Kernel

Returns arg as an Array. First tries to call arg.to_ary, then arg.to_a.

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

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

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

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

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

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

Integer(123.999)    #=> 123
Integer("0x1a")     #=> 26
Integer(Time.new)   #=> 1204973019

 
               static VALUE
rb_f_integer(VALUE obj, VALUE arg)
{
    return rb_Integer(arg);
}
            

Converts arg to a String by calling its to_s method.

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

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

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

 
               static VALUE
rb_f_method_name(void)
{
    ID fname = rb_frame_caller(); /* need *caller* ID */

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

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

 
               static VALUE
rb_f_method_name(void)
{
    ID fname = rb_frame_caller(); /* need *caller* ID */

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

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

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

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

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

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

    return result;
}
            

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

 
               VALUE
rb_f_abort(int argc, VALUE *argv)
{
    extern void ruby_error_print(void);

    rb_secure(4);
    if (argc == 0) {
        if (!NIL_P(GET_THREAD()->errinfo)) {
            ruby_error_print();
        }
        rb_exit(EXIT_FAILURE);
    }
    else {
        VALUE args[2];

        rb_scan_args(argc, argv, "1", &args[1]);
        StringValue(argv[0]);
        rb_io_puts(argc, argv, rb_stderr);
        args[0] = INT2NUM(EXIT_FAILURE);
        rb_exc_raise(rb_class_new_instance(2, args, rb_eSystemExit));
    }
    return Qnil;                /* not reached */
}
            

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

 
               static VALUE
rb_f_at_exit(void)
{
    VALUE proc;

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

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

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

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

MISSING: documentation

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

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

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

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

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"

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

    if (cfp != 0 &&
        (cfp->lfp[0] & 0x02) == 0 &&
        GC_GUARDED_PTR_REF(cfp->lfp[0])) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
            

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

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

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

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

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

 
               static VALUE
rb_f_caller(int argc, VALUE *argv)
{
    VALUE level;
    int lev;

    rb_scan_args(argc, argv, "01", &level);

    if (NIL_P(level))
        lev = 1;
    else
        lev = NUM2INT(level);
    if (lev < 0)
        rb_raise(rb_eArgError, "negative level (%d)", lev);

    return vm_backtrace(GET_THREAD(), lev);
}
            

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

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

catch(:done) { routine(3) }

produces:

3
2
1
0

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

 
               static VALUE
rb_f_catch(int argc, VALUE *argv)
{
    VALUE tag;
    int state;
    volatile VALUE val = Qnil;          /* OK */
    rb_thread_t *th = GET_THREAD();
    rb_control_frame_t *saved_cfp = th->cfp;

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

    th->tag->tag = tag;

    if ((state = EXEC_TAG()) == 0) {
        val = rb_yield_0(1, &tag);
    }
    else if (state == TAG_THROW && RNODE(th->errinfo)->u1.value == tag) {
        th->cfp = saved_cfp;
        val = th->tag->retval;
        th->errinfo = Qnil;
        state = 0;
    }
    POP_TAG();
    if (state)
        JUMP_TAG(state);

    return val;
}
            

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

 
               static VALUE
rb_f_chomp(argc, argv)
    int argc;
    VALUE *argv;
{
    VALUE str = rb_funcall3(uscore_get(), rb_intern("chomp"), argc, argv);
    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.

 
               static VALUE
rb_f_chop()
{
    VALUE str = rb_funcall3(uscore_get(), rb_intern("chop"), 0, 0);
    rb_lastline_set(str);
    return str;
}
            

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

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

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

    rb_scan_args(argc, argv, "13", &src, &scope, &vfile, &vline);
    if (rb_safe_level() >= 4) {
        StringValue(src);
        if (!NIL_P(scope) && !OBJ_TAINTED(scope)) {
            rb_raise(rb_eSecurityError,
                     "Insecure: can't modify trusted binding");
        }
    }
    else {
        SafeStringValue(src);
    }
    if (argc >= 3) {
        StringValue(vfile);
    }
    if (argc >= 4) {
        line = NUM2INT(vline);
    }

    if (!NIL_P(vfile))
        file = RSTRING_PTR(vfile);
    return eval_string(self, src, scope, file, line);
}
            

