Module: Kernel

Included in:
Object
Defined in:
object.c,
object.c

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"

Instance Method Summary (collapse)

Instance Method Details

- (Object) __callee__

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



1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
# File 'eval.c', line 1546

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

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

- (String) __dir__

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__)).

Returns:



1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
# File 'eval.c', line 1569

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

- (Object) __method__

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



1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
# File 'eval.c', line 1524

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

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

- (String) `

Returns the standard output of running cmd in a subshell. The built-in syntax %x{...} uses this method. Sets $? to the process status.

`date`                   #=> "Wed Apr  9 08:56:30 CDT 2003\n"
`ls testdir`.split[1]    #=> "main.rb"
`echo oops && exit 99`   #=> "oops\n"
$?.exitstatus            #=> 99

Returns:



8089
8090
8091
8092
8093
8094
8095
8096
8097
8098
8099
8100
8101
8102
8103
8104
8105
8106
# File 'io.c', line 8089

static VALUE
rb_f_backquote(VALUE obj, VALUE str)
{
    volatile 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);

    return result;
}

- (Object) abort - (Object) Kernel::abort([msg]) - (Object) Process::abort([msg])

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



3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
# File 'process.c', line 3673

VALUE
rb_f_abort(int argc, VALUE *argv)
{
    if (argc == 0) {
	if (!NIL_P(GET_THREAD()->errinfo)) {
	    ruby_error_print();
	}
	rb_exit(EXIT_FAILURE);
    }
    else {
	VALUE args[2];

	rb_scan_args(argc, argv, "1", &args[1]);
	StringValue(argv[0]);
	rb_io_puts(argc, argv, rb_stderr);
	args[0] = INT2NUM(EXIT_FAILURE);
	rb_exc_raise(rb_class_new_instance(2, args, rb_eSystemExit));
    }

    UNREACHABLE;
}

- (Array) Array(arg)

Returns arg as an Array.

First tries to call Array#to_ary on arg, then Array#to_a.

Array(1..5)   #=> [1, 2, 3, 4, 5]

Returns:



2868
2869
2870
2871
2872
# File 'object.c', line 2868

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

- (Proc) at_exit { ... }

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

Yields:

Returns:



37
38
39
40
41
42
43
44
45
46
47
48
# File 'eval_jump.c', line 37

static VALUE
rb_f_at_exit(void)
{
    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;
}

- (nil) autoload

Registers filename to be loaded (using Kernel::require) the first time that module (which may be a String or a symbol) is accessed.

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

Returns:

  • (nil)


1082
1083
1084
1085
1086
1087
1088
1089
1090
# File 'load.c', line 1082

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

- (String?) autoload?(name)

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

autoload(:B, "b")
autoload?(:B)            #=> "b"

Returns:

Returns:

  • (Boolean)


1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
# File 'load.c', line 1103

static VALUE
rb_f_autoload_p(VALUE obj, VALUE sym)
{
    /* 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(klass, sym);
}

- (Binding) binding

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)
  return binding
end
b = get_binding("hello")
eval("param", b)   #=> "hello"

Returns:



365
366
367
368
369
# File 'proc.c', line 365

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

- (Boolean) block_given? - (Boolean) iterator?

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"

Overloads:

  • - (Boolean) block_given?

    Returns:

    • (Boolean)
  • - (Boolean) iterator?

    Returns:

    • (Boolean)

Returns:

  • (Boolean)


1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
# File 'vm_eval.c', line 1922

VALUE
rb_f_block_given_p(void)
{
    rb_thread_t *th = GET_THREAD();
    rb_control_frame_t *cfp = th->cfp;
    cfp = vm_get_ruby_level_caller_cfp(th, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));

    if (cfp != 0 && VM_CF_BLOCK_PTR(cfp)) {
	return Qtrue;
    }
    else {
	return Qfalse;
    }
}

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

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

Overloads:

  • - (Array?) caller(start = 1, length = nil)

    Returns:

  • - (Array?) caller(range)

    Returns:



908
909
910
911
912
# File 'vm_backtrace.c', line 908

static VALUE
rb_f_caller(int argc, VALUE *argv)
{
    return vm_backtrace_to_ary(GET_THREAD(), argc, argv, 1, 1, 1);
}

- (Object) caller_locations(start = 1, length = nil) - (Object) caller_locations(range)

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.



936
937
938
939
940
# File 'vm_backtrace.c', line 936

static VALUE
rb_f_caller_locations(int argc, VALUE *argv)
{
    return vm_backtrace_to_ary(GET_THREAD(), argc, argv, 1, 1, 0);
}

- (Object) catch([arg]) {|tag| ... }

catch executes its block. If a throw is executed, Ruby searches up its stack for a catch block with a tag corresponding to the throw's tag. If found, that block is terminated, and catch returns the value given to throw. If throw is not called, the block terminates normally, and the value of catch is the value of the last expression evaluated. catch expressions may be nested, and the throw call need not be in lexical scope.

def routine(n)
  puts n
  throw :done if n <= 0
  routine(n-1)
end

catch(:done) { routine(3) }

produces:

3
2
1
0

when arg is given, catch yields it as is, or when no arg is given, catch assigns a new unique object to throw. this is useful for nested catch. arg can be an arbitrary object, not only Symbol.

Yields:

  • (tag)

Returns:



1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
# File 'vm_eval.c', line 1794

static VALUE
rb_f_catch(int argc, VALUE *argv)
{
    VALUE tag;

    if (argc == 0) {
	tag = rb_obj_alloc(rb_cObject);
    }
    else {
	rb_scan_args(argc, argv, "01", &tag);
    }
    return rb_catch_obj(tag, catch_i, 0);
}

- (Numeric) Complex(x[, y])

Returns x+i*y;

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

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.

Returns:



509
510
511
512
513
# File 'complex.c', line 509

static VALUE
nucomp_f_complex(int argc, VALUE *argv, VALUE klass)
{
    return rb_funcall2(rb_cComplex, id_convert, argc, argv);
}

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

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"

Returns:



1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
# File 'vm_eval.c', line 1332

VALUE
rb_f_eval(int argc, 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;
    return eval_string(self, src, scope, file, line);
}

- (Object) exec([env,][,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 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, same as ENV["RUBYSHELL"] (or ENV["COMSPEC"] on Windows NT series), and similar.

