVE_WORKING_FORK) || defined(HAVE_SPAWNV)
    return PIDT2NUM(pid);
#else
    return Qnil;
#endif
}

format(format_string *objects) ⇒ String sprintf(format_string *objects) ⇒ String

Alias for .format.

srand(number = Random.new_seed) ⇒ old_seed

Seeds the system pseudo-random number generator, with number. The previous seed value is returned.

If number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.

srand may be used to ensure repeatable sequences of pseudo-random numbers between different runs of the program. By setting the seed to a known value, programs can be made deterministic during testing.

srand 1234               # => 268519324636777531569100071560086917274
[ rand, rand ]           # => [0.1915194503788923, 0.6221087710398319]
[ rand(10), rand(1000) ] # => [4, 664]
srand 1234               # => 1234
[ rand, rand ]           # => [0.1915194503788923, 0.6221087710398319]
[ GitHub ]

  
# File 'random.c', line 926

static VALUE
rb_f_srand(int argc, VALUE *argv, VALUE obj)
{
    VALUE seed, old;
    rb_random_mt_t *r = rand_mt_start(default_rand());

    if (rb_check_arity(argc, 0, 1) == 0) {
        seed = random_seed(obj);
    }
    else {
	seed = rb_to_int(argv[0]);
    }
    old = r->base.seed;
    rand_init(&random_mt_if, &r->base, seed);
    r->base.seed = seed;

    return old;
}

String(object) ⇒ Object, String

Returns a string converted from object.

Tries to convert object to a string using to_str first and to_s second:

String([0, 1, 2])        # => "[0, 1, 2]"
String(0..5)             # => "0..5"
String({foo: 0, bar: 1}) # => "{:foo=>0, :bar=>1}"

Raises ::TypeError if object cannot be converted to a string.

[ GitHub ]

  
# File 'object.c', line 3705

static VALUE
rb_f_string(VALUE obj, VALUE arg)
{
    return rb_String(arg);
}

sub(pattern, replacement) ⇒ $_ sub(pattern) {|...| ... } ⇒ $_

Equivalent to $_.sub(args), except that $_ will be updated if substitution occurs. Available only when -p/-n command line option specified.

[ GitHub ]

  
# File 'ruby.c', line 1608

static VALUE
rb_f_sub(int argc, VALUE *argv, VALUE _)
{
    VALUE str = rb_funcall_passing_block(uscore_get(), rb_intern("sub"), argc, argv);
    rb_lastline_set(str);
    return str;
}

syscall(integer_callno, *arguments) ⇒ Integer

Invokes Posix system call syscall(2), which calls a specified function.

Calls the operating system function identified by integer_callno; returns the result of the function or raises ::SystemCallError if it failed. The effect of the call is platform-dependent. The arguments and returned value are platform-dependent.

For each of arguments: if it is an integer, it is passed directly; if it is a string, it is interpreted as a binary sequence of bytes. There may be as many as nine such arguments.

Arguments integer_callno and argument, as well as the returned value, are platform-dependent.

Note: ::Method syscall is essentially unsafe and unportable. The DL (Fiddle) library is preferred for safer and a bit more portable programming.

Not implemented on all platforms.

[ GitHub ]

  
# File 'io.c', line 11114

static VALUE
rb_f_syscall(int argc, VALUE *argv, VALUE _)
{
    VALUE arg[8];
#if SIZEOF_VOIDP == 8 && defined(HAVE___SYSCALL) && SIZEOF_INT != 8 /* mainly *BSD */
# define SYSCALL __syscall
# define NUM2SYSCALLID(x) NUM2LONG(x)
# define RETVAL2NUM(x) LONG2NUM(x)
# if SIZEOF_LONG == 8
    long num, retval = -1;
# elif SIZEOF_LONG_LONG == 8
    long long num, retval = -1;
# else
#  error ---->> it is asserted that __syscall takes the first argument and returns retval in 64bit signed integer. <<----
# endif
#elif defined(__linux__)
# define SYSCALL syscall
# define NUM2SYSCALLID(x) NUM2LONG(x)
# define RETVAL2NUM(x) LONG2NUM(x)
    /*
     * Linux man page says, syscall(2) function prototype is below.
     *
     *     int syscall(int number, ...);
     *
     * But, it's incorrect. Actual one takes and returned long. (see unistd.h)
     */
    long num, retval = -1;
#else
# define SYSCALL syscall
# define NUM2SYSCALLID(x) NUM2INT(x)
# define RETVAL2NUM(x) INT2NUM(x)
    int num, retval = -1;
#endif
    int i;

