Provided by: ruby2.5_2.5.5-4ubuntu2_amd64 bug


     ruby — Interpreted object-oriented scripting language


     ruby [--copyright] [--version] [-SUacdlnpswvy] [-0[octal]] [-C directory]
          [-E external[:internal]] [-F[pattern]] [-I directory] [-K[c]] [-T[level]] [-W[level]]
          [-e command] [-i[extension]] [-r library] [-x[directory]] [--{enable|disable}-FEATURE]
          [--dump=target] [--verbose] [--] [program_file] [argument ...]


     Ruby is an interpreted scripting language for quick and easy object-oriented programming.
     It has many features to process text files and to do system management tasks (like in Perl).
     It is simple, straight-forward, and extensible.

     If you want a language for easy object-oriented programming, or you don't like the Perl
     ugliness, or you do like the concept of LISP, but don't like too many parentheses, Ruby
     might be your language of choice.


     Ruby's features are as follows:

             Ruby is an interpreted language, so you don't have to recompile programs written in
             Ruby to execute them.

     Variables have no type (dynamic typing)
             Variables in Ruby can contain data of any type.  You don't have to worry about
             variable typing.  Consequently, it has a weaker compile time check.

     No declaration needed
             You can use variables in your Ruby programs without any declarations.  Variable
             names denote their scope - global, class, instance, or local.

     Simple syntax
             Ruby has a simple syntax influenced slightly from Eiffel.

     No user-level memory management
             Ruby has automatic memory management.  Objects no longer referenced from anywhere
             are automatically collected by the garbage collector built into the interpreter.

     Everything is an object
             Ruby is a purely object-oriented language, and was so since its creation.  Even such
             basic data as integers are seen as objects.

     Class, inheritance, and methods
             Being an object-oriented language, Ruby naturally has basic features like classes,
             inheritance, and methods.

     Singleton methods
             Ruby has the ability to define methods for certain objects.  For example, you can
             define a press-button action for certain widget by defining a singleton method for
             the button.  Or, you can make up your own prototype based object system using
             singleton methods, if you want to.

     Mix-in by modules
             Ruby intentionally does not have the multiple inheritance as it is a source of
             confusion.  Instead, Ruby has the ability to share implementations across the
             inheritance tree.  This is often called a ‘Mix-in’.

             Ruby has iterators for loop abstraction.

             In Ruby, you can objectify the procedure.

     Text processing and regular expressions
             Ruby has a bunch of text processing features like in Perl.

     M17N, character set independent
             Ruby supports multilingualized programming. Easy to process texts written in many
             different natural languages and encoded in many different character encodings,
             without dependence on Unicode.

             With built-in bignums, you can for example calculate factorial(400).

     Reflection and domain specific languages
             Class is also an instance of the Class class. Definition of classes and methods is
             an expression just as 1+1 is. So your programs can even write and modify programs.
             Thus you can write your application in your own programming language on top of Ruby.

     Exception handling
             As in Java(tm).

     Direct access to the OS
             Ruby can use most UNIX system calls, often used in system programming.

     Dynamic loading
             On most UNIX systems, you can load object files into the Ruby interpreter on-the-

     Rich libraries
             In addition to the “builtin libraries” and “standard libraries” that are bundled
             with Ruby, a vast amount of third-party libraries (“gems”) are available via the
             package management system called ‘RubyGems’, namely the gem(1) command.  Visit
    ( to find the gems you need, and explore GitHub
             ( to see how they are being developed and used.


     Ruby interpreter accepts following command-line options (switches).  They are quite similar
     to those of perl(1).

     --copyright    Prints the copyright notice.

     --version      Prints the version of Ruby interpreter.

     -0[octal]      (The digit “zero”.)  Specifies the input record separator ($/) as an octal
                    number. If no digit is given, the null character is taken as the separator.
                    Other switches may follow the digits.  -00 turns Ruby into paragraph mode.
                    -0777 makes Ruby read whole file at once as a single string since there is no
                    legal character with that value.

