Module: Kernel
Relationships & Source Files | |
Extension / Inclusion / Inheritance Descendants | |
Included In:
| |
Defined in: | object.c, complex.c, cont.c, error.c, eval.c, eval_jump.c, file.c, io.c, load.c, object.c, proc.c, process.c, random.c, rational.c, ruby.c, signal.c, sprintf.c, variable.c, vm_backtrace.c, vm_eval.c, vm_trace.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"
Class Attribute Summary
-
block_given? ⇒ Boolean
readonly
Alias for .iterator?.
-
iterator? ⇒ Boolean
(also: .block_given?)
readonly
Returns
true
ifyield
would execute a block in the current context.
Class Method Summary
-
__callee__ ⇒ Symbol
Returns the called name of the current method as a ::Symbol.
-
__dir__ ⇒ String
Returns the canonicalized absolute path of the directory of the file from which this method is called.
-
__method__ ⇒ Symbol
Returns the name at the definition of the current method as a ::Symbol.
-
` ⇒ String
Returns the standard output of running cmd in a subshell.
-
abort
Terminate execution immediately, effectively by calling
Kernel.exit(false)
. -
Array(arg) ⇒ Array
Returns
arg
as an .Array. -
at_exit ⇒ 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.
- autoload(module, filename) ⇒ nil
-
autoload?(name) ⇒ String?
Returns filename to be loaded if name is registered as .autoload.
-
binding ⇒ Binding
Returns a ::Binding object, describing the variable and method bindings at the point of call.
-
callcc {|cont| ... } ⇒ Object
Generates a ::Continuation object, which it passes to the associated block.
-
caller(start = 1, length = nil) ⇒ Array?
Returns the current execution stack—an array containing strings in the form
file:line
orfile:line: in `method'
. -
caller_locations(start = 1, length = nil) ⇒ Array?
Returns the current execution stack—an array containing backtrace location objects.
-
catch([tag]) {|tag| ... } ⇒ Object
catch
executes its block. -
chomp ⇒ $_
Equivalent to
$_ = $_.chomp(string)
. -
chop ⇒ $_
Equivalent to
($_.dup).chop!
, exceptnil
is never returned. -
Complex(x[, y]) ⇒ Numeric
Returns x+i*y;.
-
eval(string [, binding [, filename [,lineno]]]) ⇒ Object
Evaluates the Ruby expression(s) in string.
-
exec([env,] command... [,options])
Replaces the current process by running the given external command, which can take one of the following forms:
-
exit(status = true)
Initiates the termination of the Ruby script by raising the ::SystemExit exception.
-
Process.exit!(status = false)
Exits the process immediately.
-
fail
(also: .raise)
With no arguments, raises the exception in
$!
or raises a ::RuntimeError if$!
isnil
. -
Float(arg) ⇒ Float
Returns arg converted to a float.
-
fork ⇒ Fixnum?
Creates a subprocess.
-
format(format_string [, arguments...] ) ⇒ String
(also: .sprintf)
Returns the string resulting from applying format_string to any additional arguments.
-
gets(sep = $/) ⇒ String?
Returns (and assigns to
$_
) the next line from the list of files in ARGV (or$*
), or from standard input if no files are present on the command line. -
global_variables ⇒ Array
Returns an array of the names of global variables.
-
gsub(pattern, replacement) ⇒ $_
Equivalent to
$_.gsub...
, except that$_
will be updated if substitution occurs. -
Hash(arg) ⇒ Hash
Converts arg to a
Hash
by calling arg.to_hash
. - Integer(arg, base = 0) ⇒ Integer
- lambda {|...| ... } ⇒ Proc
-
load(filename, wrap = false) ⇒ true
Loads and executes the Ruby program in the file filename.
-
local_variables ⇒ Array
Returns the names of the current local variables.
-
loop
Repeatedly executes the block.
-
open(path [, mode [, perm]] [, opt]) ⇒ IO?
Creates an ::IO object connected to the given stream, file, or subprocess.