Replaces the current process by running the given external command. If optional arguments, sequence of arg, are not given, that argument is taken as a line that is subject to shell expansion before being executed. If one or more arg given, they are passed as parameters to command with no shell expansion. If command is a two-element array, the first element is the command to be executed, and the second argument is used as the argv[0] value, which may show up in process listings. In order to execute the command, one of the exec(2) system calls is used, so the running command may inherit some of the environment of the original program (including open file descriptors).

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

Raises SystemCallError if the command couldn't execute (typically Errno::ENOENT when it was not found).

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

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

 
               VALUE
rb_f_exec(int argc, VALUE *argv)
{
    struct rb_exec_arg earg;

    rb_exec_arg_init(argc, argv, Qtrue, &earg);
    if (NIL_P(rb_ary_entry(earg.options, EXEC_OPTION_CLOSE_OTHERS)))
        rb_exec_arg_addopt(&earg, ID2SYM(rb_intern("close_others")), Qfalse);
    rb_exec_arg_fixup(&earg);

    rb_exec(&earg);
    rb_sys_fail(earg.prog);
    return Qnil;                /* dummy */
}
            

Initiates the termination of the Ruby script by raising the SystemExit exception. This exception may be caught. The optional parameter is used to return a status code to the invoking environment.

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

produces:

rescued a SystemExit exception
after begin block

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

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

produces:

at_exit function
in finalizer

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

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
        switch (status) {
          case Qtrue:
            istatus = EXIT_SUCCESS;
            break;
          case Qfalse:
            istatus = EXIT_FAILURE;
            break;
          default:
            istatus = NUM2INT(status);
#if EXIT_SUCCESS != 0
            if (istatus == 0)
                istatus = EXIT_SUCCESS;
#endif
            break;
        }
    }
    else {
        istatus = EXIT_SUCCESS;
    }
    rb_exit(istatus);
    return Qnil;                /* not reached */
}
            

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

Process.exit!(0)

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

    rb_secure(4);
    if (argc > 0 && rb_scan_args(argc, argv, "01", &status) == 1) {
        switch (status) {
          case Qtrue:
            istatus = EXIT_SUCCESS;
            break;
          case Qfalse:
            istatus = EXIT_FAILURE;
            break;
          default:
            istatus = NUM2INT(status);
            break;
        }
    }
    else {
        istatus = EXIT_FAILURE;
    }
    _exit(istatus);

    return Qnil;                /* not reached */
}
            

With no arguments, raises the exception in $! or raises a RuntimeError if $! is nil. With a single String argument, raises a RuntimeError with the string as a message. Otherwise, the first parameter should be the name of an Exception class (or an object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the rescue clause of begin...end blocks.

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

 
               static VALUE
rb_f_raise(int argc, VALUE *argv)
{
    VALUE err;
    if (argc == 0) {
        err = get_errinfo();
        if (!NIL_P(err)) {
            argc = 1;
            argv = &err;
        }
    }
    rb_raise_jump(rb_make_exception(argc, argv));
    return Qnil;                /* not reached */
}
            

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

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

 
               static VALUE
rb_f_fork(VALUE obj)
{
#if defined(HAVE_FORK) && !defined(CANNOT_FORK_WITH_PTHREAD)
    rb_pid_t pid;

    rb_secure(2);

    switch (pid = rb_fork(0, 0, 0, Qnil)) {
      case 0:
#ifdef linux
        after_exec();
#endif
        rb_thread_atfork();
        if (rb_block_given_p()) {
            int status;

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

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

      default:
        return PIDT2NUM(pid);
    }
#else
    rb_notimplement();
#endif
}
            

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

The syntax of a format sequence is follows.

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

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

The field type characters are:

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

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

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

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

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

Examples of flags:

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

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

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

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

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

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

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

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

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

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

Examples of width:

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

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

Examples of precisions:

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

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

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

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

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

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

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

Examples:

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

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

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.

