Kernel

Inheritance

Object is the parent class of all classes in Ruby. Its methods are therefore available to all objects unless explicitly overridden.

Object mixes in the Kernel module, making the built-in kernel functions globally accessible. Although the instance methods of Object are defined by the Kernel module, we have chosen to document them here for clarity.

In the descriptions of Object‘s methods, the parameter symbol refers to a symbol, which is either a quoted string or a Symbol (such as :name).

Methods

Instance

Visibility	Signature
public	Array (p1)
public	Float (p1)
public	Integer (p1)
public	String (p1)
public	URI (uri_str)
public	__method__ ()
public	` (p1)
public	abort (...)
public	at_exit ()
public	autoload (p1, p2)
public	autoload? (p1)
public	binding ()
public	block_given? ()
public	callcc ()
public	caller (...)
public	catch (p1)
public	chomp (...)
public	chomp! (...)
public	chop ()
public	chop! ()
public	eval (...)
public	exec (...)
public	exit (...)
public	exit! (...)
public	fail (...)
public	fork ()
public	format (...)
public	getc ()
public	gets (...)
public	global_variables ()
public	gsub (...)
public	gsub! (...)
public	iterator? ()
public	lambda ()
public	load (...)
public	local_variables ()
public	loop ()
public	method_missing (...)
public	open (...)
public	p (...)
public	pretty_inspect ()
public	print (...)
public	printf (...)
public	proc ()
public	putc (p1)
public	puts (...)
public	raise (...)
public	rand (...)
public	readline (...)
public	readlines (...)
public	require (p1)
public	scan (p1)
public	select (...)
public	set_trace_func (p1)
public	sleep (...)
public	split (...)
public	sprintf (...)
public	srand (...)
public	sub (...)
public	sub! (...)
public	syscall (...)
public	system (...)
public	test (...)
public	throw (...)
public	trace_var (...)
public	trap (...)
public	untrace_var (...)
public	warn (msg)
public	warn (p1)

Instance Method Detail

Array(arg) => array

Returns arg as an Array. First tries to call arg.to_ary, then arg.to_a. If both fail, creates a single element array containing arg (unless arg is nil).

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

Float(arg) => float

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

Integer(arg) => integer

Converts arg to a Fixnum or Bignum. Numeric types are converted directly (with floating point numbers being truncated). If arg is a String, leading radix indicators (0, 0b, and 0x) are honored. Others are converted using to_int and to_i. This behavior is different from that of String#to_i.

   Integer(123.999)    #=> 123
   Integer("0x1a")     #=> 26
   Integer(Time.new)   #=> 1049896590

String(arg) => string

Converts arg to a String by calling its to_s method.

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

URI(uri_str)

alias for URI.parse.

This method is introduced at 1.8.2.

method => symbol

Returns the name of the current method as a Symbol. If called from inside of an aliased method it will return the original nonaliased name. If called outside of a method, it returns nil.

  def foo
    __method__
  end
  alias bar foo

  foo                # => :foo
  bar                # => :foo

`cmd` => 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

abort
Kernel::abort
Process::abort

Terminate execution immediately, effectively by calling Kernel.exit(1). If msg is given, it is written to STDERR prior to terminating.

at_exit { block } → proc

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

autoload(module, filename) => nil

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")

autoload(module, filename) => nil

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")

binding → a_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. Also see the description of class Binding.

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

block_given? => true or false
iterator? => true or false

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"

callcc {|cont| block } => obj

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

caller(start=1) => array

Returns the current execution stack—an array containing strings in the form ``file:line’’ or ``file:line: in `method‘’’. The optional start parameter determines the number of initial stack entries to omit from the result.

   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"]
   c(1)   #=> ["prog:5:in `b'", "prog:8:in `c'", "prog:11"]
   c(2)   #=> ["prog:8:in `c'", "prog:12"]
   c(3)   #=> ["prog:13"]

catch(symbol) {| | block } > obj

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 symbol. 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:

chomp => $_
chomp(string) => $_

Equivalent to $_ = $_.chomp(string). See String#chomp.