    if (RTEST(ruby_verbose)) {
        rb_category_warning(RB_WARN_CATEGORY_DEPRECATED,
            "We plan to remove a syscall function at future release. DL(Fiddle) provides safer alternative.");
    }

    if (argc == 0)
	rb_raise(rb_eArgError, "too few arguments for syscall");
    if (argc > numberof(arg))
	rb_raise(rb_eArgError, "too many arguments for syscall");
    num = NUM2SYSCALLID(argv[0]); ++argv;
    for (i = argc - 1; i--; ) {
	VALUE v = rb_check_string_type(argv[i]);

	if (!NIL_P(v)) {
	    SafeStringValue(v);
	    rb_str_modify(v);
	    arg[i] = (VALUE)StringValueCStr(v);
	}
	else {
	    arg[i] = (VALUE)NUM2LONG(argv[i]);
	}
    }

    switch (argc) {
      case 1:
	retval = SYSCALL(num);
	break;
      case 2:
	retval = SYSCALL(num, arg[0]);
	break;
      case 3:
	retval = SYSCALL(num, arg[0],arg[1]);
	break;
      case 4:
	retval = SYSCALL(num, arg[0],arg[1],arg[2]);
	break;
      case 5:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3]);
	break;
      case 6:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4]);
	break;
      case 7:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5]);
	break;
      case 8:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6]);
	break;
    }

    if (retval == -1)
	rb_sys_fail(0);
    return RETVAL2NUM(retval);
#undef SYSCALL
#undef NUM2SYSCALLID
#undef RETVAL2NUM
}

system([env,] command... [,options], exception: false) ⇒ true, ...

Executes command… in a subshell. command… is one of following forms.

This method has potential security vulnerabilities if called with untrusted input; see Command Injection.

commandline

command line string which is passed to the standard shell

cmdname, arg1, ...

command name and one or more arguments (no shell)

[cmdname, argv0], arg1, ...

command name, argv[0] and zero or more arguments (no shell)

system returns true if the command gives zero exit status, false for non zero exit status. Returns nil if command execution fails. An error status is available in $?.

If the exception: true argument is passed, the method raises an exception instead of returning false or nil.

The arguments are processed in the same way as for .spawn.

The hash arguments, env and options, are same as #exec and #spawn. See .spawn for details.

system("echo *")
system("echo", "*")

produces:

config.h main.rb
*

Error handling:

system("cat nonexistent.txt")
# => false
system("catt nonexistent.txt")
# => nil

system("cat nonexistent.txt", exception: true)
# RuntimeError (Command failed with exit 1: cat)
system("catt nonexistent.txt", exception: true)
# Errno::ENOENT (No such file or directory - catt)

See .exec for the standard shell.

[ GitHub ]

  
# File 'process.c', line 4788

static VALUE
rb_f_system(int argc, VALUE *argv, VALUE _)
{
    VALUE execarg_obj = rb_execarg_new(argc, argv, TRUE, TRUE);
    struct rb_execarg *eargp = rb_execarg_get(execarg_obj);

    struct rb_process_status status = {0};
    eargp->status = &status;

    rb_last_status_clear();

    // This function can set the thread's last status.
    // May be different from waitpid_state.pid on exec failure.
    rb_pid_t pid = rb_execarg_spawn(execarg_obj, 0, 0);

    if (pid > 0) {
        VALUE status = rb_process_status_wait(pid, 0);
        struct rb_process_status *data = RTYPEDDATA_DATA(status);