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

Returns an array of the names of global variables.

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

 
               VALUE
rb_f_global_variables(void)
{
    VALUE ary = rb_ary_new();
    char buf[4];
    const char *s = "123456789";

    st_foreach_safe(rb_global_tbl, gvar_i, ary);
    while (*s) {
	sprintf(buf, "$%c", *s++);
	rb_ary_push(ary, ID2SYM(rb_intern(buf)));
    }
    return ary;
}
            

Equivalent to $_.gsub..., except that $_ receives the modified result. Available only when -p/-n command line option specified.

 
               static VALUE
rb_f_gsub(argc, argv)
    int argc;
    VALUE *argv;
{
    VALUE str = rb_funcall3(uscore_get(), rb_intern("gsub"), argc, argv);
    rb_lastline_set(str);
    return str;
}
            

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"

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

    if (cfp != 0 &&
        (cfp->lfp[0] & 0x02) == 0 &&
        GC_GUARDED_PTR_REF(cfp->lfp[0])) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}
            

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

 
               static VALUE
proc_lambda(void)
{
    return rb_block_lambda();
}
            

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

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

    rb_scan_args(argc, argv, "11", &fname, &wrap);
    rb_load(fname, RTEST(wrap));
    return Qtrue;
}
            

Returns the names of the current local variables.

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

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

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

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

Repeatedly executes the block.

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

StopIteration raised in the block breaks the loop.

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

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

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

The mode_enc is either a string or an integer. If it is an integer, it must be bitwise-or of open(2) flags, such as File::RDWR or File::EXCL. If it is a string, it is either “mode”, “mode:ext_enc”, or “mode:ext_enc:int_enc”. The mode is one of the following:

r: read (default)
w: write
a: append

The mode can be followed by “b” (means binary-mode), or “+” (means both reading and writing allowed) or both. If ext_enc (external encoding) is specified, read string will be tagged by the encoding in reading, and output string will be converted to the specified encoding in writing. If two encoding names, ext_enc and int_enc (external encoding and internal encoding), are specified, the read string is converted from ext_enc to int_enc then tagged with the int_enc in read mode, and in write mode, the output string will be converted from int_enc to ext_enc before writing.

If a file is being created, its initial permissions may be set using the integer third parameter.

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

If path starts with a pipe character, a subprocess is created, connected to the caller by a pair of pipes. The returned IO object may be used to write to the standard input and read from the standard output of this subprocess. If the command following the “|'' is a single minus sign, Ruby forks, and this subprocess is connected to the parent. In the subprocess, the open call returns nil. If the command is not “-'', the subprocess runs the command. If a block is associated with an open("|-") call, that block will be run twice—once in the parent and once in the child. The block parameter will be an IO object in the parent and nil in the child. The parent's IO object will be connected to the child's $stdin and $stdout. The subprocess will be terminated at the end of the block.

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

produces:

This is line one

Open a subprocess and read its output:

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

produces:

Wed Apr  9 08:56:31 CDT 2003

Open a subprocess running the same Ruby program:

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

produces:

Got: in Child

Open a subprocess using a block to receive the I/O object:

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

produces:

Got: in Child

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

    if (argc >= 1) {
        CONST_ID(to_open, "to_open");
        if (rb_respond_to(argv[0], to_open)) {
            redirect = Qtrue;
        }
        else {
            VALUE tmp = argv[0];
            FilePathValue(tmp);
            if (NIL_P(tmp)) {
                redirect = Qtrue;
            }
            else {
                VALUE cmd = check_pipe_command(tmp);
                if (!NIL_P(cmd)) {
                    argv[0] = cmd;
                    return rb_io_s_popen(argc, argv, rb_cIO);
                }
            }
        }
    }
    if (redirect) {
        VALUE io = rb_funcall2(argv[0], to_open, argc-1, argv+1);

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

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

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

produces:

