module Kernel - Documentation for Ruby 4.0
Description: module Kernel: The Kernel module is included by class Object, so its methods are available in every Ruby object. The Kernel instance methods are documented in class
Keywords: ruby,module,Kernel

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# module Kernel

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

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

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

## What’s Here

Module Kernel provides methods that are useful for:

- Converting

- Querying

- Exiting

- Exceptions

- IO

- Procs

- Tracing

- Subprocesses

- Loading

- Yielding

- Random Values

- Other

### Converting

- `Array`: Returns an `Array` based on the given argument.

- `Complex`: Returns a `Complex` based on the given arguments.

- `Float`: Returns a `Float` based on the given arguments.

- `Hash`: Returns a `Hash` based on the given argument.

- `Integer`: Returns an `Integer` based on the given arguments.

- `Rational`: Returns a `Rational` based on the given arguments.

- `String`: Returns a `String` based on the given argument.

### Querying

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

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

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

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

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

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

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

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

- `class`: Returns the class of `self`.

- `frozen?`: Returns whether `self` is frozen.

- `global_variables`: Returns an array of global variables as symbols.

- `local_variables`: Returns an array of local variables as symbols.

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

### Exiting

- `abort`: Exits the current process after printing the given arguments.

- `at_exit`: Executes the given block when the process exits.

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

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

### Exceptions

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

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

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

### IO

- `::pp`: Prints the given objects in pretty form.

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

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

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

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

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

- `putc`: Equivalent to `$stdout.putc(object)` for the given object.

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

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

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

- `select`: Same as `IO.select`.

### Procs

- `lambda`: Returns a lambda proc for the given block.

- `proc`: Returns a new `Proc`; equivalent to `Proc.new`.

### Tracing

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

- `trace_var`: Starts tracing assignments to the given global variable.

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

### Subprocesses

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

- `exec`: Replaces current process with a new process.

- `fork`: Forks the current process into two processes.

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

- `system`: Executes the given command in a subshell.

### Loading

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

- `load`: Loads the given Ruby file.

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

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

### Yielding

- `tap`: Yields `self` to the given block; returns `self`.

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

### Random Values

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

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

### Other

- `eval`: Evaluates the given string as Ruby code.

- `loop`: Repeatedly executes the given block.

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

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

- `syscall`: Runs an operating system call.

- `trap`: Specifies the handling of system signals.

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

### Public Class Methods

Pathname (path)
Source

    # File pathname_builtin.rb, line 1167
    def Pathname(path) # :doc:
      return path if Pathname === path
      Pathname.new(path)
    end

Creates a `Pathname` object.

URI (uri)
Source

    # File lib/uri/common.rb, line 911
    def URI(uri)
      if uri.is_a?(URI::Generic)
        uri
      elsif uri = String.try_convert(uri)
        URI.parse(uri)
      else
        raise ArgumentError,
          "bad argument (expected URI object or URI string)"
      end
    end

Returns a URI object derived from the given `uri`, which may be a URI string or an existing URI object:

    require 'uri'
    # Returns a new URI.
    uri = URI('http://github.com/ruby/ruby')
    # => #<URI::HTTP http://github.com/ruby/ruby>
    # Returns the given URI.
    URI(uri)
    # => #<URI::HTTP http://github.com/ruby/ruby>

You must require ‘uri’ to use this method.

pp (*objs)
Source

    # File lib/pp.rb, line 731
    def pp(*objs)
      objs.each {|obj|
        PP.pp(obj)
      }
      objs.size <= 1 ? objs.first : objs
    end

prints arguments in pretty form.

`pp` returns argument(s).

### Public Instance Methods

__callee__ → symbol
Source

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

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

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

__dir__ → string
Source

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

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
Source

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

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

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

`command` → string
Source

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

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

        GetOpenFile(port, fptr);
        result = read_all(fptr, remain_size(fptr), Qnil);
        rb_io_close(port);
        rb_io_fptr_cleanup_all(fptr);
        RB_GC_GUARD(port);

        return result;
    }

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

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

Examples:

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

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

Array(object) → object or new_array
Source

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

Returns an array converted from `object`.

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

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

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

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

Complex(real, imag = 0, exception: true) → complex or nil
Complex(s, exception: true) → complex or nil
Source

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

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

Returns a new Complex object if the arguments are valid; otherwise raises an exception if `exception` is `true`; otherwise returns `nil`.

With `Numeric` arguments `real` and `imag`, returns `Complex.rect(real, imag)` if the arguments are valid.

With string argument `s`, returns a new Complex object if the argument is valid; the string may have:

- One or two numeric substrings, each of which specifies a `Complex`, `Float`, `Integer`, `Numeric`, or `Rational` value, specifying rectangular coordinates:

  - Sign-separated real and imaginary numeric substrings (with trailing character `'i'`):

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

  - Real-only numeric string (without trailing character `'i'`):

        Complex('1')  # => (1+0i)
        Complex('+1') # => (1+0i)
        Complex('-1') # => (-1+0i)

  - Imaginary-only numeric string (with trailing character `'i'`):

        Complex('1i')  # => (0+1i)
        Complex('+1i') # => (0+1i)
        Complex('-1i') # => (0-1i)

- At-sign separated real and imaginary rational substrings, each of which specifies a `Rational` value, specifying polar coordinates:

      Complex('1/2@3/4')   # => (0.36584443443691045+0.34081938001166706i)
      Complex('+1/2@+3/4') # => (0.36584443443691045+0.34081938001166706i)
      Complex('+1/2@-3/4') # => (0.36584443443691045-0.34081938001166706i)
      Complex('-1/2@+3/4') # => (-0.36584443443691045-0.34081938001166706i)
      Complex('-1/2@-3/4') # => (-0.36584443443691045+0.34081938001166706i)

Float(arg, exception: true) → float or nil
Source

    # File kernel.rb, line 194
    def Float(arg, exception: true)
      if Primitive.mandatory_only?
        Primitive.rb_f_float1(arg)
      else
        Primitive.rb_f_float(arg, exception)
      end
    end

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 an `ArgumentError`. Converting `nil` generates a `TypeError`. Exceptions can be suppressed by passing `exception: false`.