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

  • no meta characters

  • no shell reserved word and no 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 Kernel#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


2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
# File 'process.c', line 2433

VALUE
rb_f_exec(int argc, VALUE *argv)
{
    VALUE execarg_obj, fail_str;
    struct rb_execarg *eargp;
#define CHILD_ERRMSG_BUFLEN 80
    char errmsg[CHILD_ERRMSG_BUFLEN] = { '\0' };

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

#if defined(__APPLE__) || defined(__HAIKU__)
    rb_exec_without_timer_thread(eargp, errmsg, sizeof(errmsg));
#else
    rb_exec_async_signal_safe(eargp, errmsg, sizeof(errmsg));
#endif
    RB_GC_GUARD(execarg_obj);
    if (errmsg[0])
        rb_sys_fail(errmsg);
    rb_sys_fail_str(fail_str);
    return Qnil;		/* dummy */
}

- (Object) exit(status = true) - (Object) Kernel::exit(status = true) - (Object) 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 Kernel::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


3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
# File 'process.c', line 3644

VALUE
rb_f_exit(int argc, VALUE *argv)
{
    VALUE status;
    int istatus;

    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
	istatus = exit_status_code(status);
    }
    else {
	istatus = EXIT_SUCCESS;
    }
    rb_exit(istatus);

    UNREACHABLE;
}

- (Object) 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)


3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
# File 'process.c', line 3571

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

    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
	istatus = exit_status_code(status);
    }
    else {
	istatus = EXIT_FAILURE;
    }
    _exit(istatus);

    UNREACHABLE;
}

- (Object) raise - (Object) raise(string) - (Object) raise(exception[, string [, array]]) - (Object) fail - (Object) fail(string) - (Object) fail(exception[, string [, array]])

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 the name of an Exception class (or an object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the rescue clause of begin...end blocks.

raise "Failed to create socket"
raise ArgumentError, "No parameters", caller


581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
# File 'eval.c', line 581

static VALUE
rb_f_raise(int argc, VALUE *argv)
{
    VALUE err;
    if (argc == 0) {
	err = get_errinfo();
	if (!NIL_P(err)) {
	    argc = 1;
	    argv = &err;
	}
    }
    rb_raise_jump(rb_make_exception(argc, argv));

    UNREACHABLE;
}

- (Float) Float(arg)

Returns arg converted to a float. Numeric types are converted directly, the rest are converted using arg.to_f. As of Ruby 1.8, converting nil generates a TypeError.

Float(1)           #=> 1.0
Float("123.456")   #=> 123.456

Returns:



2763
2764
2765
2766
2767
# File 'object.c', line 2763

static VALUE
rb_f_float(VALUE obj, VALUE arg)
{
    return rb_Float(arg);
}

- (Fixnum?) fork { ... } - (Fixnum?) fork { ... }

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 Kernel.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 avaiable on some platforms like Windows and NetBSD 4. Therefore you should use spawn() instead of fork().

Overloads:



3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
# File 'process.c', line 3507

static VALUE
rb_f_fork(VALUE obj)
{
    rb_pid_t pid;

    rb_secure(2);

    switch (pid = rb_fork_ruby(NULL)) {
      case 0:
	rb_thread_atfork();
	if (rb_block_given_p()) {
	    int status;

	    rb_protect(rb_yield, Qundef, &status);
	    ruby_stop(status);
	}
	return Qnil;

      case -1:
	rb_sys_fail("fork(2)");
	return Qnil;

      default:
	return PIDT2NUM(pid);
    }
}

- (String) format(format_string[, arguments...]) - (String) sprintf(format_string[, arguments...])

Returns the string resulting from applying format_string to any additional arguments. Within the format string, any characters other than format sequences are copied to the result.

The syntax of a format sequence is follows.

%[flags][width][.precision]type

A format sequence consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character. The field type controls how the corresponding sprintf argument is to be interpreted, while the flags modify that interpretation.

The field type characters are:

Field |  Integer Format
------+--------------------------------------------------------------
  b   | Convert argument as a binary number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..1'.
  B   | Equivalent to `b', but uses an uppercase 0B for prefix
      | in the alternative format by #.
  d   | Convert argument as a decimal number.
  i   | Identical to `d'.
  o   | Convert argument as an octal number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..7'.
  u   | Identical to `d'.
  x   | Convert argument as a hexadecimal number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..f' (representing an infinite string of
      | leading 'ff's).
  X   | Equivalent to `x', but uses uppercase letters.

Field |  Float Format
------+--------------------------------------------------------------
  e   | Convert floating point argument into exponential notation
      | with one digit before the decimal point as [-]d.dddddde[+-]dd.
      | The precision specifies the number of digits after the decimal
      | point (defaulting to six).
  E   | Equivalent to `e', but uses an uppercase E to indicate
      | the exponent.
  f   | Convert floating point argument as [-]ddd.dddddd,
      | where the precision specifies the number of digits after
      | the decimal point.
  g   | Convert a floating point number using exponential form
      | if the exponent is less than -4 or greater than or
      | equal to the precision, or in dd.dddd form otherwise.
      | The precision specifies the number of significant digits.
  G   | Equivalent to `g', but use an uppercase `E' in exponent form.
  a   | Convert floating point argument as [-]0xh.hhhhp[+-]dd,
      | which is consisted from optional sign, "0x", fraction part
      | as hexadecimal, "p", and exponential part as decimal.
  A   | Equivalent to `a', but use uppercase `X' and `P'.

Field |  Other Format
------+--------------------------------------------------------------
  c   | Argument is the numeric code for a single character or
      | a single character string itself.
  p   | The valuing of argument.inspect.
  s   | Argument is a string to be substituted.  If the format
      | sequence contains a precision, at most that many characters
      | will be copied.
  %   | A percent sign itself will be displayed.  No argument taken.

The flags modifies the behavior of the formats. The flag characters are:

Flag     | Applies to    | Meaning
---------+---------------+-----------------------------------------
space    | bBdiouxX      | Leave a space at the start of
         | aAeEfgG       | non-negative numbers.
         | (numeric fmt) | For `o', `x', `X', `b' and `B', use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+-----------------------------------------
(digit)$ | all           | Specifies the absolute argument number
         |               | for this field.  Absolute and relative
         |               | argument numbers cannot be mixed in a
         |               | sprintf string.
---------+---------------+-----------------------------------------
 #       | bBoxX         | Use an alternative format.
         | aAeEfgG       | For the conversions `o', increase the precision
         |               | until the first digit will be `0' if
         |               | it is not formatted as complements.
         |               | For the conversions `x', `X', `b' and `B'
         |               | on non-zero, prefix the result with ``0x'',
         |               | ``0X'', ``0b'' and ``0B'', respectively.
         |               | For `a', `A', `e', `E', `f', `g', and 'G',
         |               | force a decimal point to be added,
         |               | even if no digits follow.
         |               | For `g' and 'G', do not remove trailing zeros.
---------+---------------+-----------------------------------------
+        | bBdiouxX      | Add a leading plus sign to non-negative
         | aAeEfgG       | numbers.
         | (numeric fmt) | For `o', `x', `X', `b' and `B', use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+-----------------------------------------
-        | all           | Left-justify the result of this conversion.
---------+---------------+-----------------------------------------
0 (zero) | bBdiouxX      | Pad with zeros, not spaces.
         | aAeEfgG       | For `o', `x', `X', `b' and `B', radix-1
         | (numeric fmt) | is used for negative numbers formatted as
         |               | complements.
---------+---------------+-----------------------------------------
*        | all           | Use the next argument as the field width.
         |               | If negative, left-justify the result. If the
         |               | asterisk is followed by a number and a dollar
         |               | sign, use the indicated argument as the width.