        // Set the last status:
        rb_obj_freeze(status);
        GET_THREAD()->last_status = status;

        if (data->status == EXIT_SUCCESS) {
            return Qtrue;
        }

        if (data->error != 0) {
            if (eargp->exception) {
                VALUE command = eargp->invoke.sh.shell_script;
                RB_GC_GUARD(execarg_obj);
                rb_syserr_fail_str(data->error, command);
            }
            else {
                return Qnil;
            }
        }
        else if (eargp->exception) {
            VALUE command = eargp->invoke.sh.shell_script;
            VALUE str = rb_str_new_cstr("Command failed with");
            rb_str_cat_cstr(pst_message_status(str, data->status), ": ");
            rb_str_append(str, command);
            RB_GC_GUARD(execarg_obj);
            rb_exc_raise(rb_exc_new_str(rb_eRuntimeError, str));
        }
        else {
            return Qfalse;
        }

        RB_GC_GUARD(status);
    }

    if (eargp->exception) {
        VALUE command = eargp->invoke.sh.shell_script;
        RB_GC_GUARD(execarg_obj);
        rb_syserr_fail_str(errno, command);
    }
    else {
        return Qnil;
    }
}

test(cmd, file1 [, file2] ) ⇒ Object

Uses the character cmd to perform various tests on file1 (first table below) or on file1 and file2 (second table).

::File tests on a single file:

Cmd    Returns   Meaning
"A"  | Time    | Last access time for file1
"b"  | boolean | True if file1 is a block device
"c"  | boolean | True if file1 is a character device
"C"  | Time    | Last change time for file1
"d"  | boolean | True if file1 exists and is a directory
"e"  | boolean | True if file1 exists
"f"  | boolean | True if file1 exists and is a regular file
"g"  | boolean | True if file1 has the \CF{setgid} bit
     |         | set (false under NT)
"G"  | boolean | True if file1 exists and has a group
     |         | ownership equal to the caller's group
"k"  | boolean | True if file1 exists and has the sticky bit set
"l"  | boolean | True if file1 exists and is a symbolic link
"M"  | Time    | Last modification time for file1
"o"  | boolean | True if file1 exists and is owned by
     |         | the caller's effective uid
"O"  | boolean | True if file1 exists and is owned by
     |         | the caller's real uid
"p"  | boolean | True if file1 exists and is a fifo
"r"  | boolean | True if file1 is readable by the effective
     |         | uid/gid of the caller
"R"  | boolean | True if file is readable by the real
     |         | uid/gid of the caller
"s"  | int/nil | If file1 has nonzero size, return the size,
     |         | otherwise return nil
"S"  | boolean | True if file1 exists and is a socket
"u"  | boolean | True if file1 has the setuid bit set
"w"  | boolean | True if file1 exists and is writable by
     |         | the effective uid/gid
"W"  | boolean | True if file1 exists and is writable by
     |         | the real uid/gid
"x"  | boolean | True if file1 exists and is executable by
     |         | the effective uid/gid
"X"  | boolean | True if file1 exists and is executable by
     |         | the real uid/gid
"z"  | boolean | True if file1 exists and has a zero length

Tests that take two files:

"-"  | boolean | True if file1 and file2 are identical
"="  | boolean | True if the modification times of file1
     |         | and file2 are equal
"<"  | boolean | True if the modification time of file1
     |         | is prior to that of file2
">"  | boolean | True if the modification time of file1
     |         | is after that of file2
[ GitHub ]

  
# File 'file.c', line 5419

static VALUE
rb_f_test(int argc, VALUE *argv, VALUE _)
{
    int cmd;

    if (argc == 0) rb_check_arity(argc, 2, 3);
    cmd = NUM2CHR(argv[0]);
    if (cmd == 0) {
        goto unknown;
    }
    if (strchr("bcdefgGkloOprRsSuwWxXz", cmd)) {
	CHECK(1);
	switch (cmd) {
	  case 'b':
	    return rb_file_blockdev_p(0, argv[1]);

	  case 'c':
	    return rb_file_chardev_p(0, argv[1]);

	  case 'd':
	    return rb_file_directory_p(0, argv[1]);

	  case 'e':
	    return rb_file_exist_p(0, argv[1]);

	  case 'f':
	    return rb_file_file_p(0, argv[1]);

	  case 'g':
	    return rb_file_sgid_p(0, argv[1]);