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

 
               static VALUE
rb_f_p(int argc, VALUE *argv, VALUE self)
{
    int i;
    VALUE ret = Qnil;

    for (i=0; i<argc; i++) {
        rb_p(argv[i]);
    }
    if (argc == 1) {
        ret = argv[0];
    }
    else if (argc > 1) {
        ret = rb_ary_new4(argc, argv);
    }
    if (TYPE(rb_stdout) == T_FILE) {
        rb_io_flush(rb_stdout);
    }
    return ret;
}
            

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

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

produces:

cat12399
cat, 1, 2, 3, 99

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

Equivalent to:

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

or

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

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

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

    return Qnil;
}
            

Equivalent to Proc.new.

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

Equivalent to:

$stdout.putc(int)

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

Equivalent to

$stdout.puts(obj, ...)

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

With no arguments, raises the exception in $! or raises a RuntimeError if $! is nil. With a single String argument, raises a RuntimeError with the string as a message. Otherwise, the first parameter should be the name of an Exception class (or an object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the rescue clause of begin...end blocks.

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

 
               static VALUE
rb_f_raise(int argc, VALUE *argv)
{
    VALUE err;
    if (argc == 0) {
        err = get_errinfo();
        if (!NIL_P(err)) {
            argc = 1;
            argv = &err;
        }
    }
    rb_raise_jump(rb_make_exception(argc, argv));
    return Qnil;                /* not reached */
}
            

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

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

 
               static VALUE
rb_f_rand(int argc, VALUE *argv, VALUE obj)
{
    VALUE vmax;
    long val, max;
    struct MT *mt = &default_mt.mt;

    rb_scan_args(argc, argv, "01", &vmax);
    if (!genrand_initialized(mt)) {
        rand_srand(&default_mt, random_seed());
    }
    switch (TYPE(vmax)) {
      case T_FLOAT:
        if (RFLOAT_VALUE(vmax) <= LONG_MAX && RFLOAT_VALUE(vmax) >= LONG_MIN) {
            max = (long)RFLOAT_VALUE(vmax);
            break;
        }
        if (RFLOAT_VALUE(vmax) < 0)
            vmax = rb_dbl2big(-RFLOAT_VALUE(vmax));
        else
            vmax = rb_dbl2big(RFLOAT_VALUE(vmax));
        /* fall through */
      case T_BIGNUM:
      bignum:
        {
            struct RBignum *limit = (struct RBignum *)vmax;
            if (!RBIGNUM_SIGN(limit)) {
                limit = (struct RBignum *)rb_big_clone(vmax);
                RBIGNUM_SET_SIGN(limit, 1);
            }
            limit = (struct RBignum *)rb_big_minus((VALUE)limit, INT2FIX(1));
            if (FIXNUM_P((VALUE)limit)) {
                if (FIX2LONG((VALUE)limit) == -1)
                    return DBL2NUM(genrand_real(mt));
                return LONG2NUM(limited_rand(mt, FIX2LONG((VALUE)limit)));
            }
            return limited_big_rand(mt, limit);
        }
      case T_NIL:
        max = 0;
        break;
      default:
        vmax = rb_Integer(vmax);
        if (TYPE(vmax) == T_BIGNUM) goto bignum;
      case T_FIXNUM:
        max = FIX2LONG(vmax);
        break;
    }

    if (max == 0) {
        return DBL2NUM(genrand_real(mt));
    }
    if (max < 0) max = -max;
    val = limited_rand(mt, max-1);
    return LONG2NUM(val);
}
            

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

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

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

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

Ruby tries to load the library named string, returning true if successful. If the filename does not resolve to an absolute path, it will be searched for in the directories listed in $:. If the file has the extension “.rb'', it is loaded as a source file; if the extension is “.so'', “.o'', or “.dll'', or whatever the default shared library extension is on the current platform, Ruby loads the shared library as a Ruby extension. Otherwise, Ruby tries adding “.rb'', “.so'', and so on to the name. The name of the loaded feature is added to the array in $". A feature will not be loaded if its name already appears in $". The file name is converted to an absolute path, so “require 'a'; require './a''' will not load a.rb twice.