Examples of flags:

# `+' and space flag specifies the sign of non-negative numbers.
sprintf("%d", 123)  #=> "123"
sprintf("%+d", 123) #=> "+123"
sprintf("% d", 123) #=> " 123"

# `#' flag for `o' increases number of digits to show `0'.
# `+' and space flag changes format of negative numbers.
sprintf("%o", 123)   #=> "173"
sprintf("%#o", 123)  #=> "0173"
sprintf("%+o", -123) #=> "-173"
sprintf("%o", -123)  #=> "..7605"
sprintf("%#o", -123) #=> "..7605"

# `#' flag for `x' add a prefix `0x' for non-zero numbers.
# `+' and space flag disables complements for negative numbers.
sprintf("%x", 123)   #=> "7b"
sprintf("%#x", 123)  #=> "0x7b"
sprintf("%+x", -123) #=> "-7b"
sprintf("%x", -123)  #=> "..f85"
sprintf("%#x", -123) #=> "0x..f85"
sprintf("%#x", 0)    #=> "0"

# `#' for `X' uses the prefix `0X'.
sprintf("%X", 123)  #=> "7B"
sprintf("%#X", 123) #=> "0X7B"

# `#' flag for `b' add a prefix `0b' for non-zero numbers.
# `+' and space flag disables complements for negative numbers.
sprintf("%b", 123)   #=> "1111011"
sprintf("%#b", 123)  #=> "0b1111011"
sprintf("%+b", -123) #=> "-1111011"
sprintf("%b", -123)  #=> "..10000101"
sprintf("%#b", -123) #=> "0b..10000101"
sprintf("%#b", 0)    #=> "0"

# `#' for `B' uses the prefix `0B'.
sprintf("%B", 123)  #=> "1111011"
sprintf("%#B", 123) #=> "0B1111011"

# `#' for `e' forces to show the decimal point.
sprintf("%.0e", 1)  #=> "1e+00"
sprintf("%#.0e", 1) #=> "1.e+00"

# `#' for `f' forces to show the decimal point.
sprintf("%.0f", 1234)  #=> "1234"
sprintf("%#.0f", 1234) #=> "1234."

# `#' for `g' forces to show the decimal point.
# It also disables stripping lowest zeros.
sprintf("%g", 123.4)   #=> "123.4"
sprintf("%#g", 123.4)  #=> "123.400"
sprintf("%g", 123456)  #=> "123456"
sprintf("%#g", 123456) #=> "123456."

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

# padding is done by spaces,       width=20
# 0 or radix-1.             <------------------>
sprintf("%20d", 123)   #=> "                 123"
sprintf("%+20d", 123)  #=> "                +123"
sprintf("%020d", 123)  #=> "00000000000000000123"
sprintf("%+020d", 123) #=> "+0000000000000000123"
sprintf("% 020d", 123) #=> " 0000000000000000123"
sprintf("%-20d", 123)  #=> "123                 "
sprintf("%-+20d", 123) #=> "+123                "
sprintf("%- 20d", 123) #=> " 123                "
sprintf("%020x", -123) #=> "..ffffffffffffffff85"

For numeric fields, the precision controls the number of decimal places displayed. For string fields, the precision determines the maximum number of characters to be copied from the string. (Thus, the format sequence %10.10s will always contribute exactly ten characters to the result.)

Examples of precisions:

# precision for `d', 'o', 'x' and 'b' is
# minimum number of digits               <------>
sprintf("%20.8d", 123)  #=> "            00000123"
sprintf("%20.8o", 123)  #=> "            00000173"
sprintf("%20.8x", 123)  #=> "            0000007b"
sprintf("%20.8b", 123)  #=> "            01111011"
sprintf("%20.8d", -123) #=> "           -00000123"
sprintf("%20.8o", -123) #=> "            ..777605"
sprintf("%20.8x", -123) #=> "            ..ffff85"
sprintf("%20.8b", -11)  #=> "            ..110101"

# "0x" and "0b" for `#x' and `#b' is not counted for
# precision but "0" for `#o' is counted.  <------>
sprintf("%#20.8d", 123)  #=> "            00000123"
sprintf("%#20.8o", 123)  #=> "            00000173"
sprintf("%#20.8x", 123)  #=> "          0x0000007b"
sprintf("%#20.8b", 123)  #=> "          0b01111011"
sprintf("%#20.8d", -123) #=> "           -00000123"
sprintf("%#20.8o", -123) #=> "            ..777605"
sprintf("%#20.8x", -123) #=> "          0x..ffff85"
sprintf("%#20.8b", -11)  #=> "          0b..110101"

# precision for `e' is number of
# digits after the decimal point           <------>
sprintf("%20.8e", 1234.56789) #=> "      1.23456789e+03"

# precision for `f' is number of
# digits after the decimal point               <------>
sprintf("%20.8f", 1234.56789) #=> "       1234.56789000"

# precision for `g' is number of
# significant digits                          <------->
sprintf("%20.8g", 1234.56789) #=> "           1234.5679"

#                                         <------->
sprintf("%20.8g", 123456789)  #=> "       1.2345679e+08"

# precision for `s' is
# maximum number of characters                    <------>
sprintf("%20.8s", "string test") #=> "            string t"

Examples:

sprintf("%d %04x", 123, 123)               #=> "123 007b"
sprintf("%08b '%4s'", 123, 123)            #=> "01111011 ' 123'"
sprintf("%1$*2$s %2$d %1$s", "hello", 8)   #=> "   hello 8 hello"
sprintf("%1$*2$s %2$d", "hello", -8)       #=> "hello    -8"
sprintf("%+g:% g:%-g", 1.23, 1.23, 1.23)   #=> "+1.23: 1.23:1.23"
sprintf("%u", -123)                        #=> "-123"

For more complex formatting, Ruby supports a reference by name. %<name>s style uses format style, but %name style doesn't.

Examples:

sprintf("%<foo>d : %<bar>f", { :foo => 1, :bar => 2 })
  #=> 1 : 2.000000
sprintf("%{foo}f", { :foo => 1 })
  # => "1f"

Overloads:

  • - (String) format(format_string[, arguments...])

    Returns:

  • - (String) sprintf(format_string[, arguments...])

    Returns:



411
412
413
414
415
# File 'sprintf.c', line 411

VALUE
rb_f_sprintf(int argc, const VALUE *argv)
{
    return rb_str_format(argc - 1, argv + 1, GETNTHARG(0));
}

- (String?) gets(sep = $/) - (String?) gets(limit) - (String?) gets(sep, limit)

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.

Overloads:



7900
7901
7902
7903
7904
7905
7906
7907
# File 'io.c', line 7900

static VALUE
rb_f_gets(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_gets(argc, argv, argf);
    }
    return rb_funcall2(argf, idGets, argc, argv);
}

- (Array) global_variables

Returns an array of the names of global variables.

global_variables.grep /std/   #=> [:$stdin, :$stdout, :$stderr]

Returns:



839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
# File 'variable.c', line 839

VALUE
rb_f_global_variables(void)
{
    VALUE ary = rb_ary_new();
    char buf[2];
    int i;

    st_foreach_safe(rb_global_tbl, gvar_i, ary);
    buf[0] = '$';
    for (i = 1; i <= 9; ++i) {
	buf[1] = (char)(i + '0');
	rb_ary_push(ary, ID2SYM(rb_intern2(buf, 2)));
    }
    return ary;
}

- (Hash) Hash(arg)

Converts arg to a Hash by calling arg.to_hash. Returns an empty Hash when arg is nil or [].