	  case 'G':
	    return rb_file_grpowned_p(0, argv[1]);

	  case 'k':
	    return rb_file_sticky_p(0, argv[1]);

	  case 'l':
	    return rb_file_symlink_p(0, argv[1]);

	  case 'o':
	    return rb_file_owned_p(0, argv[1]);

	  case 'O':
	    return rb_file_rowned_p(0, argv[1]);

	  case 'p':
	    return rb_file_pipe_p(0, argv[1]);

	  case 'r':
	    return rb_file_readable_p(0, argv[1]);

	  case 'R':
	    return rb_file_readable_real_p(0, argv[1]);

	  case 's':
	    return rb_file_size_p(0, argv[1]);

	  case 'S':
	    return rb_file_socket_p(0, argv[1]);

	  case 'u':
	    return rb_file_suid_p(0, argv[1]);

	  case 'w':
	    return rb_file_writable_p(0, argv[1]);

	  case 'W':
	    return rb_file_writable_real_p(0, argv[1]);

	  case 'x':
	    return rb_file_executable_p(0, argv[1]);

	  case 'X':
	    return rb_file_executable_real_p(0, argv[1]);

	  case 'z':
	    return rb_file_zero_p(0, argv[1]);
	}
    }

    if (strchr("MAC", cmd)) {
	struct stat st;
	VALUE fname = argv[1];

	CHECK(1);
	if (rb_stat(fname, &st) == -1) {
	    int e = errno;
	    FilePathValue(fname);
	    rb_syserr_fail_path(e, fname);
	}

	switch (cmd) {
	  case 'A':
	    return stat_atime(&st);
	  case 'M':
	    return stat_mtime(&st);
	  case 'C':
	    return stat_ctime(&st);
	}
    }

    if (cmd == '-') {
	CHECK(2);
	return rb_file_identical_p(0, argv[1], argv[2]);
    }

    if (strchr("=<>", cmd)) {
	struct stat st1, st2;
        struct timespec t1, t2;

	CHECK(2);
	if (rb_stat(argv[1], &st1) < 0) return Qfalse;
	if (rb_stat(argv[2], &st2) < 0) return Qfalse;

        t1 = stat_mtimespec(&st1);
        t2 = stat_mtimespec(&st2);

	switch (cmd) {
	  case '=':
	    if (t1.tv_sec == t2.tv_sec && t1.tv_nsec == t2.tv_nsec) return Qtrue;
	    return Qfalse;

	  case '>':
	    if (t1.tv_sec > t2.tv_sec) return Qtrue;
	    if (t1.tv_sec == t2.tv_sec && t1.tv_nsec > t2.tv_nsec) return Qtrue;
	    return Qfalse;

	  case '<':
	    if (t1.tv_sec < t2.tv_sec) return Qtrue;
	    if (t1.tv_sec == t2.tv_sec && t1.tv_nsec < t2.tv_nsec) return Qtrue;
	    return Qfalse;
	}
    }
  unknown:
    /* unknown command */
    if (ISPRINT(cmd)) {
        rb_raise(rb_eArgError, "unknown command '%s%c'", cmd == '\'' || cmd == '\\' ? "\\" : "", cmd);
    }
    else {
        rb_raise(rb_eArgError, "unknown command \"\\x%02X\"", cmd);
    }
    UNREACHABLE_RETURN(Qundef);
}

throw(tag [, obj])

Transfers control to the end of the active .catch block waiting for tag. Raises ::UncaughtThrowError if there is no .catch block for the tag. The optional second parameter supplies a return value for the .catch block, which otherwise defaults to nil. For examples, see .catch.