-
p(obj) ⇒ Object
For each object, directly writes obj.
inspect
followed by a newline to the program's standard output. -
print(obj, ...) ⇒ nil
Prints each object in turn to
$stdout
. -
printf(io, string [, obj ... ]) ⇒ nil
Equivalent to:
-
proc {|...| ... } ⇒ Proc
Equivalent to Proc.new.
-
putc(int) ⇒ Integer
Equivalent to:
-
puts(obj, ...) ⇒ nil
Equivalent to.
-
raise
Alias for .fail.
-
rand(max = 0) ⇒ Numeric
If called without an argument, or if
max.to_i.abs == 0
, rand returns a pseudo-random floating point number between 0.0 and 1.0, including 0.0 and excluding 1.0. -
Rational(x[, y]) ⇒ Numeric
Returns x/y;.
-
readline(sep = $/) ⇒ String
Equivalent to .gets, except
readline
raises ::EOFError at end of file. -
readlines(sep = $/) ⇒ Array
Returns an array containing the lines returned by calling
Kernel.gets(sep)
until the end of file. -
require(name) ⇒ Boolean
Loads the given
name
, returningtrue
if successful andfalse
if the feature is already loaded. -
require_relative(string) ⇒ Boolean
Ruby tries to load the library named string relative to the requiring file's path.
-
IO.select(read_array [, write_array [, error_array [, timeout]]]) ⇒ Array?
Calls select(2) system call.
-
set_trace_func(proc) ⇒ Proc
Establishes proc as the handler for tracing, or disables tracing if the parameter is
nil
. -
sleep([duration]) ⇒ Fixnum
Suspends the current thread for duration seconds (which may be any number, including a .Float with fractional seconds).
-
spawn([env,] command... [,options]) ⇒ pid
spawn executes specified command and return its pid.
-
sprintf(format_string [, arguments...] ) ⇒ String
Alias for .format.
-
srand(number = Random.new_seed) ⇒ old_seed
Seeds the system pseudo-random number generator, Random::DEFAULT, with
number
. -
String(arg) ⇒ String
Returns arg as a
String
. -
sub(pattern, replacement) ⇒ $_
Equivalent to
$_.sub(args)
, except that$_
will be updated if substitution occurs. -
syscall(num [, args...]) ⇒ Integer
Calls the operating system function identified by num and returns the result of the function or raises ::SystemCallError if it failed.
-
system([env,] command... [,options]) ⇒ true, ...
Executes command… in a subshell.
-
test(cmd, file1 [, file2] ) ⇒ Object
Uses the character
cmd
to perform various tests onfile1
(first table below) or onfile1
andfile2
(second table). -
throw(tag [, obj])
Transfers control to the end of the active .catch block waiting for tag.
-
trace_var(symbol, cmd) ⇒ nil
Controls tracing of assignments to global variables.
-
Signal.trap(signal, command) ⇒ Object
Specifies the handling of signals.
-
untrace_var(symbol [, cmd] ) ⇒ Array?
Removes tracing for the specified command on the given global variable and returns
nil
. -
warn(msg, ...) ⇒ nil
Displays each of the given messages followed by a record separator on STDERR unless warnings have been disabled (for example with the
-W0
flag).
Class Attribute Details
block_given? ⇒ Boolean
(readonly)
iterator? ⇒ Boolean
Boolean
(readonly)
iterator? ⇒ Boolean
Alias for .iterator?.
block_given? ⇒ Boolean
(readonly)
iterator? ⇒ Boolean
Also known as: .block_given?
Boolean
(readonly)
iterator? ⇒ Boolean
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"
Class Method Details
__callee__ ⇒ Symbol
Returns the called name of the current method as a ::Symbol. If called outside of a method, it returns nil
.
__dir__ ⇒ String
Returns the canonicalized absolute path of the directory of the file from which this method is called. It means symlinks in the path is resolved. If __FILE__
is nil
, it returns nil
. The return value equals to File.dirname(File.realpath(__FILE__))
.
__method__ ⇒ Symbol
Returns the name at the definition of the current method as a ::Symbol. If called outside of a method, it returns nil
.
` ⇒ 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
abort([msg])
Process.abort([msg])
Terminate execution immediately, effectively by calling Kernel.exit(false)
. If msg is given, it is written to STDERR prior to terminating.