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

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

See Kernel#select.

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

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

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

#ifdef HAVE_RB_FD_INIT
    return rb_ensure(select_call, (VALUE)&args, select_end, (VALUE)&args);
#else
    return select_internal(args.read, args.write, args.except,
                           args.timeout, args.fdsets);
#endif

}
            

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

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

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

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

 
               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;
}
            

Suspends the current thread for duration seconds (which may be any number, including a Float with fractional seconds). Returns the actual number of seconds slept (rounded), which may be less than that asked for if another thread calls Thread#run. Zero arguments causes sleep to sleep forever.

Time.new    #=> 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

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

    beg = time(0);
    if (argc == 0) {
        rb_thread_sleep_forever();
    }
    else if (argc == 1) {
        rb_thread_wait_for(rb_time_interval(argv[0]));
    }
    else {
        rb_raise(rb_eArgError, "wrong number of arguments");
    }

    end = time(0) - beg;

    return INT2FIX(end);
}
            

Similar to Kernel::system except for not waiting for end of cmd, but returns its pid.

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

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

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

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

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

The :pgroup key in options specifies a process group. The corresponding value should be true, zero or positive integer. true and zero means the process should be a process leader. Other values specifies a process group to be belongs.

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

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

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

The :chdir key in options specifies the current directory.

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

The :umask key in options specifies the umask.

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

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

For example, stderr can be merged into stdout:

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

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

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

The standard output in the child process is not specified. So it is inherited from the parent process.

The standard input stream can be specifed by :in, STDIN and 0.

A filename can be specified as a hash value.

pid = spawn(command, STDIN=>"/dev/null") # read mode
pid = spawn(command, STDOUT=>"/dev/null") # write mode
pid = spawn(command, STDERR=>"log") # write mode
pid = spawn(command, 3=>"/dev/null") # read mode

For standard output and standard error, it is opened in write mode. Otherwise read mode is used.

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

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

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

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

# standard output and standard error is redirected to log file.
pid = spawn(command, [STDOUT, STDERR]=>["log", "w"])

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

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

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

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

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

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

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

It is also possible to exchange file descriptors.

pid = spawn(command, STDOUT=>STDERR, STDERR=>STDOUT)

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

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

    pid = rb_spawn(argc, argv);
    if (pid == -1) rb_sys_fail(RSTRING_PTR(argv[0]));
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    return PIDT2NUM(pid);
#else
    return Qnil;
#endif
}
            

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

The syntax of a format sequence is follows.

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

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

The field type characters are:

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

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

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

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

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

Examples of flags:

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

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

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

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

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

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

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

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

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

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

Examples of width:

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

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

Examples of precisions:

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

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

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

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

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

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

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

Examples:

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

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

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

 
               static VALUE
rb_f_srand(int argc, VALUE *argv, VALUE obj)
{
    VALUE seed;

    rb_secure(4);
    if (argc == 0) {
        seed = random_seed();
    }
    else {
        rb_scan_args(argc, argv, "01", &seed);
    }
    return rand_srand(&default_mt, seed);
}
            

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

 
               static VALUE
rb_f_sub(argc, argv)
    int argc;
    VALUE *argv;
{
    VALUE str = rb_funcall3(uscore_get(), rb_intern("sub"), argc, argv);
    rb_lastline_set(str);
    return str;
}
            

Calls the operating system function identified by fixnum, passing in the arguments, which must be either String objects, or Integer objects that ultimately fit within a native long. Up to nine parameters may be passed (14 on the Atari-ST). The function identified by fixnum is system dependent. On some Unix systems, the numbers may be obtained from a header file called syscall.h.