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

Hash(object) → object or new_hash
Source

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

Returns a hash converted from `object`.

- If `object` is:

  - A hash, returns `object`.

  - An empty array or `nil`, returns an empty hash.

- Otherwise, if `object.to_hash` returns a hash, returns that hash.

- Otherwise, returns `TypeError`.

Examples:

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

Integer(object, base = 0, exception: true) → integer or nil
Source

    # File kernel.rb, line 287
    def Integer(arg, base = 0, exception: true)
      if Primitive.mandatory_only?
        Primitive.rb_f_integer1(arg)
      else
        Primitive.rb_f_integer(arg, base, exception)
      end
    end

Returns an integer converted from `object`.

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

With a non-zero `base`, `object` must be a string or convertible to a string.

#### Numeric objects

With an integer argument `object` given, returns `object`:

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

With a floating-point argument `object` given, returns `object` truncated to an integer:

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

#### String objects

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

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

With `base` zero, string `object` may contain leading characters to specify the actual base (radix indicator):

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

With a positive `base` (in range 2..36) given, returns `object` converted to an integer in the given base:

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

With a negative `base` (in range -36..-2) given, returns `object` converted to the radix indicator if it exists or `base`:

    Integer('0x100', -2)   # => 256
    Integer('100', -2)     # => 4
    Integer('0b100', -8)   # => 4
    Integer('100', -8)     # => 64
    Integer('0o100', -10)  # => 64
    Integer('100', -10)    # => 100

`base` -1 is equivalent to the -10 case.

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

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

#### Other classes

Examples with `object` of various other classes:

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

#### Keywords

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

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

- Raises `TypeError` if `object` is `nil`.

- Raises `ArgumentError` if `object` is an invalid string.

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

Rational(x, y, exception: true) → rational or nil
Rational(arg, exception: true) → rational or nil
Source

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

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

Returns `x/y` or `arg` as a `Rational`.

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

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

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

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

Syntax of the string form:

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

See also `String#to_r`.

String(object) → object or new_string
Source

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

Returns a string converted from `object`.

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

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

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

abort
abort(msg = nil)
Source

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

Terminates execution immediately, effectively by calling `Kernel.exit(false)`.

If string argument `msg` is given, it is written to STDERR prior to termination; otherwise, if an exception was raised, prints its message and backtrace.

at_exit { block } → proc
Source

    static VALUE
    rb_f_at_exit(VALUE _)
    {
        VALUE proc;

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

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(const, filename) → nil
Source

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

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

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

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

Files that are currently being loaded must not be registered for autoload.

autoload?(name, inherit=true) → String or nil
Source

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

Returns filename to be loaded if name is registered as `autoload` in the current namespace or one of its ancestors.

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

    module C
      autoload(:D, "d")
      autoload?(:D)          #=> "d"
      autoload?(:B)          #=> nil
    end

    class E
      autoload(:F, "f")
      autoload?(:F)          #=> "f"
      autoload?(:B)          #=> "b"
    end

binding → a_binding
Source

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

Returns a `Binding` object, describing the variable and method bindings at the point of call. This object can be used when calling `Binding#eval` to execute the evaluated command in this environment, or extracting its local variables.

    class User
      def initialize(name, position)
        @name = name
        @position = position
      end

      def get_binding
        binding
      end
    end

    user = User.new('Joan', 'manager')
    template = '{name: @name, position: @position}'

    # evaluate template in context of the object
    eval(template, user.get_binding)
    #=> {:name=>"Joan", :position=>"manager"}

`Binding#local_variable_get` can be used to access the variables whose names are reserved Ruby keywords:

    # This is valid parameter declaration, but `if` parameter can't
    # be accessed by name, because it is a reserved word.
    def validate(field, validation, if: nil)
      condition = binding.local_variable_get('if')
      return unless condition

      # ...Some implementation ...
    end

    validate(:name, :empty?, if: false) # skips validation
    validate(:name, :empty?, if: true) # performs validation

block_given? → true or false
Source

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

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

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
Source

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

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

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 `Kernel#throw` for an alternative mechanism for unwinding a call stack.

caller(start=1, length=nil) → array or nil
caller(range) → array or nil
Source

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

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

caller_locations(start=1, length=nil) → array or nil
caller_locations(range) → array or nil
Source

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

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| block } → obj
Source

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

`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) → $_
Source

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

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

chop → $_
Source

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

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

class → class
Source

    # File kernel.rb, line 18
    def class
      Primitive.attr! :leaf
      Primitive.cexpr! 'rb_obj_class_must(self)'
    end

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

    1.class      #=> Integer
    self.class   #=> Object

clone(freeze: nil) → an_object
Source

    # File kernel.rb, line 47
    def clone(freeze: nil)
      Primitive.rb_obj_clone2(freeze)
    end

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

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

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

eval(string [, binding [, filename [,lineno]]]) → obj
Source

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

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

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

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

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_line, options = {})
exec([env, ] exe_path, *args, options = {})
Source

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

Replaces the current process by doing one of the following:

- Passing string `command_line` to the shell.

- Invoking the executable at `exe_path`.

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

The new process is created using the exec system call; it may inherit some of its environment from the calling program (possibly including open file descriptors).

Argument `env`, if given, is a hash that affects `ENV` for the new process; see Execution Environment.

Argument `options` is a hash of options for the new process; see Execution Options.

The first required argument is one of the following:

- `command_line` if it is a string, and if it begins with a shell reserved word or special built-in, or if it contains one or more meta characters.

- `exe_path` otherwise.