Array(arg) ⇒ Array
Returns arg
as an Array
.
First tries to call to_ary
on arg
, then to_a
.
Array(1..5) #=> [1, 2, 3, 4, 5]
at_exit ⇒ 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
autoload?(name) ⇒ String?
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)
binding
end
b = get_binding("hello")
eval("param", b) #=> "hello"
callcc {|cont| ... } ⇒ Object
Generates a ::Continuation object, which it passes to the associated block. You need to require 'continuation'
before using this method. Performing a cont.call
will cause the #callcc
to return (as will falling through the end of the block). The value returned by the #callcc
is the value of the block, or the value passed to cont.call
. See class ::Continuation for more details. Also see .throw for an alternative mechanism for unwinding a call stack.
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
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.
catch([tag]) {|tag| ... } ⇒ Object
catch
executes its block. If .throw is not called, the block executes normally, and catch
returns the value of the last expression evaluated.
catch(1) { 123 } # => 123
If throw(tag2, val)
is called, Ruby searches up its stack for a catch
block whose tag
has the same object_id
as tag2. When found, the block stops executing and returns val (or nil
if no second argument was given to .throw).
catch(1) { throw(1, 456) } # => 456
catch(1) { throw(1) } # => nil
When tag
is passed as the first argument, catch
yields it as the parameter of the block.
catch(1) {|x| x + 2 } # => 3
When no tag
is given, catch
yields a new unique object (as from Object.new
) as the block parameter. This object can then be used as the argument to .throw, and will match the correct catch
block.
catch do |obj_A|
catch do |obj_B|
throw(obj_B, 123)
puts "This puts is not reached"
end
puts "This puts is displayed"
456
end
# => 456
catch do |obj_A|
catch do |obj_B|
throw(obj_A, 123)
puts "This puts is still not reached"
end
puts "Now this puts is also not reached"
456
end
# => 123
chomp ⇒ $_
chomp(string) ⇒ $_
_
chomp(string) ⇒ $_
Equivalent to $_ = $_.chomp(string)
. See String#chomp. Available only when -p/-n command line option specified.
chop ⇒ $_
Equivalent to ($_.dup).chop!
, except nil
is never returned. See String#chop!. Available only when -p/-n command line option specified.
Complex(x[, y]) ⇒ Numeric
Returns x+i*y;
Complex(1, 2) #=> (1+2i)
Complex('1+2i') #=> (1+2i)
Complex(nil) #=> TypeError
Complex(1, nil) #=> TypeError
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.
eval(string [, binding [, filename [,lineno]]]) ⇒ Object
Evaluates the Ruby expression(s) in string. If binding is given, which must be a ::Binding object, the evaluation is performed in its context. If the optional filename and lineno parameters are present, they will be used when reporting syntax errors.
def get_binding(str)
return binding
end
str = "hello"
eval "str + ' Fred'" #=> "hello Fred"
eval "str + ' Fred'", get_binding("bye") #=> "bye Fred"
exec([env,] command... [,options])
Replaces the current process by running the given external command, which can take one of the following forms:
exec(commandline)
-
command line string which is passed to the standard shell
exec(cmdname, arg1, ...)
-
command name and one or more arguments (no shell)
exec([cmdname, argv0], arg1, ...)
-
command name, argv 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 .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
exit(status = true)
exit(status = true)
Process.exit(status = true)
Initiates the termination of the Ruby script by raising the ::SystemExit exception. This exception may be caught. The optional parameter is used to return a status code to the invoking environment. true
and FALSE of status means success and failure respectively. The interpretation of other integer values are system dependent.
begin
exit
puts "never get here"
rescue SystemExit
puts "rescued a SystemExit exception"
end
puts "after begin block"
produces:
rescued a SystemExit exception
after begin block
Just prior to termination, Ruby executes any .at_exit functions (see .at_exit) and runs any object finalizers (see ObjectSpace.define_finalizer).