   $_ = "now\n"
   chomp         #=> "now"
   $_            #=> "now"
   chomp "ow"    #=> "n"
   $_            #=> "n"
   chomp "xxx"   #=> "n"
   $_            #=> "n"

chomp! => $_ or nil
chomp!(string) => $_ or nil

Equivalent to $_.chomp!(string). See String#chomp!

   $_ = "now\n"
   chomp!       #=> "now"
   $_           #=> "now"
   chomp! "x"   #=> nil
   $_           #=> "now"

chop => string

Equivalent to ($_.dup).chop!, except nil is never returned. See String#chop!.

   a  =  "now\r\n"
   $_ = a
   chop   #=> "now"
   $_     #=> "now"
   chop   #=> "no"
   chop   #=> "n"
   chop   #=> ""
   chop   #=> ""
   a      #=> "now\r\n"

chop! => $_ or nil

Equivalent to $_.chop!.

   a  = "now\r\n"
   $_ = a
   chop!   #=> "now"
   chop!   #=> "no"
   chop!   #=> "n"
   chop!   #=> ""
   chop!   #=> nil
   $_      #=> ""
   a       #=> ""

eval(string [, binding [, filename [,lineno]]]) => obj

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

   def getBinding(str)
     return binding
   end
   str = "hello"
   eval "str + ' Fred'"                      #=> "hello Fred"
   eval "str + ' Fred'", getBinding("bye")   #=> "bye Fred"

exec(command [, arg, ...])

Replaces the current process by running the given external command. If exec is given a single argument, that argument is taken as a line that is subject to shell expansion before being executed. If multiple arguments are given, the second and subsequent arguments are passed as parameters to command with no shell expansion. If the first argument is a two-element array, 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 MSDOS environments, the command is executed in a subshell; otherwise, one of the exec(2) system calls is used, so the running command may inherit some of the environment of the original program (including open file descriptors).

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

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

exit(integer=0)
Kernel::exit(integer=0)
Process::exit(integer=0)

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.

   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

Process.exit!(fixnum=-1)

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

   Process.exit!(0)

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

Kernel.fork [{ block }] => fixnum or nil
Process.fork [{ block }] => fixnum or nil

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.

format(format_string [, arguments...] ) => string
sprintf(format_string [, arguments...] ) => string

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. 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 listed in the table at the end of this section. The flag characters are:

  Flag     | Applies to   | Meaning
  ---------+--------------+-----------------------------------------
  space    | bdeEfgGiouxX | Leave a space at the start of
           |              | positive numbers.
  ---------+--------------+-----------------------------------------
  (digit)$ | all          | Specifies the absolute argument number
           |              | for this field. Absolute and relative
           |              | argument numbers cannot be mixed in a
           |              | sprintf string.
  ---------+--------------+-----------------------------------------
   #       | beEfgGoxX    | Use an alternative format. For the
           |              | conversions `o', `x', `X', and `b',
           |              | prefix the result with ``0'', ``0x'', ``0X'',
           |              |  and ``0b'', respectively. For `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.
  ---------+--------------+-----------------------------------------
  +        | bdeEfgGiouxX | Add a leading plus sign to positive numbers.
  ---------+--------------+-----------------------------------------
  -        | all          | Left-justify the result of this conversion.
  ---------+--------------+-----------------------------------------
  0 (zero) | bdeEfgGiouxX | Pad with zeros, not spaces.
  ---------+--------------+-----------------------------------------
  *        | 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.

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. 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.)