Argument `command_line`

String argument `command_line` is a command line to be passed to a shell; it must begin with a shell reserved word, begin with a special built-in, or contain meta characters:

    exec('if true; then echo "Foo"; fi') # Shell reserved word.
    exec('exit')                         # Built-in.
    exec('date > date.tmp')              # Contains meta character.

The command line may also contain arguments and options for the command:

    exec('echo "Foo"')

Output:

    Foo

See Execution Shell for details about the shell.

Raises an exception if the new process could not execute.

Argument `exe_path`

Argument `exe_path` is one of the following:

- The string path to an executable to be called.

- A 2-element array containing the path to an executable and the string to be used as the name of the executing process.

Example:

    exec('/usr/bin/date')

Output:

    Sat Aug 26 09:38:00 AM CDT 2023

Ruby invokes the executable directly. This form does not use the shell; see Arguments args for caveats.

    exec('doesnt_exist') # Raises Errno::ENOENT

If one or more `args` is given, each is an argument or option to be passed to the executable:

    exec('echo', 'C*')
    exec('echo', 'hello', 'world')

Output:

    C*
    hello world

Raises an exception if the new process could not execute.

exit(status = true)
exit(status = true)
Source

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

Initiates termination of the Ruby script by raising `SystemExit`; the exception may be caught. Returns exit status `status` to the underlying operating system.

Values `true` and `false` for argument `status` indicate, respectively, success and failure; The meanings of integer values are system-dependent.

Example:

    begin
      exit
      puts 'Never get here.'
    rescue SystemExit
      puts 'Rescued a SystemExit exception.'
    end
    puts 'After begin block.'

Output:

    Rescued a SystemExit exception.
    After begin block.

Just prior to final termination, Ruby executes any at-exit procedures (see Kernel::at_exit) and any object finalizers (see `ObjectSpace::define_finalizer`).

Example:

    at_exit { puts 'In at_exit function.' }
    ObjectSpace.define_finalizer('string', proc { puts 'In finalizer.' })
    exit

Output:

    In at_exit function.
    In finalizer.

exit!(status = false)
exit!(status = false)
Source

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

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

        UNREACHABLE_RETURN(Qnil);
    }

Exits the process immediately; no exit handlers are called. Returns exit status `status` to the underlying operating system.

    Process.exit!(true)

Values `true` and `false` for argument `status` indicate, respectively, success and failure; The meanings of integer values are system-dependent.

fail
Alias for: raise
fork { ... } → integer or nil
fork → integer or nil
Source

    static VALUE
    rb_f_fork(VALUE obj)
    {
        rb_pid_t pid;

        pid = rb_call_proc__fork();

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

        return PIDT2NUM(pid);
    }

Creates a child process.

With a block given, runs the block in the child process; on block exit, the child terminates with a status of zero:

    puts "Before the fork: #{Process.pid}"
    fork do
      puts "In the child process: #{Process.pid}"
    end                   # => 382141
    puts "After the fork: #{Process.pid}"

Output:

    Before the fork: 420496
    After the fork: 420496
    In the child process: 420520

With no block given, the `fork` call returns twice:

- Once in the parent process, returning the pid of the child process.

- Once in the child process, returning `nil`.

Example:

    puts "This is the first line before the fork (pid #{Process.pid})"
    puts fork
    puts "This is the second line after the fork (pid #{Process.pid})"

Output:

    This is the first line before the fork (pid 420199)
    420223
    This is the second line after the fork (pid 420199)

    This is the second line after the fork (pid 420223)

In either case, the child process may exit using `Kernel.exit!` to avoid the call to `Kernel#at_exit`.

To avoid zombie processes, the parent process should call either:

- `Process.wait`, to collect the termination statuses of its children.

- `Process.detach`, to register disinterest in their status.

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

Note that method `fork` is available on some platforms, but not on others:

    Process.respond_to?(:fork) # => true # Would be false on some.

If not, you may use ::spawn instead of `fork`.

format
Alias for: sprintf
frozen? → true or false
Source

    # File kernel.rb, line 67
    def frozen?
      Primitive.attr! :leaf
      Primitive.cexpr! 'rb_obj_frozen_p(self)'
    end

Returns the freeze status of obj.

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

gets(sep=$/ [, getline_args]) → string or nil
gets(limit [, getline_args]) → string or nil
gets(sep, limit [, getline_args]) → string or nil
Source

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

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
Source

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

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

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

gsub(pattern, replacement) → $_
gsub(pattern) {|...| block } → $_
Source

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

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

iterator? → true or false
Source

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

Deprecated. Use block_given? instead.

lambda { |...| block } → a_proc
Source

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

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

load(filename, wrap=false) → true
Source

    static VALUE
    rb_f_load(int argc, VALUE *argv, VALUE _)
    {
        VALUE fname, wrap;
        rb_scan_args(argc, argv, "11", &fname, &wrap);
        return load_entrypoint_internal(fname, wrap);
    }

Loads and executes the Ruby program in the file filename.

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

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

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

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

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

local_variables → array
Source

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

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

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

Returns the names of the current local variables.

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

loop { block }
loop → an_enumerator
Source

    # File kernel.rb, line 161
    def loop
      Primitive.attr! :inline_block
      unless defined?(yield)
        return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_f_loop_size)'
      end

      begin
        while true
          yield
        end
      rescue StopIteration => e
        e.result
      end
    end

Repeatedly executes the block.

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

    loop do
      print "Input: "
      line = gets
      # break if q, Q is entered or EOF signal (Ctrl-D on Unix, Ctrl-Z on windows) is sent
      break if !line or line =~ /^q/i
      # ...
    end

A `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

open(path, mode = 'r', perm = 0666, **opts) → io or nil
open(path, mode = 'r', perm = 0666, **opts) {|io| ... } → obj
Source

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

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

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

Creates an `IO` object connected to the given file.