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

produces:

hello

 
               static VALUE
rb_f_syscall(int argc, VALUE *argv)
{
#if defined(HAVE_SYSCALL) && !defined(__CHECKER__)
#ifdef atarist
    unsigned long arg[14]; /* yes, we really need that many ! */
#else
    unsigned long arg[8];
#endif
    int retval = -1;
    int i = 1;
    int items = argc - 1;

    /* This probably won't work on machines where sizeof(long) != sizeof(int)
     * or where sizeof(long) != sizeof(char*).  But such machines will
     * not likely have syscall implemented either, so who cares?
     */

    rb_secure(2);
    if (argc == 0)
        rb_raise(rb_eArgError, "too few arguments for syscall");
    if (argc > sizeof(arg) / sizeof(arg[0]))
        rb_raise(rb_eArgError, "too many arguments for syscall");
    arg[0] = NUM2LONG(argv[0]); argv++;
    while (items--) {
        VALUE v = rb_check_string_type(*argv);

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

    switch (argc) {
      case 1:
        retval = syscall(arg[0]);
        break;
      case 2:
        retval = syscall(arg[0],arg[1]);
        break;
      case 3:
        retval = syscall(arg[0],arg[1],arg[2]);
        break;
      case 4:
        retval = syscall(arg[0],arg[1],arg[2],arg[3]);
        break;
      case 5:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4]);
        break;
      case 6:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5]);
        break;
      case 7:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6]);
        break;
      case 8:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7]);
        break;
#ifdef atarist
      case 9:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8]);
        break;
      case 10:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8], arg[9]);
        break;
      case 11:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8], arg[9], arg[10]);
        break;
      case 12:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8], arg[9], arg[10], arg[11]);
        break;
      case 13:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8], arg[9], arg[10], arg[11], arg[12]);
        break;
      case 14:
        retval = syscall(arg[0],arg[1],arg[2],arg[3],arg[4],arg[5],arg[6],
          arg[7], arg[8], arg[9], arg[10], arg[11], arg[12], arg[13]);
        break;
#endif /* atarist */
    }

    if (retval < 0) rb_sys_fail(0);
    return INT2NUM(retval);
#else
    rb_notimplement();
    return Qnil;                /* not reached */
#endif
}
            

Executes cmd in a subshell, returning true if the command gives zero exit status, false for non zero exit status. Returns nil if command execution fails. An error status is available in $?. The arguments are processed in the same way as for Kernel::exec.

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

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

produces:

config.h main.rb
*

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

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

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

    chfunc = signal(SIGCHLD, SIG_DFL);
#endif
    status = rb_spawn_internal(argc, argv, Qfalse);
#if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
    if (status > 0) {
        rb_syswait(status);
    }
#endif
#ifdef SIGCHLD
    signal(SIGCHLD, chfunc);
#endif
    if (status < 0) {
        return Qnil;
    }
    status = PST2INT(rb_last_status_get());
    if (status == EXIT_SUCCESS) return Qtrue;
    return Qfalse;
}
            

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

File tests on a single file:

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

Tests that take two files:

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

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

    if (argc == 0) rb_raise(rb_eArgError, "wrong number of arguments");
    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 'a':
          case 'e':
            return rb_file_exist_p(0, argv[1]);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        CHECK(1);
        if (rb_stat(fname, &st) == -1) {
            FilePathValue(fname);
            rb_sys_fail(RSTRING_PTR(fname));
        }

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

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

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

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

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

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

          case '<':
            if (st1.st_mtime < st2.st_mtime) return Qtrue;
            return Qfalse;
        }
    }
  unknown:
    /* unknown command */
    if (ISPRINT(cmd)) {
        rb_raise(rb_eArgError, "unknown command ?%c", cmd);
    }
    else {
        rb_raise(rb_eArgError, "unknown command ?\\x%02X", cmd);
    }
    return Qnil;                /* not reached */
}
            

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

 
               static VALUE
rb_f_throw(int argc, VALUE *argv)
{
    VALUE tag, value;
    rb_thread_t *th = GET_THREAD();
    struct rb_vm_tag *tt = th->tag;

    rb_scan_args(argc, argv, "11", &tag, &value);
    while (tt) {
        if (tt->tag == tag) {
            tt->retval = value;
            break;
        }
        tt = tt->prev;
    }
    if (!tt) {
        VALUE desc = rb_inspect(tag);
        rb_raise(rb_eArgError, "uncaught throw %s", RSTRING_PTR(desc));
    }
    rb_trap_restore_mask();
    th->errinfo = NEW_THROW_OBJECT(tag, 0, TAG_THROW);