The field types are:

    Field |  Conversion
    ------+--------------------------------------------------------------
      b   | Convert argument as a binary number.
      c   | Argument is the numeric code for a single character.
      d   | Convert argument as a decimal number.
      E   | Equivalent to `e', but uses an uppercase E to indicate
          | the exponent.
      e   | Convert floating point argument into exponential notation
          | with one digit before the decimal point. The precision
          | determines the number of fractional digits (defaulting to six).
      f   | Convert floating point argument as [-]ddd.ddd,
          |  where the precision determines the number of digits after
          | the decimal point.
      G   | Equivalent to `g', but use an uppercase `E' in exponent form.
      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 d.dddd form otherwise.
      i   | Identical to `d'.
      o   | Convert argument as an octal number.
      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.
      u   | Treat argument as an unsigned decimal number. Negative integers
          | are displayed as a 32 bit two's complement plus one for the
          | underlying architecture; that is, 2 ** 32 + n.  However, since
          | Ruby has no inherent limit on bits used to represent the
          | integer, this value is preceded by two dots (..) in order to
          | indicate a infinite number of leading sign bits.
      X   | Convert argument as a hexadecimal number using uppercase
          | letters. Negative numbers will be displayed with two
          | leading periods (representing an infinite string of
          | leading 'FF's.
      x   | Convert argument as a hexadecimal number.
          | Negative numbers will be displayed with two
          | leading periods (representing an infinite string of
          | leading 'ff's.

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)                        #=> "..4294967173"

getc()

obsolete

gets(separator=$/) => string or nil

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 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.

global_variables => array

Returns an array of the names of global variables.

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

gsub(pattern, replacement) => string
gsub(pattern) {|...| block } => string

Equivalent to $_.gsub…, except that $_ receives the modified result.

   $_ = "quick brown fox"
   gsub /[aeiou]/, '*'   #=> "q**ck br*wn f*x"
   $_                    #=> "q**ck br*wn f*x"

gsub!(pattern, replacement) => string or nil
gsub!(pattern) {|...| block } => string or nil

Equivalent to Kernel::gsub, except nil is returned if $_ is not modified.

   $_ = "quick brown fox"
   gsub! /cat/, '*'   #=> nil
   $_                 #=> "quick brown fox"

block_given? => true or false
iterator? => true or false

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"

proc { |...| block } => a_proc
lambda { |...| block } => a_proc

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

load(filename, wrap=false) => true

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.

local_variables => array

Returns the names of the current local variables.

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

loop {|| block }

Repeatedly executes the block.

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

StopIteration raised in the block breaks the loop.

obj.method_missing(symbol [, *args] ) => result

Invoked by Ruby when obj is sent a message it cannot handle. symbol is the symbol for the method called, and args are any arguments that were passed to it. By default, the interpreter raises an error when this method is called. However, it is possible to override the method to provide more dynamic behavior. The example below creates a class Roman, which responds to methods with names consisting of roman numerals, returning the corresponding integer values.

   class Roman
     def romanToInt(str)
       # ...
     end
     def method_missing(methId)
       str = methId.id2name
       romanToInt(str)
     end
   end

   r = Roman.new
   r.iv      #=> 4
   r.xxiii   #=> 23
   r.mm      #=> 2000

open(path [, mode [, perm]] ) => io or nil
open(path [, mode [, perm]] ) {|io| block } => obj

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’’). (See the table of valid modes on page 331.) If a file is being created, its initial permissions may be set using the integer third parameter.

If a block is specified, it will be invoked with the File object as a parameter, and the file 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 ``|’’ is a single minus sign, Ruby forks, and this subprocess is connected to the parent. In the subprocess, the open call returns nil. If the command is not ``-’’, the subprocess runs the command. If a block is associated with an open("|-") call, that block will be 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.

   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 I/O object:

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

produces:

   Got: in Child

p(obj, ...) => nil

For each object, directly writes obj.inspect followed by the current output record separator to the program‘s standard output.

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

produces:

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

pretty_inspect()

returns a pretty printed object as a string.

print(obj, ...) => nil

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 ($\) is not nil, it will be appended to the output. If no arguments are given, prints $_. 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

printf(io, string [, obj ... ] ) => nil
printf(string [, obj ... ] ) => nil

Equivalent to:

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

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

proc { |...| block } => a_proc
lambda { |...| block } => a_proc

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

putc(int) => int

Equivalent to:

  $stdout.putc(int)

puts(obj, ...) => nil

Equivalent to

    $stdout.puts(obj, ...)