[ GitHub ]

  
# File 'vm_eval.c', line 2253

static VALUE
rb_f_throw(int argc, VALUE *argv, VALUE _)
{
    VALUE tag, value;

    rb_scan_args(argc, argv, "11", &tag, &value);
    rb_throw_obj(tag, value);
    UNREACHABLE_RETURN(Qnil);
}

trace_var(symbol, cmd) ⇒ nil trace_var(symbol) {|val| ... } ⇒ nil

Controls tracing of assignments to global variables. The parameter symbol identifies the variable (as either a string name or a symbol identifier). cmd (which may be a string or a ::Proc object) or block is executed whenever the variable is assigned. The block or ::Proc object receives the variable’s new value as a parameter. Also see .untrace_var.

trace_var :$_, proc {|v| puts "$_ is now '#{v}'" }
$_ = "hello"
$_ = ' there'

produces:

$_ is now 'hello'
$_ is now ' there'
[ GitHub ]

  
# File 'eval.c', line 1998

static VALUE
f_trace_var(int c, const VALUE *a, VALUE _)
{
    return rb_f_trace_var(c, a);
}

Signal.trap(signal, command) ⇒ Object Signal.trap(signal) {|| ... } ⇒ Object

Specifies the handling of signals. The first parameter is a signal name (a string such as “SIGALRM”, “SIGUSR1”, and so on) or a signal number. The characters “SIG” may be omitted from the signal name. The command or block specifies code to be run when the signal is raised. If the command is the string “IGNORE” or “SIG_IGN”, the signal will be ignored. If the command is “DEFAULT” or “SIG_DFL”, the Ruby’s default handler will be invoked. If the command is “EXIT”, the script will be terminated by the signal. If the command is “SYSTEM_DEFAULT”, the operating system’s default handler will be invoked. Otherwise, the given command or block will be run. The special signal name “EXIT” or signal number zero will be invoked just prior to program termination. trap returns the previous handler for the given signal.

Signal.trap(0, proc { puts "Terminating: #{$$}" })
Signal.trap("CLD")  { puts "Child died" }
fork && Process.wait

produces:

Terminating: 27461
Child died
Terminating: 27460
[ GitHub ]

  
# File 'signal.c', line 1391

static VALUE
sig_trap(int argc, VALUE *argv, VALUE _)
{
    int sig;
    sighandler_t func;
    VALUE cmd;

    rb_check_arity(argc, 1, 2);

    sig = trap_signm(argv[0]);
    if (reserved_signal_p(sig)) {
        const char *name = signo2signm(sig);
        if (name)
            rb_raise(rb_eArgError, "can't trap reserved signal: SIG%s", name);
        else
            rb_raise(rb_eArgError, "can't trap reserved signal: %d", sig);
    }

    if (argc == 1) {
	cmd = rb_block_proc();
	func = sighandler;
    }
    else {
	cmd = argv[1];
	func = trap_handler(&cmd, sig);
    }

    if (rb_obj_is_proc(cmd) &&
        !rb_ractor_main_p() && !rb_ractor_shareable_p(cmd)) {
        cmd = rb_proc_isolate(cmd);
    }

    return trap(sig, func, cmd);
}

untrace_var(symbol [, cmd] ) ⇒ Array?

Removes tracing for the specified command on the given global variable and returns nil. If no command is specified, removes all tracing for that variable and returns an array containing the commands actually removed.

[ GitHub ]

  
# File 'eval.c', line 2014

static VALUE
f_untrace_var(int c, const VALUE *a, VALUE _)
{
    return rb_f_untrace_var(c, a);
}

warn(*msgs, uplevel: nil, category: nil) ⇒ nil (mod_func)

If warnings have been disabled (for example with the -W0 flag), does nothing. Otherwise, converts each of the messages to strings, appends a newline character to the string if the string does not end in a newline, and calls Warning#warn with the string.

  warn("warning 1", "warning 2")

<em>produces:</em>

  warning 1
  warning 2

If the uplevel keyword argument is given, the string will be prepended with information for the given caller frame in the same format used by the rb_warn C function.