at_exit { puts "at_exit function" }
ObjectSpace.define_finalizer("string", proc { puts "in finalizer" })
exit
produces:
at_exit function
in finalizer
Process.exit!(status = false)
raise
raise(string)
raise(exception [, string [, array]])
fail
fail(string)
fail(exception [, string [, array]])
Also known as: .raise
With no arguments, raises the exception in $!
or raises a ::RuntimeError if $!
is nil
. With a single .String argument, raises a ::RuntimeError with the string as a message. Otherwise, the first parameter should be 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
Float(arg) ⇒ Float
Returns arg converted to a float. ::Numeric types are converted directly, and with exception to string and nil the rest are converted using arg.to_f. Converting a string
with invalid characters will result in a ::ArgumentError. Converting nil
generates a ::TypeError.
Float(1) #=> 1.0
Float("123.456") #=> 123.456
Float("123.0_badstring") #=> ArgumentError: invalid value for Float(): "123.0_badstring"
Float(nil) #=> TypeError: can't convert nil into Float
Creates a subprocess. If a block is specified, that block is run in the subprocess, and the subprocess terminates with a status of zero. Otherwise, the fork
call returns twice, once in the parent, returning the process ID of the child, and once in the child, returning nil. The child process can exit using .exit! to avoid running any .at_exit functions. The parent process should use Process.wait to collect the termination statuses of its children or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.
The thread calling fork is the only thread in the created child process. fork doesn't copy other threads.
If fork is not usable, ::Process.respond_to?(:fork) returns false.
Note that fork(2) is not available on some platforms like Windows and NetBSD 4. Therefore you should use spawn() instead of fork().
Also known as: .sprintf
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, : => 2 })
#=> 1 : 2.000000
sprintf("%{foo}f", { :foo => 1 })
# => "1f"
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 $_
as an implicit parameter is gradually losing favor in the Ruby community.
global_variables ⇒ Array
Returns an array of the names of global variables.
global_variables.grep /std/ #=> [:$stdin, :$stdout, :$stderr]
gsub(pattern, replacement) ⇒ $_
gsub(pattern) {|...| ... } ⇒ $_
_
gsub(pattern) {|...| ... } ⇒ $_
Equivalent to $_.gsub...
, except that $_
will be updated if substitution occurs. Available only when -p/-n command line option specified.
Hash(arg) ⇒ Hash
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
Integer(arg, base = 0) ⇒ Integer
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 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 by first trying to_int
, then to_i
. Passing nil
raises a ::TypeError.
Integer(123.999) #=> 123
Integer("0x1a") #=> 26
Integer(Time.new) #=> 1204973019
Integer("0930", 10) #=> 930
Integer("111", 2) #=> 7
Integer(nil) #=> TypeError
lambda {|...| ... } ⇒ Proc
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
loop ⇒ Enumerator
Repeatedly executes the block.
If no block is given, an enumerator is returned instead.
loop do
print "Input: "
line = gets
break if !line or line =~ /^qQ/
# ...
end
::StopIteration raised in the block breaks the loop. In this case, loop returns the “result” value stored in the exception.
enum = Enumerator.new { |y|
y << "one"
y << "two"
:ok
}
result = loop {
puts enum.next
} #=> :ok
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
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
nil
printf(string [, obj ... ]) ⇒ nil
Equivalent to:
io.write(sprintf(string, obj, ...))
or
$stdout.write(sprintf(string, obj, ...))
proc {|...| ... } ⇒ Proc
Equivalent to Proc.new.
putc(int) ⇒ Integer
Equivalent to:
$stdout.putc(int)
Refer to the documentation for IO#putc for important information regarding multi-byte characters.
puts(obj, ...) ⇒ nil
Equivalent to
$stdout.puts(obj, ...)
raise
raise(string)
raise(exception [, string [, array]])
fail
fail(string)
fail(exception [, string [, array]])
Alias for .fail.
rand(max = 0) ⇒ Numeric
If called without an argument, or if max.to_i.abs == 0
, rand returns a pseudo-random floating point number between 0.0 and 1.0, including 0.0 and excluding 1.0.
rand #=> 0.2725926052826416
When max.abs
is greater than or equal to 1, rand
returns a pseudo-random integer greater than or equal to 0 and less than max.to_i.abs
.
rand(100) #=> 12
When max
is a ::Range, rand
returns a random number where range.member?(number) == true.