Hash([])          #=> {}
Hash(nil)         #=> {}
Hash(key: :value) #=> {:key => :value}
Hash([1, 2, 3])   #=> TypeError

Returns:



2903
2904
2905
2906
2907
# File 'object.c', line 2903

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

- (Integer) Integer(arg, base = 0)

Converts arg to a Fixnum or Bignum. Numeric types are converted directly (with floating point numbers being truncated). base (0, or between 2 and 36) is a base for integer string representation. If arg is a String, when base is omitted or equals to zero, radix indicators (0, 0b, and 0x) are honored. In any case, strings should be strictly conformed to numeric representation. This behavior is different from that of String#to_i. Non string values will be converted using to_int, and to_i.

Integer(123.999)    #=> 123
Integer("0x1a")     #=> 26
Integer(Time.new)   #=> 1204973019
Integer("0930", 10) #=> 930
Integer("111", 2)   #=> 7

Returns:



2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
# File 'object.c', line 2593

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

    switch (argc) {
      case 2:
	base = NUM2INT(argv[1]);
      case 1:
	arg = argv[0];
	break;
      default:
	/* should cause ArgumentError */
	rb_scan_args(argc, argv, "11", NULL, NULL);
    }
    return rb_convert_to_integer(arg, base);
}

- (Boolean) block_given? - (Boolean) iterator?

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"

Overloads:

  • - (Boolean) block_given?

    Returns:

    • (Boolean)
  • - (Boolean) iterator?

    Returns:

    • (Boolean)

Returns:

  • (Boolean)


1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
# File 'vm_eval.c', line 1922

VALUE
rb_f_block_given_p(void)
{
    rb_thread_t *th = GET_THREAD();
    rb_control_frame_t *cfp = th->cfp;
    cfp = vm_get_ruby_level_caller_cfp(th, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));

    if (cfp != 0 && VM_CF_BLOCK_PTR(cfp)) {
	return Qtrue;
    }
    else {
	return Qfalse;
    }
}

- (Proc) lambda {|...| ... }

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

Yields:

  • (...)

Returns:



650
651
652
653
654
# File 'proc.c', line 650

VALUE
rb_block_lambda(void)
{
    return proc_new(rb_cProc, TRUE);
}

- (true) load(filename, wrap = false)

Loads and executes the Ruby program in the file filename. If the filename does not resolve to an absolute path, the file is searched for in the library directories listed in $:. If the optional wrap parameter is true, the loaded script will be executed under an anonymous module, protecting the calling program's global namespace. In no circumstance will any local variables in the loaded file be propagated to the loading environment.

Returns:

  • (true)


660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
# File 'load.c', line 660

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

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

    if (RUBY_DTRACE_LOAD_ENTRY_ENABLED()) {
	RUBY_DTRACE_LOAD_ENTRY(StringValuePtr(fname),
			       rb_sourcefile(),
			       rb_sourceline());
    }

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

    if (RUBY_DTRACE_LOAD_RETURN_ENABLED()) {
	RUBY_DTRACE_LOAD_RETURN(StringValuePtr(fname),
			       rb_sourcefile(),
			       rb_sourceline());
    }

    return Qtrue;
}

- (Array) local_variables

Returns the names of the current local variables.

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

Returns:



1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
# File 'vm_eval.c', line 1858

static VALUE
rb_f_local_variables(void)
{
    VALUE ary = rb_ary_new();
    rb_thread_t *th = GET_THREAD();
    rb_control_frame_t *cfp =
	vm_get_ruby_level_caller_cfp(th, RUBY_VM_PREVIOUS_CONTROL_FRAME(th->cfp));
    int i;

    while (cfp) {
	if (cfp->iseq) {
	    for (i = 0; i < cfp->iseq->local_table_size; i++) {
		ID lid = cfp->iseq->local_table[i];
		if (lid) {
		    const char *vname = rb_id2name(lid);
		    /* should skip temporary variable */
		    if (vname) {
			rb_ary_push(ary, ID2SYM(lid));
		    }
		}
	    }
	}
	if (!VM_EP_LEP_P(cfp->ep)) {
	    /* block */
	    VALUE *ep = VM_CF_PREV_EP(cfp);

	    if (vm_collect_local_variables_in_heap(th, ep, ary)) {
		break;
	    }
	    else {
		while (cfp->ep != ep) {
		    cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
		}
	    }
	}
	else {
	    break;
	}
    }
    return ary;
}

- (Object) loop { ... } - (Object) loop

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.

Overloads:

  • - (Object) loop { ... }

    Yields:



1025
1026
1027
1028
1029
1030
1031
# File 'vm_eval.c', line 1025

static VALUE
rb_f_loop(VALUE self)
{
    RETURN_SIZED_ENUMERATOR(self, 0, 0, rb_f_loop_size);
    rb_rescue2(loop_i, (VALUE)0, 0, 0, rb_eStopIteration, (VALUE)0);
    return Qnil;		/* dummy */
}

- (IO?) open(path[, mode [, perm]][, opt]) - (Object) open(path[, mode [, perm]][, opt]) {|io| ... }

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

If path does not start with a pipe character (|), treat it as the name of a file to open using the specified mode (defaulting to "r").

The mode is either a string or an integer. If it is an integer, it must be bitwise-or of open(2) flags, such as File::RDWR or File::EXCL. If it is a string, it is either "fmode", "fmode:ext_enc", or "fmode:ext_enc:int_enc".

See the documentation of IO.new for full documentation of the mode string directives.

If a file is being created, its initial permissions may be set using the perm parameter. See File.new and the open(2) and chmod(2) man pages for a description of permissions.

If a block is specified, it will be invoked with the IO object as a parameter, and the IO will be automatically closed when the block terminates. The call returns the value of the block.

If path starts with a pipe character ("|"), a subprocess is created, connected to the caller by a pair of pipes. The returned IO object may be used to write to the standard input and read from the standard output of this subprocess.

If the command following the pipe is a single minus sign ("|-"), Ruby forks, and this subprocess is connected to the parent. If the command is not "-", the subprocess runs the command.

When the subprocess is ruby (opened via "|-"), the open call returns nil. If a block is associated with the open call, that block will run twice --- once in the parent and once in the child.

The block parameter will be an IO object in the parent and nil in the child. The parent's IO object will be connected to the child's $stdin and $stdout. The subprocess will be terminated at the end of the block.