With no block given, file stream is returned:

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

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

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

Output:

    #<File:t.txt>

See `File.open` for details.

p(object) → obj
p(*objects) → array of objects
p → nil
Source

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

For each object `obj`, executes:

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

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

Examples:

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

Output:

    0..4
    [0..4, 0..4, 0..4]

`Kernel#p` is designed for debugging purposes. Ruby implementations may define `Kernel#p` to be uninterruptible in whole or in part. On CRuby, `Kernel#p`‘s writing of data is uninterruptible.

pretty_inspect ()
Source

    # File lib/pp.rb, line 724
    def pretty_inspect
      PP.pp(self, ''.dup)
    end

Returns a pretty printed object as a string.

See the `PP` module for more information.

print(*objects) → nil
Source

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

Equivalent to `$stdout.print(*objects)`, this method is the straightforward way to write to `$stdout`.

Writes the given objects to `$stdout`; returns `nil`. Appends the output record separator `$OUTPUT_RECORD_SEPARATOR` `$\`), if it is not `nil`.

With argument `objects` given, for each object:

- Converts via its method `to_s` if not a string.

- Writes to `stdout`.

- If not the last object, writes the output field separator `$OUTPUT_FIELD_SEPARATOR` (`$,` if it is not `nil`.

With default separators:

    objects = [0, 0.0, Rational(0, 1), Complex(0, 0), :zero, 'zero']
    $OUTPUT_RECORD_SEPARATOR
    $OUTPUT_FIELD_SEPARATOR
    print(*objects)

Output:

    nil
    nil
    00.00/10+0izerozero

With specified separators:

    $OUTPUT_RECORD_SEPARATOR = "\n"
    $OUTPUT_FIELD_SEPARATOR = ','
    print(*objects)

Output:

    0,0.0,0/1,0+0i,zero,zero

With no argument given, writes the content of `$_` (which is usually the most recent user input):

    gets  # Sets $_ to the most recent user input.
    print # Prints $_.

printf(format_string, *objects) → nil
printf(io, format_string, *objects) → nil
Source

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

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

        return Qnil;
    }

Equivalent to:

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

For details on `format_string`, see Format Specifications.

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

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

Output (on $stdout):

    0024         24 24.00#

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

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

Output (on $stderr):

    0024         24 24.00# => nil

With no arguments, does nothing.

proc { |...| block } → a_proc
Source

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

Equivalent to `Proc.new`.

putc(int) → int
Source

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

Equivalent to:

    $stdout.putc(int)

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

puts(*objects) → nil
Source

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

Equivalent to

    $stdout.puts(objects)

raise(exception, message = exception.to_s, backtrace = nil, cause: $!)
raise(message = nil, cause: $!)
Source

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

Raises an exception; see Exceptions.

Argument `exception` sets the class of the new exception; it should be class `Exception` or one of its subclasses (most commonly, `RuntimeError` or `StandardError`), or an instance of one of those classes:

    begin
      raise(StandardError)
    rescue => x
      p x.class
    end
    # => StandardError

Argument `message` sets the stored message in the new exception, which may be retrieved by method `Exception#message`; the message must be a string-convertible object or `nil`:

    begin
      raise(StandardError, 'Boom')
    rescue => x
      p x.message
    end
    # => "Boom"

If argument `message` is not given, the message is the exception class name.

See Messages.

Argument `backtrace` might be used to modify the backtrace of the new exception, as reported by `Exception#backtrace` and `Exception#backtrace_locations`; the backtrace must be an array of `Thread::Backtrace::Location`, an array of strings, a single string, or `nil`.

Using the array of `Thread::Backtrace::Location` instances is the most consistent option and should be preferred when possible. The necessary value might be obtained from `caller_locations`, or copied from `Exception#backtrace_locations` of another error:

    begin
      do_some_work()
    rescue ZeroDivisionError => ex
      raise(LogicalError, "You have an error in your math", ex.backtrace_locations)
    end

The ways, both `Exception#backtrace` and `Exception#backtrace_locations` of the raised error are set to the same backtrace.

When the desired stack of locations is not available and should be constructed from scratch, an array of strings or a singular string can be used. In this case, only `Exception#backtrace` is set:

    begin
      raise(StandardError, 'Boom', %w[dsl.rb:3 framework.rb:1])
    rescue => ex
      p ex.backtrace
      # => ["dsl.rb:3", "framework.rb:1"]
      p ex.backtrace_locations
      # => nil
    end

If argument `backtrace` is not given, the backtrace is set according to an array of `Thread::Backtrace::Location` objects, as derived from the call stack.

See Backtraces.

Keyword argument `cause` sets the stored cause in the new exception, which may be retrieved by method `Exception#cause`; the cause must be an exception object (`Exception` or one of its subclasses), or `nil`:

    begin
      raise(StandardError, cause: RuntimeError.new)
    rescue => x
      p x.cause
    end
    # => #<RuntimeError: RuntimeError>

If keyword argument `cause` is not given, the cause is the value of `$!`.

See Cause.

In the alternate calling sequence, where argument `exception` not given, raises a new exception of the class given by `$!`, or of class `RuntimeError` if `$!` is `nil`:

    begin
      raise
    rescue => x
      p x
    end
    # => RuntimeError

With argument `exception` not given, argument `message` and keyword argument `cause` may be given, but argument `backtrace` may not be given.

`cause` can not be given as an only argument.

Also aliased as: fail
rand(max=0) → number
Source

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

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

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

    rand        #=> 0.2725926052826416

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

    rand(100)   #=> 12

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

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

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

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

Related: `Random.rand`.

    rand(100.0)        # => 64 (Integer because max.to_i is 100)
    Random.rand(100.0) # => 30.315320967824523

readline(sep = $/, chomp: false) → string
readline(limit, chomp: false) → string
readline(sep, limit, chomp: false) → string
Source

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

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

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

Optional keyword argument `chomp` specifies whether line separators are to be omitted.

readlines(sep = $/, chomp: false, **enc_opts) → array
readlines(limit, chomp: false, **enc_opts) → array
readlines(sep, limit, chomp: false, **enc_opts) → array
Source

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

Returns an array containing the lines returned by calling `Kernel#gets` until the end-of-stream is reached; (see Line IO).