Negative or floating point values for max
are allowed, but may give surprising results.
rand(-100) # => 87
rand(-0.5) # => 0.8130921818028143
rand(1.9) # equivalent to rand(1), which is always 0
.srand may be used to ensure that sequences of random numbers are reproducible between different runs of a program.
See also Random.rand.
Rational(x[, y]) ⇒ Numeric
Returns x/y;
Rational(1, 2) #=> (1/2)
Rational('1/2') #=> (1/2)
Rational(nil) #=> TypeError
Rational(1, nil) #=> TypeError
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.
Equivalent to .gets, except readline
raises ::EOFError at end of file.
Returns an array containing the lines returned by calling Kernel.gets(sep)
until the end of file.
require(name) ⇒ Boolean
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.
require_relative(string) ⇒ Boolean
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.
IO.select(read_array [, write_array [, error_array [, timeout]]]) ⇒ Array?
Calls select(2) system call. It monitors given arrays of ::IO objects, waits until one or more of ::IO objects are 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.
IO.select peeks the buffer of ::IO objects for testing readability. If the ::IO buffer is not empty, IO.select immediately notifies readability. This “peek” only happens for ::IO objects. It does not happen for IO-like objects such as OpenSSL::SSL::SSLSocket
.
The best way to use IO.select is invoking it after nonblocking methods such as read_nonblock
, write_nonblock
, etc. The methods raise an exception which is extended by ::IO::WaitReadable or ::IO::WaitWritable. The modules notify how the caller should wait with IO.select. If ::IO::WaitReadable is raised, the caller should wait for reading. If ::IO::WaitWritable is raised, the caller should wait for writing.
So, blocking read (readpartial
) can be emulated using read_nonblock
and IO.select as follows:
begin
result = io_like.read_nonblock(maxlen)
rescue IO::WaitReadable
IO.select([io_like])
retry
rescue IO::WaitWritable
IO.select(nil, [io_like])
retry
end
Especially, the combination of nonblocking methods and IO.select is preferred for ::IO like objects such as OpenSSL::SSL::SSLSocket
. It has to_io
method to return underlying ::IO object. IO.select calls to_io
to obtain the file descriptor to wait.
This means that readability notified by IO.select doesn't mean readability from OpenSSL::SSL::SSLSocket
object.
The most likely situation is that OpenSSL::SSL::SSLSocket
buffers some data. IO.select doesn't see the buffer. So IO.select can block when OpenSSL::SSL::SSLSocket#readpartial
doesn't block.
However, several more complicated situations exist.
SSL is a protocol which is sequence of records. The record consists of multiple bytes. So, the remote side of SSL sends a partial record, IO.select notifies readability but OpenSSL::SSL::SSLSocket
cannot decrypt a byte and OpenSSL::SSL::SSLSocket#readpartial
will blocks.
Also, the remote side can request SSL renegotiation which forces the local SSL engine to write some data. This means OpenSSL::SSL::SSLSocket#readpartial
may invoke write
system call and it can block. In such a situation, OpenSSL::SSL::SSLSocket#read_nonblock
raises ::IO::WaitWritable instead of blocking. So, the caller should wait for ready for writability as above example.
The combination of nonblocking methods and IO.select is also useful for streams such as tty, pipe socket socket when multiple processes read from a stream.
Finally, Linux kernel developers don't guarantee that readability of select(2) means readability of following read(2) even for a single process. See select(2) manual on GNU/Linux system.
Invoking IO.select before IO#readpartial works well as usual. However it is not the best way to use IO.select.
The writability notified by select(2) doesn't show how many bytes writable. IO#write method blocks until given whole string is written. So, IO#write(two or more bytes)
can block after writability is notified by IO.select. IO#write_nonblock is required to avoid the blocking.