Examples

Reading from "testfile":

open("testfile") do |f|
  print f.gets
end

Produces:

This is line one

Open a subprocess and read its output:

cmd = open("|date")
print cmd.gets
cmd.close

Produces:

Wed Apr  9 08:56:31 CDT 2003

Open a subprocess running the same Ruby program:

f = open("|-", "w+")
if f == nil
  puts "in Child"
  exit
else
  puts "Got: #{f.gets}"
end

Produces:

Got: in Child

Open a subprocess using a block to receive the IO object:

open "|-" do |f|
  if f then
    # parent process
    puts "Got: #{f.gets}"
  else
    # child process
    puts "in Child"
  end
end

Produces:

Got: in Child

Overloads:

  • - (IO?) open(path[, mode [, perm]][, opt])

    Returns:

    • (IO, nil)
  • - (Object) open(path[, mode [, perm]][, opt]) {|io| ... }

    Yields:

    • (io)

    Returns:



6372
6373
6374
6375
6376
6377
6378
6379
6380
6381
6382
6383
6384
6385
6386
6387
6388
6389
6390
6391
6392
6393
6394
6395
6396
6397
6398
6399
6400
6401
6402
6403
6404
6405
6406
6407
# File 'io.c', line 6372

static VALUE
rb_f_open(int argc, VALUE *argv)
{
    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_funcall2(argv[0], to_open, argc-1, argv+1);

	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);
}

- (Object) p(obj) - (Array) p(obj1, obj2, ...) - (nil) p

For each object, directly writes obj.inspect followed by a newline to the program's standard output.

S = Struct.new(:name, :state)
s = S['dave', 'TX']
p s

produces:

#<S name="dave", state="TX">

Overloads:



7016
7017
7018
7019
7020
7021
7022
7023
7024
# File 'io.c', line 7016

static VALUE
rb_f_p(int argc, VALUE *argv, VALUE self)
{
    struct rb_f_p_arg arg;
    arg.argc = argc;
    arg.argv = argv;

    return rb_uninterruptible(rb_f_p_internal, (VALUE)&arg);
}

Prints each object in turn to $stdout. If the output field separator ($,) is not nil, its contents will appear between each field. If the output record separator ($\</code>) is not nil, it will be appended to the output. If no arguments are given, prints <code>$_. Objects that aren't strings will be converted by calling their to_s method.

print "cat", [1,2,3], 99, "\n"
$, = ", "
$\ = "\n"
print "cat", [1,2,3], 99

produces:

cat12399
cat, 1, 2, 3, 99

Returns:

  • (nil)


6788
6789
6790
6791
6792
6793
# File 'io.c', line 6788

static VALUE
rb_f_print(int argc, VALUE *argv)
{
    rb_io_print(argc, argv, rb_stdout);
    return Qnil;
}

- (nil) printf(io, string[, obj ... ]) - (nil) printf(string[, obj ... ])

Equivalent to:

io.write(sprintf(string, obj, ...)

or

$stdout.write(sprintf(string, obj, ...)

Overloads:

  • - (nil) printf(io, string[, obj ... ])

    Returns:

    • (nil)
  • - (nil) printf(string[, obj ... ])

    Returns:

    • (nil)


6699
6700
6701
6702
6703
6704
6705
6706
6707
6708
6709
6710
6711
6712
6713
6714
6715
6716
# File 'io.c', line 6699

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

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

    return Qnil;
}

- (Proc) proc {|...| ... }

Equivalent to Proc.new.

Yields:

  • (...)

Returns:



636
637
638
639
640
# File 'proc.c', line 636

VALUE
rb_block_proc(void)
{
    return proc_new(rb_cProc, FALSE);
}

- (Integer) putc(int)

Equivalent to:

$stdout.putc(int)

Refer to the documentation for IO#putc for important information regarding multi-byte characters.

Returns:



6840
6841
6842
6843
6844
6845
6846
6847
# File 'io.c', line 6840

static VALUE
rb_f_putc(VALUE recv, VALUE ch)
{
    if (recv == rb_stdout) {
	return rb_io_putc(recv, ch);
    }
    return rb_funcall2(rb_stdout, rb_intern("putc"), 1, &ch);
}

- (nil) puts(obj, ...)

Equivalent to

$stdout.puts(obj, ...)

Returns:

  • (nil)


6945
6946
6947
6948
6949
6950
6951
6952
# File 'io.c', line 6945

static VALUE
rb_f_puts(int argc, VALUE *argv, VALUE recv)
{
    if (recv == rb_stdout) {
	return rb_io_puts(argc, argv, recv);
    }
    return rb_funcall2(rb_stdout, rb_intern("puts"), argc, argv);
}

- (Object) raise - (Object) raise(string) - (Object) raise(exception[, string [, array]]) - (Object) fail - (Object) fail(string) - (Object) fail(exception[, string [, array]])

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 the name of an Exception class (or an object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the rescue clause of begin...end blocks.

raise "Failed to create socket"
raise ArgumentError, "No parameters", caller


581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
# File 'eval.c', line 581

static VALUE
rb_f_raise(int argc, VALUE *argv)
{
    VALUE err;
    if (argc == 0) {
	err = get_errinfo();
	if (!NIL_P(err)) {
	    argc = 1;
	    argv = &err;
	}
    }
    rb_raise_jump(rb_make_exception(argc, argv));

    UNREACHABLE;
}

- (Numeric) rand(max = 0)

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

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

See also Random.rand.

Returns:



1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
# File 'random.c', line 1202

static VALUE
rb_f_rand(int argc, VALUE *argv, VALUE obj)
{
    VALUE v, vmax, r;
    struct MT *mt = default_mt();

    if (argc == 0) goto zero_arg;
    rb_scan_args(argc, argv, "01", &vmax);
    if (NIL_P(vmax)) goto zero_arg;
    if ((v = rand_range(mt, vmax)) != Qfalse) {
	return v;
    }
    vmax = rb_to_int(vmax);
    if (vmax == INT2FIX(0) || NIL_P(r = rand_int(mt, vmax, 0))) {
      zero_arg:
	return DBL2NUM(genrand_real(mt));
    }
    return r;
}

- (Numeric) Rational(x[, y])

Returns x/y;

Rational(1, 2)   #=> (1/2)
Rational('1/2')  #=> (1/2)

Syntax of 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 String#to_r.

Returns:



591
592
593
594
595
# File 'rational.c', line 591

static VALUE
nurat_f_rational(int argc, VALUE *argv, VALUE klass)
{
    return rb_funcall2(rb_cRational, id_convert, argc, argv);
}

- (String) readline(sep = $/) - (String) readline(limit) - (String) readline(sep, limit)

Equivalent to Kernel::gets, except readline raises EOFError at end of file.

Overloads:



7973
7974
7975
7976
7977
7978
7979
7980
# File 'io.c', line 7973

static VALUE
rb_f_readline(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_readline(argc, argv, argf);
    }
    return rb_funcall2(argf, rb_intern("readline"), argc, argv);
}

- (Array) readlines(sep = $/) - (Array) readlines(limit) - (Array) readlines(sep, limit)

Returns an array containing the lines returned by calling Kernel.gets(sep) until the end of file.