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

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

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

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

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

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

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

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

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

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

Optional keyword argument `chomp` specifies whether line separators are to be omitted:

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

Optional keyword arguments `enc_opts` specify encoding options; see Encoding options.

require_relative(string) → true or false
Source

    VALUE
    rb_f_require_relative(VALUE obj, VALUE fname)
    {
        return rb_require_relative_entrypoint(fname);
    }

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

select(read_ios, write_ios = [], error_ios = [], timeout = nil) → array or nil
Source

    static VALUE
    rb_f_select(int argc, VALUE *argv, VALUE obj)
    {
        VALUE scheduler = rb_fiber_scheduler_current();
        if (scheduler != Qnil) {
            // It's optionally supported.
            VALUE result = rb_fiber_scheduler_io_selectv(scheduler, argc, argv);
            if (!UNDEF_P(result)) return result;
        }

        VALUE timeout;
        struct select_args args;
        struct timeval timerec;
        int i;

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

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

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

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

Not implemented on all platforms.

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

Argument `timeout` is a numeric value (such as integer or float) timeout interval in seconds. `timeout` can also be `nil` or `Float::INFINITY`. `nil` and `Float::INFINITY` means no timeout.

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

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

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

- An array of the objects in `error_ios` have pending exceptions.

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

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

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

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

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

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

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

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

However, several more complicated situations exist.

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

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

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

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

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

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

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

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

Example:

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

Output:

    ping pong
    ping pong
    ping pong
    (snipped)
    ping

set_trace_func(proc) → proc
set_trace_func(nil) → nil
Source

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

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

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

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

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 string

- a filename string

- a line number

- a method name symbol, or nil

- a binding, or nil

- the class, module, or nil

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, class_or_module|
      printf "%8s %s:%-2d %16p %14p\n", event, file, line, id, class_or_module
    }
    t = Test.new
    t.test

Produces:

    c-return prog.rb:8   :set_trace_func         Kernel
        line prog.rb:11              nil            nil
      c-call prog.rb:11             :new          Class
      c-call prog.rb:11      :initialize    BasicObject
    c-return prog.rb:11      :initialize    BasicObject
    c-return prog.rb:11             :new          Class
        line prog.rb:12              nil            nil
        call prog.rb:2             :test           Test
        line prog.rb:3             :test           Test
        line prog.rb:4             :test           Test
      return prog.rb:5             :test           Test

sleep(secs = nil) → slept_secs
Source

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

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

        time_t end = time(0) - beg;

        return TIMET2NUM(end);
    }

Suspends execution of the current thread for the number of seconds specified by numeric argument `secs`, or forever if `secs` is `nil`; returns the integer number of seconds suspended (rounded).

    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_line, options = {}) → pid
spawn([env, ] exe_path, *args, options = {}) → pid
Source

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

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

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

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

Creates a new child process by doing one of the following in that process:

- Passing string `command_line` to the shell.

- Invoking the executable at `exe_path`.

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

Returns the process ID (pid) of the new process, without waiting for it to complete.

To avoid zombie processes, the parent process should call either:

- `Process.wait`, to collect the termination statuses of its children.

- `Process.detach`, to register disinterest in their status.

The new process is created using the exec system call; it may inherit some of its environment from the calling program (possibly including open file descriptors).

Argument `env`, if given, is a hash that affects `ENV` for the new process; see Execution Environment.

Argument `options` is a hash of options for the new process; see Execution Options.

The first required argument is one of the following:

- `command_line` if it is a string, and if it begins with a shell reserved word or special built-in, or if it contains one or more meta characters.

- `exe_path` otherwise.

Argument `command_line`

String argument `command_line` is a command line to be passed to a shell; it must begin with a shell reserved word, begin with a special built-in, or contain meta characters:

    spawn('if true; then echo "Foo"; fi') # => 798847 # Shell reserved word.
    Process.wait                          # => 798847
    spawn('exit')                         # => 798848 # Built-in.
    Process.wait                          # => 798848
    spawn('date > /tmp/date.tmp')         # => 798879 # Contains meta character.
    Process.wait                          # => 798849
    spawn('date > /nop/date.tmp')         # => 798882 # Issues error message.
    Process.wait                          # => 798882

The command line may also contain arguments and options for the command:

    spawn('echo "Foo"') # => 799031
    Process.wait        # => 799031

Output:

    Foo

See Execution Shell for details about the shell.

Raises an exception if the new process could not execute.

Argument `exe_path`

Argument `exe_path` is one of the following:

- The string path to an executable to be called.

- A 2-element array containing the path to an executable to be called, and the string to be used as the name of the executing process.

      spawn('/usr/bin/date') # Path to date on Unix-style system.
      Process.wait

  Output:

      Mon Aug 28 11:43:10 AM CDT 2023

Ruby invokes the executable directly. This form does not use the shell; see Arguments args for caveats.

If one or more `args` is given, each is an argument or option to be passed to the executable:

    spawn('echo', 'C*')             # => 799392
    Process.wait                    # => 799392
    spawn('echo', 'hello', 'world') # => 799393
    Process.wait                    # => 799393

Output:

    C*
    hello world

Raises an exception if the new process could not execute.

sprintf(format_string *objects) → string
Source

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

Returns the string resulting from formatting `objects` into `format_string`.

For details on `format_string`, see Format Specifications.