Blocking write (write
) can be emulated using write_nonblock
and IO.select as follows: ::IO::WaitReadable should also be rescued for SSL renegotiation in OpenSSL::SSL::SSLSocket
.
while 0 < string.bytesize
begin
written = io_like.write_nonblock(string)
rescue IO::WaitReadable
IO.select([io_like])
retry
rescue IO::WaitWritable
IO.select(nil, [io_like])
retry
end
string = string.byteslice(written..-1)
end
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 {
# IO.select follows IO#read. Not the best way to use IO.select.
rs, ws, = IO.select([rp], [wp])
if r = rs[0]
ret = r.read(5)
print ret
case ret
when /ping/
mesg = "pong\n"
when /pong/
mesg = "ping "
end
end
if w = ws[0]
w.write(mesg)
end
}
produces:
ping pong
ping pong
ping pong
(snipped)
ping
set_trace_func(proc) ⇒ Proc
set_trace_func(nil) ⇒ nil
nil
Establishes proc as the handler for tracing, or disables tracing if the parameter is nil
.
Note: this method is obsolete, please use ::TracePoint instead.
proc takes up to six parameters:
-
an event name
-
a filename
-
a line number
-
an object id
-
a binding
-
the name of a class
proc is invoked whenever an event occurs.
Events are:
c-call
-
call a C-language routine
c-return
-
return from a C-language routine
call
-
call a Ruby method
class
-
start a class or module definition),
end
-
finish a class or module definition),
line
-
execute code on a new line
- .raise
-
raise an exception
return
-
return from a Ruby method
Tracing is disabled within the context of proc.
class Test
def test
a = 1
b = 2
end
end
set_trace_func proc { |event, file, line, id, binding, classname|
printf "%8s %s:%-2d %10s %8s\n", event, file, line, id, classname
}
t = Test.new
t.test
line prog.rb:11 false
c-call prog.rb:11 new Class
c-call prog.rb:11 initialize Object
c-return prog.rb:11 initialize Object
c-return prog.rb:11 new Class
line prog.rb:12 false
call prog.rb:2 test Test
line prog.rb:3 test Test
line prog.rb:4 test Test
return prog.rb:4 test Test
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. 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
spawn([env,] command... [,options]) ⇒ pid
Process.spawn([env,] command... [,options]) ⇒ pid
pid
Process.spawn([env,] command... [,options]) ⇒ pid
spawn executes specified command and return its pid.
pid = spawn("tar xf ruby-2.0.0-p195.tar.bz2")
Process.wait pid
pid = spawn(RbConfig.ruby, "-eputs'Hello, world!'")
Process.wait pid
This method is similar to .system but it doesn't wait for the command to finish.
The parent process should use Process.wait to collect the termination status of its child or use Process.detach to register disinterest in their status; otherwise, the operating system may accumulate zombie processes.
spawn has bunch of options to specify process attributes:
env: hash
name => val : set the environment variable
name => nil : unset the environment variable
the keys and the values except for nil must be strings.
command...:
commandline : command line string which is passed to the standard shell
cmdname, arg1, ... : command name and one or more arguments (This form does not use the shell. See below for caveats.)
[cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)
options: hash
clearing environment variables:
:unsetenv_others => true : clear environment variables except specified by env
:unsetenv_others => false : don't clear (default)
process group:
:pgroup => true or 0 : make a new process group
:pgroup => pgid : join the specified process group
:pgroup => nil : don't change the process group (default)
create new process group: Windows only
:new_pgroup => true : the new process is the root process of a new process group
:new_pgroup => false : don't create a new process group (default)
resource limit: resourcename is core, cpu, data, etc. See Process.setrlimit.
:rlimit_resourcename => limit
:rlimit_resourcename => [cur_limit, max_limit]
umask:
:umask => int
redirection:
key:
FD : single file descriptor in child process
[FD, FD, ...] : multiple file descriptor in child process
value:
FD : redirect to the file descriptor in parent process
string : redirect to file with open(string, "r" or "w")
[string] : redirect to file with open(string, File::RDONLY)
[string, open_mode] : redirect to file with open(string, open_mode, 0644)
[string, open_mode, perm] : redirect to file with open(string, open_mode, perm)
[:child, FD] : redirect to the redirected file descriptor
:close : close the file descriptor in child process
FD is one of follows
:in : the file descriptor 0 which is the standard input
:out : the file descriptor 1 which is the standard output
:err : the file descriptor 2 which is the standard error
integer : the file descriptor of specified the integer
io : the file descriptor specified as io.fileno
file descriptor inheritance: close non-redirected non-standard fds (3, 4, 5, ...) or not
:close_others => 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, a positive integer, or nil. true and zero cause the process to be a process leader of a new process group. A non-zero positive integer causes the process to join the provided process group. The default value, nil, causes the process to remain in the same process group.