     -C directory
     -X directory   Causes Ruby to switch to the directory.

     -E external[:internal]
     --encoding external[:internal]
                    Specifies the default value(s) for external encodings and internal encoding.
                    Values should be separated with colon (:).

                    You can omit the one for internal encodings, then the value
                    (Encoding.default_internal) will be nil.

                    Specify the default external or internal character encoding

     -F pattern     Specifies input field separator ($;).

     -I directory   Used to tell Ruby where to load the library scripts.  Directory path will be
                    added to the load-path variable ($:).

     -K kcode       Specifies KANJI (Japanese) encoding. The default value for script encodings
                    (__ENCODING__) and external encodings (Encoding.default_external) will be the
                    specified one. kcode can be one of

                          e       EUC-JP

                          s       Windows-31J (CP932)

                          u       UTF-8

                          n       ASCII-8BIT (BINARY)

     -S             Makes Ruby use the PATH environment variable to search for script, unless its
                    name begins with a slash.  This is used to emulate #! on machines that don't
                    support it, in the following manner:

                          #! /usr/local/bin/ruby
                          # This line makes the next one a comment in Ruby \
                            exec /usr/local/bin/ruby -S $0 $*

                    On some systems $0 does not always contain the full pathname, so you need the
                    -S switch to tell Ruby to search for the script if necessary (to handle
                    embedded spaces and such).  A better construct than $* would be ${1+"$@"},
                    but it does not work if the script is being interpreted by csh(1).

     -T[level=1]    Turns on taint checks at the specified level (default 1).

     -U             Sets the default value for internal encodings (Encoding.default_internal) to

     -W[level=2]    Turns on verbose mode at the specified level without printing the version
                    message at the beginning. The level can be;

                          0       Verbose mode is "silence". It sets the $VERBOSE to nil.

                          1       Verbose mode is "medium". It sets the $VERBOSE to false.

                          2 (default) Verbose mode is "verbose". It sets the $VERBOSE to true.
                                  -W2 is same as -w

     -a             Turns on auto-split mode when used with -n or -p.  In auto-split mode, Ruby
                          $F = $_.split
                    at beginning of each loop.

     -c             Causes Ruby to check the syntax of the script and exit without executing. If
                    there are no syntax errors, Ruby will print “Syntax OK” to the standard

     --debug        Turns on debug mode.  $DEBUG will be set to true.

     -e command     Specifies script from command-line while telling Ruby not to search the rest
                    of the arguments for a script file name.

     --help         Prints a summary of the options.

     -i extension   Specifies in-place-edit mode.  The extension, if specified, is added to old
                    file name to make a backup copy.  For example:

                          % echo matz > /tmp/junk
                          % cat /tmp/junk
                          % ruby -p -i.bak -e '$_.upcase!' /tmp/junk
                          % cat /tmp/junk
                          % cat /tmp/junk.bak

     -l             (The lowercase letter “ell”.)  Enables automatic line-ending processing,
                    which means to firstly set $\ to the value of $/, and secondly chops every
                    line read using chop!.

     -n             Causes Ruby to assume the following loop around your script, which makes it
                    iterate over file name arguments somewhat like sed -n or awk.

                          while gets

     -p             Acts mostly same as -n switch, but print the value of variable $_ at the each
                    end of the loop.  For example:

                          % echo matz | ruby -p -e '$! "a-z", "A-Z"'

     -r library     Causes Ruby to load the library using require.  It is useful when using -n or

     -s             Enables some switch parsing for switches after script name but before any
                    file name arguments (or before a --).  Any switches found there are removed
                    from ARGV and set the corresponding variable in the script.  For example:

                          #! /usr/local/bin/ruby -s
                          # prints "true" if invoked with `-xyz' switch.
                          print "true\n" if $xyz

     -v             Enables verbose mode.  Ruby will print its version at the beginning and set
                    the variable $VERBOSE to true.  Some methods print extra messages if this
                    variable is true.  If this switch is given, and no other switches are
                    present, Ruby quits after printing its version.