Also aliased as: format
srand(number = Random.new_seed) → old_seed
Source

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

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

        return old;
    }

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

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

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

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

sub(pattern, replacement) → $_
sub(pattern) {|...| block } → $_
Source

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

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

syscall(integer_callno, *arguments) → integer
Source

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

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

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

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

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

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

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

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

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

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

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

Not implemented on all platforms.

system([env, ] command_line, options = {}, exception: false) → true, false, or nil
system([env, ] exe_path, *args, options = {}, exception: false) → true, false, or nil
Source

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

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

        last_status_clear(th);

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

        if (pid > 0) {
            VALUE status = rb_process_status_wait(pid, 0);
            struct rb_process_status *data = rb_check_typeddata(status, &rb_process_status_type);
            // Set the last status:
            rb_obj_freeze(status);
            th->last_status = status;

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

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

            RB_GC_GUARD(status);
        }

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

Creates a new child process by doing one of the following in that process:

- Passing string `command_line` to the shell.

- Invoking the executable at `exe_path`.

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

Returns:

- `true` if the command exits with status zero.

- `false` if the exit status is a non-zero integer.

- `nil` if the command could not execute.

Raises an exception (instead of returning `false` or `nil`) if keyword argument `exception` is set to `true`.

Assigns the command’s error status to `$?`.

The new process is created using the system system call; it may inherit some of its environment from the calling program (possibly including open file descriptors).

Argument `env`, if given, is a hash that affects `ENV` for the new process; see Execution Environment.

Argument `options` is a hash of options for the new process; see Execution Options.

The first required argument is one of the following:

- `command_line` if it is a string, and if it begins with a shell reserved word or special built-in, or if it contains one or more meta characters.

- `exe_path` otherwise.

Argument `command_line`

String argument `command_line` is a command line to be passed to a shell; it must begin with a shell reserved word, begin with a special built-in, or contain meta characters:

    system('if true; then echo "Foo"; fi')          # => true  # Shell reserved word.
    system('exit')                                  # => true  # Built-in.
    system('date > /tmp/date.tmp')                  # => true  # Contains meta character.
    system('date > /nop/date.tmp')                  # => false
    system('date > /nop/date.tmp', exception: true) # Raises RuntimeError.

Assigns the command’s error status to `$?`:

    system('exit')                             # => true  # Built-in.
    $?                                         # => #<Process::Status: pid 640610 exit 0>
    system('date > /nop/date.tmp')             # => false
    $?                                         # => #<Process::Status: pid 640742 exit 2>

The command line may also contain arguments and options for the command:

    system('echo "Foo"') # => true

Output:

    Foo

See Execution Shell for details about the shell.

Raises an exception if the new process could not execute.

Argument `exe_path`

Argument `exe_path` is one of the following:

- The string path to an executable to be called.

- A 2-element array containing the path to an executable and the string to be used as the name of the executing process.

Example:

    system('/usr/bin/date') # => true # Path to date on Unix-style system.
    system('foo')           # => nil  # Command failed.

Output:

    Mon Aug 28 11:43:10 AM CDT 2023

Assigns the command’s error status to `$?`:

    system('/usr/bin/date') # => true
    $?                      # => #<Process::Status: pid 645605 exit 0>
    system('foo')           # => nil
    $?                      # => #<Process::Status: pid 645608 exit 127>

Ruby invokes the executable directly. This form does not use the shell; see Arguments args for caveats.

    system('doesnt_exist') # => nil

If one or more `args` is given, each is an argument or option to be passed to the executable:

    system('echo', 'C*')             # => true
    system('echo', 'hello', 'world') # => true

Output:

    C*
    hello world

Raises an exception if the new process could not execute.

tap {|x| block } → obj
Source

    # File kernel.rb, line 89
    def tap
      Primitive.attr! :inline_block
      yield(self)
      self
    end

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

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

test(char, path0, path1 = nil) → object
Source

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Performs a test on one or both of the filesystem entities at the given paths `path0` and `path1`:

- Each path `path0` or `path1` points to a file, directory, device, pipe, etc.

- Character `char` selects a specific test.

The tests:

- Each of these tests operates only on the entity at `path0`, and returns `true` or `false`; for a non-existent entity, returns `false` (does not raise exception):

  Character | Test
  --- | ---
  `'b'` | Whether the entity is a block device.
  `'c'` | Whether the entity is a character device.
  `'d'` | Whether the entity is a directory.
  `'e'` | Whether the entity is an existing entity.
  `'f'` | Whether the entity is an existing regular file.
  `'g'` | Whether the entity's setgid bit is set.
  `'G'` | Whether the entity's group ownership is equal to the caller's.
  `'k'` | Whether the entity's sticky bit is set.
  `'l'` | Whether the entity is a symbolic link.
  `'o'` | Whether the entity is owned by the caller's effective uid.
  `'O'` | Like `'o'`, but uses the real uid (not the effective uid).
  `'p'` | Whether the entity is a FIFO device (named pipe).
  `'r'` | Whether the entity is readable by the caller's effective uid/gid.
  `'R'` | Like `'r'`, but uses the real uid/gid (not the effective uid/gid).
  `'S'` | Whether the entity is a socket.
  `'u'` | Whether the entity's setuid bit is set.
  `'w'` | Whether the entity is writable by the caller's effective uid/gid.
  `'W'` | Like `'w'`, but uses the real uid/gid (not the effective uid/gid).
  `'x'` | Whether the entity is executable by the caller's effective uid/gid.
  `'X'` | Like `'x'`, but uses the real uid/gid (not the effective uid/git).
  `'z'` | Whether the entity exists and is of length zero.

- This test operates only on the entity at `path0`, and returns an integer size or `nil`:

  Character | Test
  --- | ---
  `'s'` | Returns positive integer size if the entity exists and has non-zero length, `nil` otherwise.

- Each of these tests operates only on the entity at `path0`, and returns a `Time` object; raises an exception if the entity does not exist:

  Character | Test
  --- | ---
  `'A'` | Last access time for the entity.
  `'C'` | Last change time for the entity.
  `'M'` | Last modification time for the entity.