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

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

rand(max=0) => number

Converts max to an integer using max1 = max.to_i.abs. If the result is zero, returns a pseudorandom floating point number greater than or equal to 0.0 and less than 1.0. Otherwise, returns a pseudorandom integer greater than or equal to zero and less than max1. Kernel::srand may be used to ensure repeatable sequences of random numbers between different runs of the program. Ruby currently uses a modified Mersenne Twister with a period of 2**19937-1.

   srand 1234                 #=> 0
   [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]
   [ rand(10), rand(1000) ]   #=> [6, 817]
   srand 1234                 #=> 1234
   [ rand,  rand ]            #=> [0.191519450163469, 0.49766366626136]

readline(separator=$/) => string

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

readlines(separator=$/) => array

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

require(string) => true or false

Ruby tries to load the library named string, returning true if successful. If the filename does not resolve to an absolute path, it will be searched for in the directories listed in $:. If the file has the extension ``.rb’’, it is loaded as a source file; if the extension is ``.so’’, ``.o’’, or ``.dll’’, or whatever the default shared library extension is 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. The name of the loaded feature is added to the array in $". A feature will not be loaded if it‘s name already appears in $". However, the file name is not converted to an absolute path, so that ``require ‘a’;require ’./a‘’’ will load a.rb twice.

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

scan(pattern) => array
scan(pattern) {|///| block } => $_

Equivalent to calling $_.scan. See String#scan.

IO.select(read_array
[, write_array
[, error_array
[, timeout]]] ) => array or nil

See Kernel#select.

set_trace_func(proc) => proc
set_trace_func(nil) => nil

Establishes proc as the handler for tracing, or disables tracing if the parameter is nil. proc takes up to six parameters: an event name, a filename, a line number, an object id, a binding, and the name of a class. proc is invoked whenever an event occurs. Events are: c-call (call a C-language routine), c-return (return from a C-language routine), call (call a Ruby method), class (start a class or module definition), end (finish a class or module definition), line (execute code on a new line), raise (raise an exception), and return (return from a Ruby method). Tracing is disabled within the context of proc.

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

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

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

sleep([duration]) => fixnum

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. Zero arguments causes sleep to sleep forever.

   Time.new    #=> Wed Apr 09 08:56:32 CDT 2003
   sleep 1.2   #=> 1
   Time.new    #=> Wed Apr 09 08:56:33 CDT 2003
   sleep 1.9   #=> 2
   Time.new    #=> Wed Apr 09 08:56:35 CDT 2003

split([pattern [, limit]]) => array

Equivalent to $_.split(pattern, limit). See String#split.

format(format_string [, arguments...] ) => string
sprintf(format_string [, arguments...] ) => string

  Flag     | Applies to   | Meaning
  ---------+--------------+-----------------------------------------
  space    | bdeEfgGiouxX | Leave a space at the start of
           |              | positive numbers.
  ---------+--------------+-----------------------------------------
  (digit)$ | all          | Specifies the absolute argument number
           |              | for this field. Absolute and relative
           |              | argument numbers cannot be mixed in a
           |              | sprintf string.
  ---------+--------------+-----------------------------------------
   #       | beEfgGoxX    | Use an alternative format. For the
           |              | conversions `o', `x', `X', and `b',
           |              | prefix the result with ``0'', ``0x'', ``0X'',
           |              |  and ``0b'', respectively. For `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.
  ---------+--------------+-----------------------------------------
  +        | bdeEfgGiouxX | Add a leading plus sign to positive numbers.
  ---------+--------------+-----------------------------------------
  -        | all          | Left-justify the result of this conversion.
  ---------+--------------+-----------------------------------------
  0 (zero) | bdeEfgGiouxX | Pad with zeros, not spaces.
  ---------+--------------+-----------------------------------------
  *        | 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.

