Index:

Array Float Integer String ` (backquote) abort at_exit autoload binding block_given? callcc caller catch chomp chomp! chop chop! eval exec exit exit! fail fork format gets global_variables gsub gsub! iterator? lambda load local_variables loop open p print printf proc putc puts raise rand readline readlines require scan select set_trace_func singleton_method_added sleep split sprintf srand sub sub! syscall system test throw trace_var trap untrace_var

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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 beginning on page 351. This section documents the module methods. These methods are called without a receiver and thus can be called in functional form. Returns arg .to_a. Returns arg converted to a float. Numeric types are converted directly, nil is converted to 0.0, and the rest are converted using arg.to_f. 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. This behavior is different from that of String#to_i . Converts arg to a String by calling its to_s method. Returns the standard output of running cmd in a subshell. The built-in syntax %x{...} described on page 73 uses this method. Terminate execution immediately, effectively by calling Kernel.exit(1). 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. produces: Registers aFile to be loaded (using Kernel::require ) the first time that aModule (which may be a String or a symbol) is accessed. 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 Binding beginning on page 291. Returns true if yield would execute a block in the current context. 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 Continuation on page 294 for more details. Also see Kernel::throw for an alternative mechanism for unwinding a call stack. Returns the current execution stack---an array containing strings in the form ``file:line'' or ``file:line: in `method'''. The optional anInteger parameter determines the number of initial stack entries to omit from the result. catch executes its block. If a throw is executed, Ruby searches up its stack for a catch block with a tag corresponding to the throw's symbol. If found, that block is terminated, and catch returns the value given to throw. If throw is not called, the block terminates normally, and the value of catch is the value of the last expression evaluated. catch expressions may be nested, and the throw call need not be in lexical scope. produces: Equivalent to $_ = $_.chomp(aString). See String#chomp on page 367. Equivalent to $_.chomp!(aString). See String#chomp! Equivalent to ($_.dup).chop!, except nil is never returned. See String#chop! on page 367. Equivalent to $_.chop!. Evaluates the Ruby expression(s) in aString. If aBinding is given, the evaluation is performed in its context. The binding may be a Binding object or a Proc object. If the optional file and line parameters are present, they will be used when reporting syntax errors. Replaces the current process by running the given external command. If exec is given a single argument, that argument is taken as a line that is subject to shell expansion before being executed. If multiple arguments are given, the second and subsequent arguments are passed as parameters to command with no shell expansion. If the first argument is a two-element array, the first element is the command to be executed, and the second argument is used as the argv[0] value, which may show up in process listings. In MSDOS environments, the command is executed in a subshell; otherwise, one of the exec(2) system calls is used, so the running command may inherit some of the environment of the original program (including open file descriptors). 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. produces: Just prior to termination, Ruby executes any at_exit functions and runs any object finalizers (see ObjectSpace beginning on page 430). produces: Similar to Kernel::exit , but exception handling, at_exit functions, and finalizers are bypassed. Synonym for Kernel::raise . Creates a subshell. If a block is specified, that block is run in the subshell, and the subshell 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; otherwise, the operating system may accumulate zombie processes. produces: Synonym for Kernel::sprintf . Returns (and assigns to $_) the next line from the list of files in ARGV (or $*), or from standard input if no files are present on the command line. Returns nil at end of file. The optional argument specifies the record separator. The separator is included with the contents of each record. A separator of nil reads the entire contents, and a zero-length separator reads the input one paragraph at a time, where paragraphs are divided by two consecutive newlines. If multiple filenames are present in ARGV, gets(nil) will read the contents one file at a time. produces: Returns an array of the names of global variables. Equivalent to $_.gsub..., except that $_ receives the modified result. Equivalent to Kernel::gsub , except nil is returned if $_ is not modified. Synonym for Kernel::block_given? . The iterator? method will be removed in Ruby 1.8. Synonym for Kernel::proc . Loads and executes the Ruby program in the file aFileName. 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. Any local variables in the loaded file will not be propagated to the loading environment. Returns the names of the current local variables. Repeatedly executes the block. Creates an IO object connected to the given stream, file, or subprocess. If aString does not start with a pipe character (``|''), treat it as the name of a file to open using the specified mode defaulting to ``r'' (see the table of valid modes on page 326). 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 always returns nil in this case. If aString 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. produces: Open a subprocess and read its output: produces: Open a subprocess running the same Ruby program: produces: Open a subprocess using a block to receive the I/O object: produces: For each object, directly writes anObject.inspect followed by the current output record separator to the program's standard output. p bypasses the Ruby I/O libraries. produces: Prints each object in turn to $defout. If the output field separator (,ƒhƒ‹) is not nil, its contents will appear between each field. If the output record separator ($\) 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. produces: Equivalent to: anIO. write sprintf( aString, anObject ...)