    JUMP_TAG(TAG_THROW);
#ifndef __GNUC__
    return Qnil;                /* not reached */
#endif
}
            

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

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

produces:

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

 
               VALUE
rb_f_trace_var(int argc, VALUE *argv)
{
    VALUE var, cmd;
    struct global_entry *entry;
    struct trace_var *trace;

    rb_secure(4);
    if (rb_scan_args(argc, argv, "11", &var, &cmd) == 1) {
	cmd = rb_block_proc();
    }
    if (NIL_P(cmd)) {
	return rb_f_untrace_var(argc, argv);
    }
    entry = rb_global_entry(rb_to_id(var));
    if (OBJ_TAINTED(cmd)) {
	rb_raise(rb_eSecurityError, "Insecure: tainted variable trace");
    }
    trace = ALLOC(struct trace_var);
    trace->next = entry->var->trace;
    trace->func = rb_trace_eval;
    trace->data = cmd;
    trace->removed = 0;
    entry->var->trace = trace;

    return Qnil;
}
            

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

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

produces:

Terminating: 27461
Child died
Terminating: 27460

 
               static VALUE
sig_trap(int argc, VALUE *argv)
{
    struct trap_arg arg;

    rb_secure(2);
    if (argc == 0 || argc > 2) {
        rb_raise(rb_eArgError, "wrong number of arguments -- trap(sig, cmd)/trap(sig){...}");
    }

    arg.sig = trap_signm(argv[0]);
    if (argc == 1) {
        arg.cmd = rb_block_proc();
        arg.func = sighandler;
    }
    else if (argc == 2) {
        arg.cmd = argv[1];
        arg.func = trap_handler(&arg.cmd, arg.sig);
    }

    if (OBJ_TAINTED(arg.cmd)) {
        rb_raise(rb_eSecurityError, "Insecure: tainted signal trap");
    }
#if USE_TRAP_MASK
    /* disable interrupt */
# ifdef HAVE_SIGPROCMASK
    sigfillset(&arg.mask);
    sigprocmask(SIG_BLOCK, &arg.mask, &arg.mask);
# else
    arg.mask = sigblock(~0);
# endif

    return rb_ensure(trap, (VALUE)&arg, trap_ensure, (VALUE)&arg);
#else
    return trap(&arg);
#endif
}
            

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.

 
               VALUE
rb_f_untrace_var(int argc, VALUE *argv)
{
    VALUE var, cmd;
    ID id;
    struct global_entry *entry;
    struct trace_var *trace;
    st_data_t data;

    rb_secure(4);
    rb_scan_args(argc, argv, "11", &var, &cmd);
    id = rb_to_id(var);
    if (!st_lookup(rb_global_tbl, id, &data)) {
	rb_name_error(id, "undefined global variable %s", rb_id2name(id));
    }

    trace = (entry = (struct global_entry *)data)->var->trace;
    if (NIL_P(cmd)) {
	VALUE ary = rb_ary_new();

	while (trace) {
	    struct trace_var *next = trace->next;
	    rb_ary_push(ary, (VALUE)trace->data);
	    trace->removed = 1;
	    trace = next;
	}

	if (!entry->var->block_trace) remove_trace(entry->var);
	return ary;
    }
    else {
	while (trace) {
	    if (trace->data == cmd) {
		trace->removed = 1;
		if (!entry->var->block_trace) remove_trace(entry->var);
		return rb_ary_new3(1, cmd);
	    }
	    trace = trace->next;
	}
    }
    return Qnil;
}
            

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

 
               static VALUE
rb_warn_m(VALUE self, VALUE mesg)
{
    if (!NIL_P(ruby_verbose)) {
        rb_io_write(rb_stderr, mesg);
        rb_io_write(rb_stderr, rb_default_rs);
    }
    return Qnil;
}