  # In baz.rb
  def foo
    warn("invalid call to foo", uplevel: 1)
  end

  def bar
    foo
  end

  bar

<em>produces:</em>

  baz.rb:6: warning: invalid call to foo

If category keyword argument is given, passes the category to Warning#warn. The category given must be be one of the following categories:

:deprecated

Used for warning for deprecated functionality that may

be removed in the future.
:experimental

Used for experimental features that may change in

future releases.
[ GitHub ]

  
# File 'warning.rb', line 50

def warn(*msgs, uplevel: nil, category: nil)
  Primitive.rb_warn_m(msgs, uplevel, category)
end

Instance Attribute Details

frozen?Boolean (readonly)

Returns the freeze status of obj.

a = [ "a", "b", "c" ]
a.freeze    #=> ["a", "b", "c"]
a.frozen?   #=> true
[ GitHub ]

  
# File 'kernel.rb', line 67

def frozen?
  Primitive.attr! 'inline'
  Primitive.cexpr! 'rb_obj_frozen_p(self)'
end

Instance Method Details

class ⇒ class

Returns the class of obj. This method must always be called with an explicit receiver, as #class is also a reserved word in Ruby.

1.class      #=> Integer
self.class   #=> Object
[ GitHub ]

  
# File 'kernel.rb', line 18

def class
  Primitive.attr! 'inline'
  Primitive.cexpr! 'rb_obj_class(self)'
end

clone(freeze: nil) ⇒ Object

Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. #clone copies the frozen value state of obj, unless the :freeze keyword argument is given with a false or true value. See also the discussion under Object#dup.

class Klass
   attr_accessor :str
end
s1 = Klass.new      #=> #<Klass:0x401b3a38>
s1.str = "Hello"    #=> "Hello"
s2 = s1.clone       #=> #<Klass:0x401b3998 @str="Hello">
s2.str[1,4] = "i"   #=> "i"
s1.inspect          #=> "#<Klass:0x401b3a38 @str=\"Hi\">"
s2.inspect          #=> "#<Klass:0x401b3998 @str=\"Hi\">"

This method may have class-specific behavior. If so, that behavior will be documented under the #initialize_copy method of the class.

[ GitHub ]

  
# File 'kernel.rb', line 47

def clone(freeze: nil)
  Primitive.rb_obj_clone2(freeze)
end

pp(*objs) (private) Also known as: #pp

Alias for pp.

[ GitHub ]

  
# File 'prelude.rb', line 19

def pp(*objs)
  require 'pp'
  pp(*objs)
end

tap {|x| ... } ⇒ Object

Yields self to the block, and then returns self. The primary purpose of this method is to “tap into” a method chain, in order to perform operations on intermediate results within the chain.

(1..10)                  .tap {|x| puts "original: #{x}" }
  .to_a                  .tap {|x| puts "array:    #{x}" }
  .select {|x| x.even? } .tap {|x| puts "evens:    #{x}" }
  .map {|x| x*x }        .tap {|x| puts "squares:  #{x}" }

Yields:

  • (_self)

Yield Parameters:

  • _self (Kernel)

    the object that the method was called on

[ GitHub ]

  
# File 'kernel.rb', line 89

def tap
  yield(self)
  self
end

then {|x| ... } ⇒ Object

Yields self to the block and returns the result of the block.

3.next.then {|x| x**x }.to_s             #=> "256"

Good usage for then is value piping in method chains:

require 'open-uri'
require 'json'

construct_url(arguments).
  then {|url| URI(url).read }.
  then {|response| JSON.parse(response) }

When called without block, the method returns ::Enumerator, which can be used, for example, for conditional circuit-breaking:

# meets condition, no-op
1.then.detect(&:odd?)            # => 1
# does not meet condition, drop value
2.then.detect(&:odd?)            # => nil

Yields:

  • (_self)

Yield Parameters:

  • _self (Kernel)

    the object that the method was called on

[ GitHub ]

  
# File 'kernel.rb', line 120

def then
  unless Primitive.block_given_p
    return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_obj_size)'
  end
  yield(self)
end

yield_self {|x| ... } ⇒ Object

Yields self to the block and returns the result of the block.

"my string".yield_self {|s| s.upcase }   #=> "MY STRING"

Good usage for #then is value piping in method chains:

require 'open-uri'
require 'json'

construct_url(arguments).
  then {|url| URI(url).read }.
  then {|response| JSON.parse(response) }

Yields:

  • (_self)

Yield Parameters:

  • _self (Kernel)

    the object that the method was called on

[ GitHub ]

  
# File 'kernel.rb', line 144

def yield_self
  unless Primitive.block_given_p
    return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_obj_size)'
  end
  yield(self)
end