Overloads:



8026
8027
8028
8029
8030
8031
8032
8033
# File 'io.c', line 8026

static VALUE
rb_f_readlines(int argc, VALUE *argv, VALUE recv)
{
    if (recv == argf) {
	return argf_readlines(argc, argv, argf);
    }
    return rb_funcall2(argf, rb_intern("readlines"), argc, argv);
}

- (Boolean) require(name)

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

If the filename does not resolve to an absolute path, it will be searched for in the directories listed in $LOAD_PATH ($:).

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.

Returns:

  • (Boolean)


784
785
786
787
788
# File 'load.c', line 784

VALUE
rb_f_require(VALUE obj, VALUE fname)
{
    return rb_require_safe(fname, rb_safe_level());
}

- (Boolean) require_relative(string)

Ruby tries to load the library named string relative to the requiring file's path. If the file's path cannot be determined a LoadError is raised. If a file is loaded true is returned and false otherwise.

Returns:

  • (Boolean)


798
799
800
801
802
803
804
805
806
807
# File 'load.c', line 798

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_safe(rb_file_absolute_path(fname, base), rb_safe_level());
}

- (Object) select(read_array)

[, error_array

[, timeout]]]) -> array  or  nil

Calls select(2) system call. It monitors given arrays of IO objects, waits one or more of IO objects ready for reading, are ready for writing, and have pending exceptions respectively, and returns an array that contains arrays of those IO objects. It will return nil if optional timeout value is given and no IO object is ready in timeout seconds.

Parameters

read_array

an array of IO objects that wait until ready for read

write_array

an array of IO objects that wait until ready for write

error_array

an array of IO objects that wait for exceptions

timeout

a numeric value in second

Example

rp, wp = IO.pipe
mesg = "ping "
100.times {
  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
}

produces:

ping pong
ping pong
ping pong
(snipped)
ping


8483
8484
8485
8486
8487
8488
8489
8490
8491
8492
8493
8494
8495
8496
8497
8498
8499
8500
8501
8502
8503
8504
# File 'io.c', line 8483

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);
}

- (Fixnum) sleep([duration])

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

Returns:



4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
# File 'process.c', line 4161

static VALUE
rb_f_sleep(int argc, VALUE *argv)
{
    time_t beg, end;

    beg = time(0);
    if (argc == 0) {
	rb_thread_sleep_forever();
    }
    else {
	rb_check_arity(argc, 0, 1);
	rb_thread_wait_for(rb_time_interval(argv[0]));
    }

    end = time(0) - beg;

    return INT2FIX(end);
}

- (Object) spawn([env,][,options]) - (Object) spawn([env,][,options])

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 Kernel#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
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 to 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 => true  : don't 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 or positive integer. true and zero means the process should be a process leader of a new process group. Other values specifies a process group to be belongs.

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, a fixnum, 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, 3=>"/dev/null") # read mode

For stdout and stderr, 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 true 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 Kernel.exec for the standard shell.



4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
# File 'process.c', line 4114

static VALUE
rb_f_spawn(int argc, VALUE *argv)
{
    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);
    eargp = rb_execarg_get(execarg_obj);
    rb_execarg_fixup(execarg_obj);
    fail_str = eargp->use_shell ? eargp->invoke.sh.shell_script : eargp->invoke.cmd.command_name;

    pid = rb_spawn_process(eargp, errmsg, sizeof(errmsg));
    RB_GC_GUARD(execarg_obj);

    if (pid == -1) {
	const char *prog = errmsg;
	if (!prog[0]) {
	    rb_sys_fail_str(fail_str);
	}
	rb_sys_fail(prog);
    }
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    return PIDT2NUM(pid);
#else
    return Qnil;
#endif
}

- (String) format(format_string[, arguments...]) - (String) sprintf(format_string[, arguments...])

Returns the string resulting from applying format_string to any additional arguments. Within the format string, any characters other than format sequences are copied to the result.

The syntax of a format sequence is follows.

%[flags][width][.precision]type

A format sequence consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character. The field type controls how the corresponding sprintf argument is to be interpreted, while the flags modify that interpretation.

The field type characters are:

Field |  Integer Format
------+--------------------------------------------------------------
  b   | Convert argument as a binary number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..1'.
  B   | Equivalent to `b', but uses an uppercase 0B for prefix
      | in the alternative format by #.
  d   | Convert argument as a decimal number.
  i   | Identical to `d'.
  o   | Convert argument as an octal number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..7'.
  u   | Identical to `d'.
  x   | Convert argument as a hexadecimal number.
      | Negative numbers will be displayed as a two's complement
      | prefixed with `..f' (representing an infinite string of
      | leading 'ff's).
  X   | Equivalent to `x', but uses uppercase letters.

Field |  Float Format
------+--------------------------------------------------------------
  e   | Convert floating point argument into exponential notation
      | with one digit before the decimal point as [-]d.dddddde[+-]dd.
      | The precision specifies the number of digits after the decimal
      | point (defaulting to six).
  E   | Equivalent to `e', but uses an uppercase E to indicate
      | the exponent.
  f   | Convert floating point argument as [-]ddd.dddddd,
      | where the precision specifies the number of digits after
      | the decimal point.
  g   | Convert a floating point number using exponential form
      | if the exponent is less than -4 or greater than or
      | equal to the precision, or in dd.dddd form otherwise.
      | The precision specifies the number of significant digits.
  G   | Equivalent to `g', but use an uppercase `E' in exponent form.
  a   | Convert floating point argument as [-]0xh.hhhhp[+-]dd,
      | which is consisted from optional sign, "0x", fraction part
      | as hexadecimal, "p", and exponential part as decimal.
  A   | Equivalent to `a', but use uppercase `X' and `P'.

Field |  Other Format
------+--------------------------------------------------------------
  c   | Argument is the numeric code for a single character or
      | a single character string itself.
  p   | The valuing of argument.inspect.
  s   | Argument is a string to be substituted.  If the format
      | sequence contains a precision, at most that many characters
      | will be copied.
  %   | A percent sign itself will be displayed.  No argument taken.

The flags modifies the behavior of the formats. The flag characters are:

Flag     | Applies to    | Meaning
---------+---------------+-----------------------------------------
space    | bBdiouxX      | Leave a space at the start of
         | aAeEfgG       | non-negative numbers.
         | (numeric fmt) | For `o', `x', `X', `b' and `B', use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+-----------------------------------------
(digit)$ | all           | Specifies the absolute argument number
         |               | for this field.  Absolute and relative
         |               | argument numbers cannot be mixed in a
         |               | sprintf string.
---------+---------------+-----------------------------------------
 #       | bBoxX         | Use an alternative format.
         | aAeEfgG       | For the conversions `o', increase the precision
         |               | until the first digit will be `0' if
         |               | it is not formatted as complements.
         |               | For the conversions `x', `X', `b' and `B'
         |               | on non-zero, prefix the result with ``0x'',
         |               | ``0X'', ``0b'' and ``0B'', respectively.
         |               | For `a', `A', `e', `E', `f', `g', and 'G',
         |               | force a decimal point to be added,
         |               | even if no digits follow.
         |               | For `g' and 'G', do not remove trailing zeros.
---------+---------------+-----------------------------------------
+        | bBdiouxX      | Add a leading plus sign to non-negative
         | aAeEfgG       | numbers.
         | (numeric fmt) | For `o', `x', `X', `b' and `B', use
         |               | a minus sign with absolute value for
         |               | negative values.
---------+---------------+-----------------------------------------
-        | all           | Left-justify the result of this conversion.
---------+---------------+-----------------------------------------
0 (zero) | bBdiouxX      | Pad with zeros, not spaces.
         | aAeEfgG       | For `o', `x', `X', `b' and `B', radix-1
         | (numeric fmt) | is used for negative numbers formatted as
         |               | complements.
---------+---------------+-----------------------------------------
*        | all           | Use the next argument as the field width.
         |               | If negative, left-justify the result. If the
         |               | asterisk is followed by a number and a dollar
         |               | sign, use the indicated argument as the width.