pid = spawn(command, :pgroup=>true) # process leader
pid = spawn(command, :pgroup=>10) # belongs to the process group 10
The :new_pgroup
key in options
specifies to pass CREATE_NEW_PROCESS_GROUP
flag to CreateProcessW()
that is Windows API. This option is only for Windows. true means the new process is the root process of the new process group. The new process has CTRL+C disabled. This flag is necessary for Process.kill(:SIGINT, pid)
on the subprocess. :new_pgroup
is false by default.
pid = spawn(command, :new_pgroup=>true) # new process group
pid = spawn(command, :new_pgroup=>false) # same process group
The :rlimit_
foo key specifies a resource limit. foo should be one of resource types such as core
. The corresponding value should be an integer or an array which have one or two integers: same as cur_limit and max_limit arguments for Process.setrlimit.
cur, max = Process.getrlimit(:CORE)
pid = spawn(command, :rlimit_core=>[0,max]) # disable core temporary.
pid = spawn(command, :rlimit_core=>max) # enable core dump
pid = spawn(command, :rlimit_core=>0) # never dump core.
The :umask
key in options
specifies the umask.
pid = spawn(command, :umask=>077)
The :in
, :out
, :err
, 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, [:out, :err]=>"/dev/null") # write mode
pid = spawn(command, 3=>"/dev/null") # read mode
For stdout and stderr (and combination of them), it is opened in write mode. Otherwise read mode is used.
For specifying flags and permission of file creation explicitly, an array is used instead.
pid = spawn(command, :in=>["file"]) # read mode is assumed
pid = spawn(command, :in=>["file", "r"])
pid = spawn(command, :out=>["log", "w"]) # 0644 assumed
pid = spawn(command, :out=>["log", "w", 0600])
pid = spawn(command, :out=>["log", File::WRONLY|File::EXCL|File::CREAT, 0600])
The array specifies a filename, flags and permission. The flags can be a string or an integer. If the flags is omitted or nil, File::RDONLY
is assumed. The permission should be an integer. If the permission is omitted or nil, 0644 is assumed.
If an array of IOs and integers are specified as a hash key, all the elements are redirected.
# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, [:out, :err]=>["log", "w"])
Another way to merge multiple file descriptors is [:child, fd]. [:child, fd] means the file descriptor in the child process. This is different from fd. For example, :err=>:out means redirecting child stderr to parent stdout. But :err=>[:child, :out] means redirecting child stderr to child stdout. They differ if stdout is redirected in the child process as follows.
# stdout and stderr is redirected to log file.
# The file "log" is opened just once.
pid = spawn(command, :out=>["log", "w"], :err=>[:child, :out])
[:child, :out] can be used to merge stderr into stdout in IO.popen. In this case, IO.popen redirects stdout to a pipe in the child process and [:child, :out] refers the redirected stdout.
io = IO.popen(["sh", "-c", "echo out; echo err >&2", :err=>[:child, :out]])
p io.read #=> "out\nerr\n"
The :chdir
key in options
specifies the current directory.
pid = spawn(command, :chdir=>"/var/tmp")
spawn closes all non-standard unspecified descriptors by default. The “standard” descriptors are 0, 1 and 2. This behavior is specified by :close_others
option. :close_others
doesn't affect the standard descriptors which are closed only if :close
is specified explicitly.
pid = spawn(command, :close_others=>true) # close 3,4,5,... (default)
pid = spawn(command, :close_others=>false) # don't close 3,4,5,...
:close_others
is 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 .exec for the standard shell.
Alias for .format.
srand(number = Random.new_seed) ⇒ old_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]
String(arg) ⇒ String
Returns arg as a String
.