- Each of these tests operates on the modification time (`mtime`) of each of the entities at `path0` and `path1`, and returns a `true` or `false`; returns `false` if either entity does not exist:

  Character | Test
  --- | ---
  `'<'` | Whether the `mtime` at `path0` is less than that at `path1`.
  `'='` | Whether the `mtime` at `path0` is equal to that at `path1`.
  `'>'` | Whether the `mtime` at `path0` is greater than that at `path1`.

- This test operates on the content of each of the entities at `path0` and `path1`, and returns a `true` or `false`; returns `false` if either entity does not exist:

  Character | Test
  --- | ---
  `'-'` | Whether the entities exist and are identical.

then {|x| block } → an_object
Source

    # File kernel.rb, line 121
    def then
      Primitive.attr! :inline_block
      unless defined?(yield)
        return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_obj_size)'
      end
      yield(self)
    end

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

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

A good use of `then` is value piping in method chains:

    require 'open-uri'
    require 'json'

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

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

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

Also aliased as: yield_self
throw(tag [, obj])
Source

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

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

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 Kernel::catch.

trace_var(symbol, cmd ) → nil
trace_var(symbol) {|val| block } → nil
Source

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

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'

trap(signal, command) → obj
trap(signal) { ... } → obj
Source

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

        rb_check_arity(argc, 1, 2);

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

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

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

        return trap(sig, func, cmd);
    }

Specifies the handling of signals. Returns the previous handler for the given signal.

Argument `signal` is a signal name (a string or symbol such as `SIGALRM` or `SIGUSR1`) or an integer signal number. When `signal` is a string or symbol, the leading characters `SIG` may be omitted.

Argument `command` or block provided specifies code to be run when the signal is raised.

Argument `command` may also be a string or symbol with the following special values:

- `IGNORE`, `SIG_IGN`: the signal will be ignored.

- `DEFAULT`, `SIG_DFL`: Ruby’s default handler will be invoked.

- `EXIT`: the process will be terminated by the signal.

- `SYSTEM_DEFAULT`: the operating system’s default handler will be invoked.

The special signal name `EXIT` or signal number zero will be invoked just prior to program termination:

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

Outputs:

    Terminating: 27461
    Child died
    Terminating: 27460

untrace_var(symbol [, cmd] ) → array or nil
Source

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

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(*msgs, uplevel: nil, category: nil) → nil
Source

    # File warning.rb, line 52
    def warn(*msgs, uplevel: nil, category: nil)
      if Primitive.cexpr!("NIL_P(category)")
        Primitive.rb_warn_m(msgs, uplevel, nil)
      elsif Warning[category = Primitive.cexpr!("rb_to_symbol_type(category)")]
        Primitive.rb_warn_m(msgs, uplevel, category)
      end
    end

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

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

produces:

    warning 1
    warning 2

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

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

    def bar
      foo
    end

    bar

produces:

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

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

:deprecated

  Used for warning for deprecated functionality that may be removed in the future.

:experimental

  Used for experimental features that may change in future releases.

:performance

  Used for warning about APIs or pattern that have negative performance impact

yield_self
Alias for: then

### Private Instance Methods

JSON (object, opts = nil)
Source

    # File ext/json/lib/json/common.rb, line 1139
    def JSON(object, opts = nil)
      JSON[object, opts]
    end

If object is string-like, parse the string and return the parsed result as a Ruby data structure. Otherwise, generate a `JSON` text from the Ruby data structure object and return it.

The opts argument is passed through to generate/parse respectively. See generate and parse for their documentation.

Pathname (path)
Source

    # File pathname_builtin.rb, line 1167
    def Pathname(path) # :doc:
      return path if Pathname === path
      Pathname.new(path)
    end

Creates a `Pathname` object.

URI (uri)
Source

    # File lib/uri/common.rb, line 911
    def URI(uri)
      if uri.is_a?(URI::Generic)
        uri
      elsif uri = String.try_convert(uri)
        URI.parse(uri)
      else
        raise ArgumentError,
          "bad argument (expected URI object or URI string)"
      end
    end

Returns a URI object derived from the given `uri`, which may be a URI string or an existing URI object:

    require 'uri'
    # Returns a new URI.
    uri = URI('http://github.com/ruby/ruby')
    # => #<URI::HTTP http://github.com/ruby/ruby>
    # Returns the given URI.
    URI(uri)
    # => #<URI::HTTP http://github.com/ruby/ruby>

You must require ‘uri’ to use this method.

gem (gem_name, *requirements)
Source

    # File lib/rubygems/core_ext/kernel_gem.rb, line 35
    def gem(gem_name, *requirements) # :doc:
      skip_list = (ENV["GEM_SKIP"] || "").split(/:/)
      raise Gem::LoadError, "skipping #{gem_name}" if skip_list.include? gem_name

      if gem_name.is_a? Gem::Dependency
        unless Gem::Deprecate.skip
          warn "#{Gem.location_of_caller.join ":"}:Warning: Kernel.gem no longer "\
            "accepts a Gem::Dependency object, please pass the name "\
            "and requirements directly"
        end

        requirements = gem_name.requirement
        gem_name = gem_name.name
      end

      dep = Gem::Dependency.new(gem_name, *requirements)

      loaded = Gem.loaded_specs[gem_name]

      return false if loaded && dep.matches_spec?(loaded)

      spec = dep.to_spec

      if spec
        if Gem::LOADED_SPECS_MUTEX.owned?
          spec.activate
        else
          Gem::LOADED_SPECS_MUTEX.synchronize { spec.activate }
        end
      end
    end

Use `Kernel#gem` to activate a specific version of `gem_name`.

`requirements` is a list of version requirements that the specified gem must match, most commonly “= example.version.number”. See `Gem::Requirement` for how to specify a version requirement.

If you will be activating the latest version of a gem, there is no need to call `Kernel#gem`, `Kernel#require` will do the right thing for you.

`Kernel#gem` returns true if the gem was activated, otherwise false. If the gem could not be found, didn’t match the version requirements, or a different version was already activated, an exception will be raised.