Examples of flags:

# `+' and space flag specifies the sign of non-negative numbers.
sprintf("%d", 123)  #=> "123"
sprintf("%+d", 123) #=> "+123"
sprintf("% d", 123) #=> " 123"

# `#' flag for `o' increases number of digits to show `0'.
# `+' and space flag changes format of negative numbers.
sprintf("%o", 123)   #=> "173"
sprintf("%#o", 123)  #=> "0173"
sprintf("%+o", -123) #=> "-173"
sprintf("%o", -123)  #=> "..7605"
sprintf("%#o", -123) #=> "..7605"

# `#' flag for `x' add a prefix `0x' for non-zero numbers.
# `+' and space flag disables complements for negative numbers.
sprintf("%x", 123)   #=> "7b"
sprintf("%#x", 123)  #=> "0x7b"
sprintf("%+x", -123) #=> "-7b"
sprintf("%x", -123)  #=> "..f85"
sprintf("%#x", -123) #=> "0x..f85"
sprintf("%#x", 0)    #=> "0"

# `#' for `X' uses the prefix `0X'.
sprintf("%X", 123)  #=> "7B"
sprintf("%#X", 123) #=> "0X7B"

# `#' flag for `b' add a prefix `0b' for non-zero numbers.
# `+' and space flag disables complements for negative numbers.
sprintf("%b", 123)   #=> "1111011"
sprintf("%#b", 123)  #=> "0b1111011"
sprintf("%+b", -123) #=> "-1111011"
sprintf("%b", -123)  #=> "..10000101"
sprintf("%#b", -123) #=> "0b..10000101"
sprintf("%#b", 0)    #=> "0"

# `#' for `B' uses the prefix `0B'.
sprintf("%B", 123)  #=> "1111011"
sprintf("%#B", 123) #=> "0B1111011"

# `#' for `e' forces to show the decimal point.
sprintf("%.0e", 1)  #=> "1e+00"
sprintf("%#.0e", 1) #=> "1.e+00"

# `#' for `f' forces to show the decimal point.
sprintf("%.0f", 1234)  #=> "1234"
sprintf("%#.0f", 1234) #=> "1234."

# `#' for `g' forces to show the decimal point.
# It also disables stripping lowest zeros.
sprintf("%g", 123.4)   #=> "123.4"
sprintf("%#g", 123.4)  #=> "123.400"
sprintf("%g", 123456)  #=> "123456"
sprintf("%#g", 123456) #=> "123456."

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

# padding is done by spaces,       width=20
# 0 or radix-1.             <------------------>
sprintf("%20d", 123)   #=> "                 123"
sprintf("%+20d", 123)  #=> "                +123"
sprintf("%020d", 123)  #=> "00000000000000000123"
sprintf("%+020d", 123) #=> "+0000000000000000123"
sprintf("% 020d", 123) #=> " 0000000000000000123"
sprintf("%-20d", 123)  #=> "123                 "
sprintf("%-+20d", 123) #=> "+123                "
sprintf("%- 20d", 123) #=> " 123                "
sprintf("%020x", -123) #=> "..ffffffffffffffff85"

For numeric fields, the precision controls the number of decimal places displayed. For string fields, the precision determines the maximum number of characters to be copied from the string. (Thus, the format sequence %10.10s will always contribute exactly ten characters to the result.)

Examples of precisions:

# precision for `d', 'o', 'x' and 'b' is
# minimum number of digits               <------>
sprintf("%20.8d", 123)  #=> "            00000123"
sprintf("%20.8o", 123)  #=> "            00000173"
sprintf("%20.8x", 123)  #=> "            0000007b"
sprintf("%20.8b", 123)  #=> "            01111011"
sprintf("%20.8d", -123) #=> "           -00000123"
sprintf("%20.8o", -123) #=> "            ..777605"
sprintf("%20.8x", -123) #=> "            ..ffff85"
sprintf("%20.8b", -11)  #=> "            ..110101"

# "0x" and "0b" for `#x' and `#b' is not counted for
# precision but "0" for `#o' is counted.  <------>
sprintf("%#20.8d", 123)  #=> "            00000123"
sprintf("%#20.8o", 123)  #=> "            00000173"
sprintf("%#20.8x", 123)  #=> "          0x0000007b"
sprintf("%#20.8b", 123)  #=> "          0b01111011"
sprintf("%#20.8d", -123) #=> "           -00000123"
sprintf("%#20.8o", -123) #=> "            ..777605"
sprintf("%#20.8x", -123) #=> "          0x..ffff85"
sprintf("%#20.8b", -11)  #=> "          0b..110101"

# precision for `e' is number of
# digits after the decimal point           <------>
sprintf("%20.8e", 1234.56789) #=> "      1.23456789e+03"

# precision for `f' is number of
# digits after the decimal point               <------>
sprintf("%20.8f", 1234.56789) #=> "       1234.56789000"

# precision for `g' is number of
# significant digits                          <------->
sprintf("%20.8g", 1234.56789) #=> "           1234.5679"

#                                         <------->
sprintf("%20.8g", 123456789)  #=> "       1.2345679e+08"

# precision for `s' is
# maximum number of characters                    <------>
sprintf("%20.8s", "string test") #=> "            string t"

Examples:

sprintf("%d %04x", 123, 123)               #=> "123 007b"
sprintf("%08b '%4s'", 123, 123)            #=> "01111011 ' 123'"
sprintf("%1$*2$s %2$d %1$s", "hello", 8)   #=> "   hello 8 hello"
sprintf("%1$*2$s %2$d", "hello", -8)       #=> "hello    -8"
sprintf("%+g:% g:%-g", 1.23, 1.23, 1.23)   #=> "+1.23: 1.23:1.23"
sprintf("%u", -123)                        #=> "-123"

For more complex formatting, Ruby supports a reference by name. %<name>s style uses format style, but %name style doesn't.

Examples:

sprintf("%<foo>d : %<bar>f", { :foo => 1, :bar => 2 })
  #=> 1 : 2.000000
sprintf("%{foo}f", { :foo => 1 })
  # => "1f"

Overloads:

  • - (String) format(format_string[, arguments...])