First tries to call its to_str
method, then its to_s
method.
String(self) #=> "main"
String(self.class) #=> "Object"
String(123456) #=> "123456"
sub(pattern, replacement) ⇒ $_
sub(pattern) {|...| ... } ⇒ $_
_
sub(pattern) {|...| ... } ⇒ $_
Equivalent to $_.sub(args)
, except that $_
will be updated if substitution occurs. Available only when -p/-n command line option specified.
syscall(num [, args...]) ⇒ Integer
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. The DL (Fiddle) library is preferred for safer and a bit more portable programming.
system([env,] command... [,options]) ⇒ true
, ...
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 .spawn.
The hash arguments, env and options, are same as .exec and .spawn. See .spawn for details.
system("echo *")
system("echo", "*")
produces:
config.h main.rb
*
See .exec for the standard shell.
test(cmd, file1 [, file2] ) ⇒ Object
Uses the character cmd
to perform various tests on file1
(first table below) or on file1
and file2
(second table).
::File tests on a single file:
Cmd Returns Meaning
"A" | Time | Last access time for file1
"b" | boolean | True if file1 is a block device
"c" | boolean | True if file1 is a character device
"C" | Time | Last change time for file1
"d" | boolean | True if file1 exists and is a directory
"e" | boolean | True if file1 exists
"f" | boolean | True if file1 exists and is a regular file
"g" | boolean | True if file1 has the \CF{setgid} bit
| | set (false under NT)
"G" | boolean | True if file1 exists and has a group
| | ownership equal to the caller's group
"k" | boolean | True if file1 exists and has the sticky bit set
"l" | boolean | True if file1 exists and is a symbolic link
"M" | Time | Last modification time for file1
"o" | boolean | True if file1 exists and is owned by
| | the caller's effective uid
"O" | boolean | True if file1 exists and is owned by
| | the caller's real uid
"p" | boolean | True if file1 exists and is a fifo
"r" | boolean | True if file1 is readable by the effective
| | uid/gid of the caller
"R" | boolean | True if file is readable by the real
| | uid/gid of the caller
"s" | int/nil | If file1 has nonzero size, return the size,
| | otherwise return nil
"S" | boolean | True if file1 exists and is a socket
"u" | boolean | True if file1 has the setuid bit set
"w" | boolean | True if file1 exists and is writable by
| | the effective uid/gid
"W" | boolean | True if file1 exists and is writable by
| | the real uid/gid
"x" | boolean | True if file1 exists and is executable by
| | the effective uid/gid
"X" | boolean | True if file1 exists and is executable by
| | the real uid/gid
"z" | boolean | True if file1 exists and has a zero length
Tests that take two files:
"-" | boolean | True if file1 and file2 are identical
"=" | boolean | True if the modification times of file1
| | and file2 are equal
"<" | boolean | True if the modification time of file1
| | is prior to that of file2
">" | boolean | True if the modification time of file1
| | is after that of file2
throw(tag [, obj])
Transfers control to the end of the active .catch block waiting for tag. Raises ::UncaughtThrowError if there is no .catch block for the tag. The optional second parameter supplies a return value for the .catch block, which otherwise defaults to nil
. For examples, see .catch.
trace_var(symbol, cmd) ⇒ nil
trace_var(symbol) {|val| ... } ⇒ nil
nil
trace_var(symbol) {|val| ... } ⇒ nil
Controls tracing of assignments to global variables. The parameter symbol
identifies the variable (as either a string name or a symbol identifier). cmd (which may be a string or a ::Proc object) or block is executed whenever the variable is assigned. The block or ::Proc object receives the variable's new value as a parameter. Also see .untrace_var.
trace_var :$_, proc {|v| puts "$_ is now '#{v}'" }
$_ = "hello"
$_ = ' there'
produces:
$_ is now 'hello'
$_ is now ' there'
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
untrace_var(symbol [, cmd] ) ⇒ Array?
Removes tracing for the specified command on the given global variable and returns nil
. If no command is specified, removes all tracing for that variable and returns an array containing the commands actually removed.
warn(msg, ...) ⇒ nil
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