The field types are:

    Field |  Conversion
    ------+--------------------------------------------------------------
      b   | Convert argument as a binary number.
      c   | Argument is the numeric code for a single character.
      d   | Convert argument as a decimal number.
      E   | Equivalent to `e', but uses an uppercase E to indicate
          | the exponent.
      e   | Convert floating point argument into exponential notation
          | with one digit before the decimal point. The precision
          | determines the number of fractional digits (defaulting to six).
      f   | Convert floating point argument as [-]ddd.ddd,
          |  where the precision determines the number of digits after
          | the decimal point.
      G   | Equivalent to `g', but use an uppercase `E' in exponent form.
      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 d.dddd form otherwise.
      i   | Identical to `d'.
      o   | Convert argument as an octal number.
      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.
      u   | Treat argument as an unsigned decimal number. Negative integers
          | are displayed as a 32 bit two's complement plus one for the
          | underlying architecture; that is, 2 ** 32 + n.  However, since
          | Ruby has no inherent limit on bits used to represent the
          | integer, this value is preceded by two dots (..) in order to
          | indicate a infinite number of leading sign bits.
      X   | Convert argument as a hexadecimal number using uppercase
          | letters. Negative numbers will be displayed with two
          | leading periods (representing an infinite string of
          | leading 'FF's.
      x   | Convert argument as a hexadecimal number.
          | Negative numbers will be displayed with two
          | leading periods (representing an infinite string of
          | leading 'ff's.

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)                        #=> "..4294967173"

srand(number=0) => old_seed

Seeds the pseudorandom number generator to the value of number.to_i.abs. If number is omitted, seeds the generator using a combination of the time, the process id, and a sequence number. (This is also the behavior if Kernel::rand is called without previously calling srand, but without the sequence.) By setting the seed to a known value, scripts can be made deterministic during testing. The previous seed value is returned. Also see Kernel::rand.

sub(pattern, replacement) => $_
sub(pattern) { block } => $_

Equivalent to $_.sub(args), except that $_ will be updated if substitution occurs.

sub!(pattern, replacement) => $_ or nil
sub!(pattern) {|...| block } => $_ or nil

Equivalent to $_.sub!(args).

syscall(fixnum [, args...]) => integer

Calls the operating system function identified by fixnum, passing in the arguments, which must be either String objects, or Integer objects that ultimately fit within a native long. Up to nine parameters may be passed (14 on the Atari-ST). The function identified by fixnum 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

system(cmd [, arg, ...]) => true or false

Executes cmd in a subshell, returning true if the command was found and ran successfully, false otherwise. An error status is available in $?. The arguments are processed in the same way as for Kernel::exec.

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

produces:

   config.h main.rb
   *

test(int_cmd, file1 [, file2] ) => obj

 Uses the integer <i>aCmd</i> to perform various tests on
 <i>file1</i> (first table below) or on <i>file1</i> and
 <i>file2</i> (second table).

 File tests on a single file:

   Test   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

throw(symbol [, obj])

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

trace_var(symbol, cmd ) => nil
trace_var(symbol) {|val| block } => nil

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

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

produces:

   $_ is now 'hello'
   $_ is now ' there'

Signal.trap( signal, proc ) => obj
Signal.trap( signal ) {| | block } => obj

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 operating system‘s default handler will be invoked. If the command is ``EXIT’’, the script will be terminated by the signal. 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

untrace_var(symbol [, cmd] ) => array or nil

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

warn(msg)

warn(msg) => nil

Display the given message (followed by a newline) on STDERR unless warnings are disabled (for example with the -W0 flag).

Methods

Instance

Instance Method Detail

Array(arg) => array

Float(arg) => float

Integer(arg) => integer

String(arg) => string

URI(uri_str)

__method__ => symbol

`cmd` => string

abort Kernel::abort Process::abort

at_exit { block } → proc

autoload(module, filename) => nil

autoload(module, filename) => nil

binding → a_binding

block_given? => true or false iterator? => true or false

callcc {|cont| block } => obj

caller(start=1) => array

catch(symbol) {| | block } > obj

chomp => $_ chomp(string) => $_

chomp! => $_ or nil chomp!(string) => $_ or nil

chop => string

chop! => $_ or nil

eval(string [, binding [, filename [,lineno]]]) => obj

exec(command [, arg, ...])

exit(integer=0) Kernel::exit(integer=0) Process::exit(integer=0)

Process.exit!(fixnum=-1)