    Returns:

  • - (String) sprintf(format_string[, arguments...])

    Returns:



411
412
413
414
415
# File 'sprintf.c', line 411

VALUE
rb_f_sprintf(int argc, const VALUE *argv)
{
    return rb_str_format(argc - 1, argv + 1, GETNTHARG(0));
}

- (Object) srand(number = Random.new_seed)

Seeds the system pseudo-random number generator, Random::DEFAULT, 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]


684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
# File 'random.c', line 684

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

    if (argc == 0) {
	seed = random_seed();
    }
    else {
	rb_scan_args(argc, argv, "01", &seed);
    }
    old = r->seed;
    r->seed = rand_init(&r->mt, seed);

    return old;
}

- (String) String(arg)

Converts arg to a String by calling its to_s method.

String(self)        #=> "main"
String(self.class)  #=> "Object"
String(123456)      #=> "123456"

Returns:



2837
2838
2839
2840
2841
# File 'object.c', line 2837

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

- (Integer) syscall(num[, args...])

Calls the operating system function identified by num and returns the result of the function or raises SystemCallError if it failed.

Arguments for the function can follow num. They must be either String objects or Integer objects. A String object is passed as a pointer to the byte sequence. An Integer object is passed as an integer whose bit size is same as a pointer. Up to nine parameters may be passed (14 on the Atari-ST).

The function identified by num is system dependent. On some Unix systems, the numbers may be obtained from a header file called syscall.h.

syscall 4, 1, "hello\n", 6   # '4' is write(2) on our box

produces:

hello

Calling syscall on a platform which does not have any way to an arbitrary system function just fails with NotImplementedError.

Note

syscall is essentially unsafe and unportable. Feel free to shoot your foot. DL (Fiddle) library is preferred for safer and a bit more portable programming.

Returns:



8942
8943
8944
8945
8946
8947
8948
8949
8950
8951
8952
8953
8954
8955
8956
8957
8958
8959
8960
8961
8962
8963
8964
8965
8966
8967
8968
8969
8970
8971
8972
8973
8974
8975
8976
8977
8978
8979
8980
8981
8982
8983
8984
8985
8986
8987
8988
8989
8990
8991
8992
8993
8994
8995
8996
8997
8998
8999
9000
9001
9002
9003
9004
9005
9006
9007
9008
9009
9010
9011
9012
9013
9014
9015
9016
9017
9018
9019
9020
9021
9022
9023
9024
9025
9026
9027
9028
9029
9030
9031
9032
9033
9034
9035
9036
9037
9038
9039
9040
9041
9042
9043
9044
9045
9046
9047
9048
9049
9050
9051
9052
9053
9054
9055
9056
9057
9058
9059
9060
9061
9062
9063
# File 'io.c', line 8942

static VALUE
rb_f_syscall(int argc, VALUE *argv)
{
#ifdef atarist
    VALUE arg[13]; /* yes, we really need that many ! */
#else
    VALUE arg[8];
#endif
#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_warning("We plan to remove a syscall function at future release. DL(Fiddle) provides safer alternative.");
    }

    rb_secure(2);
    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;
#ifdef atarist
      case 9:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7]);
	break;
      case 10:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8]);
	break;
      case 11:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9]);
	break;
      case 12:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10]);
	break;
      case 13:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10], arg[11]);
	break;
      case 14:
	retval = SYSCALL(num, arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
	  arg[7], arg[8], arg[9], arg[10], arg[11], arg[12]);
        break;
#endif
    }

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

- (true, ...) system([env,][,options])

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

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

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

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

produces:

config.h main.rb
*

See Kernel.exec for the standard shell.

Returns:

  • (true, false, nil)


3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
# File 'process.c', line 3813

static VALUE
rb_f_system(int argc, VALUE *argv)
{
    rb_pid_t pid;
    int status;

#if defined(SIGCLD) && !defined(SIGCHLD)
# define SIGCHLD SIGCLD
#endif

#ifdef SIGCHLD
    RETSIGTYPE (*chfunc)(int);

    rb_last_status_clear();
    chfunc = signal(SIGCHLD, SIG_DFL);
#endif
    pid = rb_spawn_internal(argc, argv, NULL, 0);
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    if (pid > 0) {
        int ret, status;
        ret = rb_waitpid(pid, &status, 0);
        if (ret == (rb_pid_t)-1)
            rb_sys_fail("Another thread waited the process started by system().");
    }
#endif
#ifdef SIGCHLD
    signal(SIGCHLD, chfunc);
#endif
    if (pid < 0) {
	return Qnil;
    }
    status = PST2INT(rb_last_status_get());
    if (status == EXIT_SUCCESS) return Qtrue;
    return Qfalse;
}

- (Object) test(cmd, file1[, file2])

Uses the integer 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

Returns:



4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
# File 'file.c', line 4460

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

    if (argc == 0) rb_check_arity(argc, 2, 3);
    cmd = NUM2CHR(argv[0]);
    if (cmd == 0) {
      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);
	}
    }
    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 'a':
	  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) {
	    FilePathValue(fname);
	    rb_sys_fail_path(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;

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

	switch (cmd) {
	  case '=':
	    if (st1.st_mtime == st2.st_mtime) return Qtrue;
	    return Qfalse;

	  case '>':
	    if (st1.st_mtime > st2.st_mtime) return Qtrue;
	    return Qfalse;

	  case '<':
	    if (st1.st_mtime < st2.st_mtime) return Qtrue;
	    return Qfalse;
	}
    }
    goto unknown;
}

- (Object) throw(tag[, obj])

Transfers control to the end of the active catch block waiting for tag. Raises ArgumentError 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 Kernel::catch.



1713
1714
1715
1716
1717
1718
1719
1720
1721
# File 'vm_eval.c', line 1713

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

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

- (Object) trace_var

- (Object) trap(signal, command) - (Object) trap(signal) {|| ... }

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

Overloads:



1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
# File 'signal.c', line 1010

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

    rb_secure(2);
    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 (OBJ_TAINTED(cmd)) {
	rb_raise(rb_eSecurityError, "Insecure: tainted signal trap");
    }

    return trap(sig, func, cmd);
}

- (Object) untrace_var

- (nil) warn(msg, ...)

Displays each of the given messages followed by a record separator on STDERR unless warnings have been disabled (for example with the -W0 flag).

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

<em>produces:</em>

  warning 1
  warning 2

Returns:

  • (nil)


258
259
260
261
262
263
264
265
# File 'error.c', line 258

static VALUE
rb_warn_m(int argc, VALUE *argv, VALUE exc)
{
    if (!NIL_P(ruby_verbose) && argc > 0) {
	rb_io_puts(argc, argv, rb_stderr);
    }
    return Qnil;
}

Commenting is here to help enhance the documentation. For example, sample code, or clarification of the documentation.

If you have questions about Ruby or the documentation, please post to one of the Ruby mailing lists. You will get better, faster, help that way.

If you wish to post a correction of the docs, please do so, but also file bug report so that it can be corrected for the next release. Thank you.

blog comments powered by Disqus