     -w             Enables verbose mode without printing version message at the beginning.  It
                    sets the $VERBOSE variable to true.

     -x[directory]  Tells Ruby that the script is embedded in a message.  Leading garbage will be
                    discarded until the first line that starts with “#!” and contains the string,
                    “ruby”.  Any meaningful switches on that line will be applied.  The end of
                    the script must be specified with either EOF, ^D (control-D), ^Z (control-Z),
                    or the reserved word __END__.  If the directory name is specified, Ruby will
                    switch to that directory before executing script.

     --yydebug      DO NOT USE.

                    Turns on compiler debug mode.  Ruby will print a bunch of internal state
                    messages during compilation.  Only specify this switch you are going to debug
                    the Ruby interpreter.

                    Disables (or enables) the specified FEATURE.
                    --enable-gems      Disables (or enables) RubyGems libraries.  By default,
                                       Ruby will load the latest version of each installed gem.
                                       The Gem constant is true if RubyGems is enabled, false if

                    --enable-rubyopt   Ignores (or considers) the RUBYOPT environment variable.
                                       By default, Ruby considers the variable.

                    --enable-all       Disables (or enables) all features.

     --dump=target  Dump some informations.

                    Prints the specified target.  target can be one of;

                          version version description same as --version

                          usage   brief usage message same as -h

                          help    Show long help message same as --help

                          syntax  check of syntax same as -c --yydebug

                          yydebug compiler debug mode, same as --yydebug

                                  Only specify this switch if you are going to debug the Ruby


                          parsetree_with_comment AST nodes tree

                                  Only specify this switch if you are going to debug the Ruby

                          insns   disassembled instructions

                                  Only specify this switch if you are going to debug the Ruby

     --verbose      Enables verbose mode without printing version message at the beginning.  It
                    sets the $VERBOSE variable to true.  If this switch is given, and no other
                    switches are present, Ruby quits after printing its version.


     RUBYLIB    A colon-separated list of directories that are added to Ruby's library load path
                ($:). Directories from this environment variable are searched before the standard
                load path is searched.


     RUBYOPT    Additional Ruby options.

                      RUBYOPT="-w -Ke"

                Note that RUBYOPT can contain only -d, -E, -I, -K, -r, -T, -U, -v, -w, -W,
                --debug, --disable-FEATURE and --enable-FEATURE.

     RUBYPATH   A colon-separated list of directories that Ruby searches for Ruby programs when
                the -S flag is specified.  This variable precedes the PATH environment variable.

     RUBYSHELL  The path to the system shell command.  This environment variable is enabled for
                only mswin32, mingw32, and OS/2 platforms.  If this variable is not defined, Ruby
                refers to COMSPEC.

     PATH       Ruby refers to the PATH environment variable on calling Kernel#system.

     And Ruby depends on some RubyGems related environment variables unless RubyGems is disabled.
     See the help of gem(1) as below.

           % gem help


     The Ruby garbage collector (GC) tracks objects in fixed-sized slots, but each object may
     have auxiliary memory allocations handled by the malloc family of C standard library calls (
     malloc(3), calloc(3), and realloc(3)).  In this documentatation, the "heap" refers to the
     Ruby object heap of fixed-sized slots, while "malloc" refers to auxiliary allocations
     commonly referred to as the "process heap".  Thus there are at least two possible ways to
     trigger GC:

           1       Reaching the object limit.

           2       Reaching the malloc limit.

     In Ruby 2.1, the generational GC was introduced and the limits are divided into young and
     old generations, providing two additional ways to trigger a GC:

           3       Reaching the old object limit.

           4       Reaching the old malloc limit.

     There are currently 4 possible areas where the GC may be tuned by the following 11
     environment variables:
     RUBY_GC_HEAP_INIT_SLOTS                Initial allocation slots.  Introduced in Ruby 2.1,
                                            default: 10000.