or
$defout.write sprintf( aString, anObject ...) Creates a new procedure object from the given block. Equivalent to Proc.new . Equivalent to $defout.putc( anInteger ). Equivalent to $defout.puts( args ). 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 when sent exception). 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. 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. Equivalent to Kernel::gets , except readline raises EOFError at end of file. Returns an array containing the lines returned by calling Kernel.gets(aString) until the end of file. Ruby tries to load the library named aString, returning true if successful. If the filename does not resolve to an absolute path, it will be searched for in the directories listed in $:. If the file has the extension ``.rb'', it is loaded as a source file; if the extension is ``.so'', ``.o'', or ``.dll'',[Or whatever the default shared library extension is on the current platform.] Ruby loads the shared library as a Ruby extension. Otherwise, Ruby tries adding ``.rb'', ``.so'', and so on to the name. The name of the loaded feature is added to the array in $". A feature will not be loaded if it already appears in $". require returns true if the feature was successfully loaded. Equivalent to calling $_.scan. See String#scan on page 373. Performs a low-level select call, which waits for data to become available from input/output devices. The first three parameters are arrays of IO objects or nil. The last is a timeout in seconds, which should be an Integer or a Float. The call waits for data to become available for any of the IO objects in readArray, for buffers to have cleared sufficiently to enable writing to any of the devices in writeArray, or for an error to occur on the devices in errorArray. If one or more of these conditions are met, the call returns a three-element array containing arrays of the IO objects that were ready. Otherwise, if there is no change in status for timeout seconds, the call returns nil. If all parameters are nil, the current thread sleeps forever. Establishes aProc as the handler for tracing, or disables tracing if the parameter is nil. aProc takes up to six parameters: an event name, a filename, a line number, an object id, a binding, and the name of a class. aProc 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 aProc. See the example starting on page 267 for more information. Invoked with a symbol id whenever a singleton method is added to a module or a class. The default implementation in Kernel ignores this, but subclasses may override the method to provide specialized functionality. produces: Suspends the current thread for aNumber seconds (which may be a Float with fractional seconds). Returns the actual number of seconds slept (rounded), which may be less than that asked for if the thread was interrupted by a SIGALRM, or if another thread calls Thread#run . An argument of zero causes sleep to sleep forever. Equivalent to $_.split(pattern, limit). See String#split on page 374. Returns the string resulting from applying aFormatString to any additional arguments. Within the format string, any characters other than format sequences are copied to the result. A format sequence consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character. The field type controls how the corresponding sprintf argument is to be interpreted, while the flags modify that interpretation. The flag characters are shown in Table 23.1 on page 424, and the field type characters are listed in Table 23.2. The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field. For numeric fields, the precision controls the number of decimal places displayed. For string fields, the precision determines the maximum number of characters to be copied from the string. (Thus, the format sequence %10.10s will always contribute exactly ten characters to the result.) Seeds the pseudorandom number generator to the value of aNumber.to_i.abs. If aNumber 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 on page 421. Equivalent to $_.sub(args), except that $_ will be updated if substitution occurs. Equivalent to $_.sub!(args). Calls the operating system function identified by aFixnum, 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. produces: Executes aCmd in a subshell, returning true if the command was found and ran successfully, false otherwise. A detailed error code is available in $?. The arguments are processed in the same way as for Kernel::exec on page 415. produces: Uses the integer aCmd to perform various tests on file1 (Table 23.3 on page 426) or on file1 and file2 (Table 23.4). Transfers control to the end of the active catch block waiting for aSymbol. Raises NameError if there is no catch block for the symbol. The optional second parameter supplies a return value for the catch block, which otherwise defaults to nil. For examples, see Kernel::catch on page 413. Controls tracing of assignments to global variables. The parameter aSymbol 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 . produces: Specifies the handling of signals. The first parameter is a signal name (a string such as ``SIGALRM'', ``SIGUSR1'', and so on) or a signal number. The characters ``SIG'' may be omitted from the signal name. The command or block specifies code to be run when the signal is raised. If the command is the string ``IGNORE'' or ``SIG_IGN'', the signal will be ignored. If the command is ``DEFAULT'' or ``SIG_DFL'', the operating system's default handler will be invoked. If the command is ``EXIT'', the script will be terminated by the signal. Otherwise, the given command or block will be run. The special signal name ``EXIT'' or signal number zero will be invoked just prior to program termination. trap returns the previous handler for the given signal. produces: 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.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)). Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.