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

Kernel.fork [{ block }] => fixnum or nil Process.fork [{ block }] => fixnum or nil

format(format_string [, arguments...] ) => string sprintf(format_string [, arguments...] ) => string

getc()

gets(separator=$/) => string or nil

global_variables => array

gsub(pattern, replacement) => string gsub(pattern) {|...| block } => string

gsub!(pattern, replacement) => string or nil gsub!(pattern) {|...| block } => string or nil

block_given? => true or false iterator? => true or false

proc { |...| block } => a_proc lambda { |...| block } => a_proc

load(filename, wrap=false) => true

local_variables => array

loop {|| block }

obj.method_missing(symbol [, *args] ) => result

open(path [, mode [, perm]] ) => io or nil open(path [, mode [, perm]] ) {|io| block } => obj

p(obj, ...) => nil

pretty_inspect()

print(obj, ...) => nil

printf(io, string [, obj ... ] ) => nil printf(string [, obj ... ] ) => nil

proc { |...| block } => a_proc lambda { |...| block } => a_proc

putc(int) => int

puts(obj, ...) => nil

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

rand(max=0) => number

readline(separator=$/) => string

readlines(separator=$/) => array

require(string) => true or false

scan(pattern) => array scan(pattern) {|///| block } => $_

IO.select(read_array [, write_array [, error_array [, timeout]]] ) => array or nil

set_trace_func(proc) => proc set_trace_func(nil) => nil

sleep([duration]) => fixnum

split([pattern [, limit]]) => array

format(format_string [, arguments...] ) => string sprintf(format_string [, arguments...] ) => string

srand(number=0) => old_seed

sub(pattern, replacement) => $_ sub(pattern) { block } => $_

sub!(pattern, replacement) => $_ or nil sub!(pattern) {|...| block } => $_ or nil

syscall(fixnum [, args...]) => integer

system(cmd [, arg, ...]) => true or false

test(int_cmd, file1 [, file2] ) => obj

throw(symbol [, obj])

trace_var(symbol, cmd ) => nil trace_var(symbol) {|val| block } => nil

Signal.trap( signal, proc ) => obj Signal.trap( signal ) {| | block } => obj

untrace_var(symbol [, cmd] ) => array or nil

warn(msg)

warn(msg) => nil

method => symbol

abort
Kernel::abort
Process::abort

block_given? => true or false
iterator? => true or false

chomp => $_
chomp(string) => $_

chomp! => $_ or nil
chomp!(string) => $_ or nil

exit(integer=0)
Kernel::exit(integer=0)
Process::exit(integer=0)

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

Kernel.fork [{ block }] => fixnum or nil
Process.fork [{ block }] => fixnum or nil

format(format_string [, arguments...] ) => string
sprintf(format_string [, arguments...] ) => string

gsub(pattern, replacement) => string
gsub(pattern) {|...| block } => string

gsub!(pattern, replacement) => string or nil
gsub!(pattern) {|...| block } => string or nil

block_given? => true or false
iterator? => true or false

proc { |...| block } => a_proc
lambda { |...| block } => a_proc

open(path [, mode [, perm]] ) => io or nil
open(path [, mode [, perm]] ) {|io| block } => obj

printf(io, string [, obj ... ] ) => nil
printf(string [, obj ... ] ) => nil

proc { |...| block } => a_proc
lambda { |...| block } => a_proc

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

scan(pattern) => array
scan(pattern) {|///| block } => $_

IO.select(read_array
[, write_array
[, error_array
[, timeout]]] ) => array or nil

set_trace_func(proc) => proc
set_trace_func(nil) => nil

format(format_string [, arguments...] ) => string
sprintf(format_string [, arguments...] ) => string

sub(pattern, replacement) => $_
sub(pattern) { block } => $_

sub!(pattern, replacement) => $_ or nil
sub!(pattern) {|...| block } => $_ or nil

trace_var(symbol, cmd ) => nil
trace_var(symbol) {|val| block } => nil

Signal.trap( signal, proc ) => obj
Signal.trap( signal ) {| | block } => obj