     RUBY_GC_HEAP_FREE_SLOTS                Prepare at least this amount of slots after GC.
                                            Allocate this number slots if there are not enough
                                            slots.  Introduced in Ruby 2.1, default: 4096

     RUBY_GC_HEAP_GROWTH_FACTOR             Increase allocation rate of heap slots by this
                                            factor.  Introduced in Ruby 2.1, default: 1.8,
                                            minimum: 1.0 (no growth)

     RUBY_GC_HEAP_GROWTH_MAX_SLOTS          Allocation rate is limited to this number of slots,
                                            preventing excessive allocation due to
                                            RUBY_GC_HEAP_GROWTH_FACTOR.  Introduced in Ruby 2.1,
                                            default: 0 (no limit)

     RUBY_GC_HEAP_OLDOBJECT_LIMIT_FACTOR    Perform a full GC when the number of old objects is
                                            more than R * N, where R is this factor and N is the
                                            number of old objects after the last full GC.
                                            Introduced in Ruby 2.1.1, default: 2.0

     RUBY_GC_MALLOC_LIMIT                   The initial limit of young generation allocation from
                                            the malloc-family.  GC will start when this limit is
                                            reached.  Default: 16MB

     RUBY_GC_MALLOC_LIMIT_MAX               The maximum limit of young generation allocation from
                                            malloc before GC starts.  Prevents excessive malloc
                                            growth due to RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR.
                                            Introduced in Ruby 2.1, default: 32MB.

     RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR     Increases the limit of young generation malloc calls,
                                            reducing GC frequency but increasing malloc growth
                                            until RUBY_GC_MALLOC_LIMIT_MAX is reached.
                                            Introduced in Ruby 2.1, default: 1.4, minimum: 1.0
                                            (no growth)

     RUBY_GC_OLDMALLOC_LIMIT                The initial limit of old generation allocation from
                                            malloc, a full GC will start when this limit is
                                            reached.  Introduced in Ruby 2.1, default: 16MB

     RUBY_GC_OLDMALLOC_LIMIT_MAX            The maximum limit of old generation allocation from
                                            malloc before a full GC starts.  Prevents excessive
                                            malloc growth due to
                                            RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR.  Introduced in
                                            Ruby 2.1, default: 128MB

     RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR  Increases the limit of old generation malloc
                                            allocation, reducing full GC frequency but increasing
                                            malloc growth until RUBY_GC_OLDMALLOC_LIMIT_MAX is
                                            reached.  Introduced in Ruby 2.1, default: 1.2,
                                            minimum: 1.0 (no growth)


     Stack size environment variables are implementation-dependent and subject to change with
     different versions of Ruby.  The VM stack is used for pure-Ruby code and managed by the
     virtual machine.  Machine stack is used by the operating system and its usage is dependent
     on C extensions as well as C compiler options.  Using lower values for these may allow
     applications to keep more Fibers or Threads running; but increases the chance of
     SystemStackError exceptions and segmentation faults (SIGSEGV).  These environment variables
     are available since Ruby 2.0.0.  All values are specified in bytes.

     RUBY_THREAD_VM_STACK_SIZE       VM stack size used at thread creation.  default: 131072
                                     (32-bit CPU) or 262144 (64-bit)

     RUBY_THREAD_MACHINE_STACK_SIZE  Machine stack size used at thread creation.  default: 524288
                                     or 1048575

     RUBY_FIBER_VM_STACK_SIZE        VM stack size used at fiber creation.  default: 65536 or

     RUBY_FIBER_MACHINE_STACK_SIZE   Machine stack size used at fiber creation.  default: 262144
                                     or 524288

SEE ALSO     The official web site.  Comprehensive catalog of Ruby libraries.


     ·   Security vulnerabilities should be reported via an email to
         Reported problems will be published after being fixed.

     ·   Other bugs and feature requests can be reported via the Ruby Issue Tracking System
         (  Do not report security vulnerabilities via this system
         because it publishes the vulnerabilities immediately.


     Ruby is designed and implemented by Yukihiro Matsumoto <>.

     See ⟨⟩ for contributors to Ruby.