`Kernel#gem` should be called before any require statements (otherwise RubyGems may load a conflicting library version).

`Kernel#gem` only loads prerelease versions when prerelease `requirements` are given:

    gem 'rake', '>= 1.1.a', '< 2'

In older RubyGems versions, the environment variable GEM_SKIP could be used to skip activation of specified gems, for example to test out changes that haven’t been installed yet. Now RubyGems defers to -I and the RUBYLIB environment variable to skip activation of a gem.

Example:

    GEM_SKIP=libA:libB ruby -I../libA -I../libB ./mycode.rb

j (*objs)
Source

    # File ext/json/lib/json/common.rb, line 1105
    def j(*objs)
      if RUBY_VERSION >= "3.0"
        warn "Kernel#j is deprecated and will be removed in json 3.0.0", uplevel: 1, category: :deprecated
      else
        warn "Kernel#j is deprecated and will be removed in json 3.0.0", uplevel: 1
      end

      objs.each do |obj|
        puts JSON.generate(obj, :allow_nan => true, :max_nesting => false)
      end
      nil
    end

Outputs objs to STDOUT as `JSON` strings in the shortest form, that is in one line.

jj (*objs)
Source

    # File ext/json/lib/json/common.rb, line 1120
    def jj(*objs)
      if RUBY_VERSION >= "3.0"
        warn "Kernel#jj is deprecated and will be removed in json 3.0.0", uplevel: 1, category: :deprecated
      else
        warn "Kernel#jj is deprecated and will be removed in json 3.0.0", uplevel: 1
      end

      objs.each do |obj|
        puts JSON.pretty_generate(obj, :allow_nan => true, :max_nesting => false)
      end
      nil
    end

Outputs objs to STDOUT as `JSON` strings in a pretty format, with indentation and over many lines.

pp (*objs)
Source

    # File lib/pp.rb, line 731
    def pp(*objs)
      objs.each {|obj|
        PP.pp(obj)
      }
      objs.size <= 1 ? objs.first : objs
    end

prints arguments in pretty form.

`pp` returns argument(s).

require (path)
Source

    # File lib/rubygems/core_ext/kernel_require.rb, line 36
    def require(path) # :doc:
      return gem_original_require(path) unless Gem.discover_gems_on_require

      RUBYGEMS_ACTIVATION_MONITOR.synchronize do
        path = File.path(path)

        # If +path+ belongs to a default gem, we activate it and then go straight
        # to normal require

        if spec = Gem.find_default_spec(path)
          name = spec.name

          next if Gem.loaded_specs[name]

          # Ensure -I beats a default gem
          resolved_path = begin
            rp = nil
            load_path_check_index = Gem.load_path_insert_index - Gem.activated_gem_paths
            Gem.suffixes.find do |s|
              $LOAD_PATH[0...load_path_check_index].find do |lp|
                if File.symlink? lp # for backward compatibility
                  next
                end

                full_path = File.expand_path(File.join(lp, "#{path}#{s}"))
                rp = full_path if File.file?(full_path)
              end
            end
            rp
          end

          next if resolved_path

          Kernel.send(:gem, name, Gem::Requirement.default_prerelease)

          Gem.load_bundler_extensions(Gem.loaded_specs[name].version) if name == "bundler"

          next
        end

        # If there are no unresolved deps, then we can use just try
        # normal require handle loading a gem from the rescue below.

        if Gem::Specification.unresolved_deps.empty?
          next
        end

        # If +path+ is for a gem that has already been loaded, don't
        # bother trying to find it in an unresolved gem, just go straight
        # to normal require.
        #--
        # TODO request access to the C implementation of this to speed up RubyGems

        if Gem::Specification.find_active_stub_by_path(path)
          next
        end

        # Attempt to find +path+ in any unresolved gems...

        found_specs = Gem::Specification.find_in_unresolved path

        # If there are no directly unresolved gems, then try and find +path+
        # in any gems that are available via the currently unresolved gems.
        # For example, given:
        #
        #   a => b => c => d
        #
        # If a and b are currently active with c being unresolved and d.rb is
        # requested, then find_in_unresolved_tree will find d.rb in d because
        # it's a dependency of c.
        #
        if found_specs.empty?
          found_specs = Gem::Specification.find_in_unresolved_tree path

          found_specs.each(&:activate)

        # We found +path+ directly in an unresolved gem. Now we figure out, of
        # the possible found specs, which one we should activate.
        else

          # Check that all the found specs are just different
          # versions of the same gem
          names = found_specs.map(&:name).uniq

          if names.size > 1
            raise Gem::LoadError, "#{path} found in multiple gems: #{names.join ", "}"
          end

          # Ok, now find a gem that has no conflicts, starting
          # at the highest version.
          valid = found_specs.find {|s| !s.has_conflicts? }

          unless valid
            le = Gem::LoadError.new "unable to find a version of '#{names.first}' to activate"
            le.name = names.first
            raise le
          end

          valid.activate
        end
      end

      begin
        gem_original_require(path)
      rescue LoadError => load_error
        if load_error.path == path &&
           RUBYGEMS_ACTIVATION_MONITOR.synchronize { Gem.try_activate(path) }

          return gem_original_require(path)
        end

        raise load_error
      end
    end

When RubyGems is required, `Kernel#require` is replaced with our own which is capable of loading gems on demand.

When you call `require 'x'`, this is what happens:

- If the file can be loaded from the existing Ruby loadpath, it is.

- Otherwise, installed gems are searched for a file that matches. If it’s found in gem ‘y’, that gem is activated (added to the loadpath).

The normal `require` functionality of returning false if that file has already been loaded is preserved.

y (*objects)
Source

    # File ext/psych/lib/psych/y.rb, line 5
    def y *objects
      puts Psych.dump_stream(*objects)
    end

An alias for `Psych.dump_stream` meant to be used with IRB.