RUBY(1)                Ruby Programmer's Reference Guide               RUBY(1)

     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-ori-
     ented 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 declara-
             tions.  Variable names denote their scope - global, class, in-
             stance, 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 refer-
             enced 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 fea-
             tures 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 meth-
             ods, 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 facto-

     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 pro-
             grams 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 pro-

     Dynamic loading
             On most UNIX systems, you can load object files into the Ruby in-
             terpreter on-the-fly.

     Rich libraries
             In addition to the "builtin libraries" and "standard libraries"
             that are bundled with Ruby, a vast amount of third-party li-
             braries ("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.

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

     --copyright    Prints the copyright notice, and quits immediately without
                    running any script.

     --version      Prints the version of the Ruby interpreter, and quits im-
                    mediately without running any script.

     -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 encod-

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

     -I directory   Used to tell Ruby where to load the library scripts.  Di-
                    rectory 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 path-
                    name, 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

     -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 UTF-8.

     -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 executes
                          $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 output.

     --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

     --help         Prints a summary of the options.

     -i extension   Specifies in-place-edit mode.  The extension, if speci-
                    fied, 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-end-
                    ing 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 use-
                    ful when using -n or -p.

     -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 li-
                                       braries.  By default, Ruby will load
                                       the latest version of each installed
                                       gem. The Gem constant is true if
                                       RubyGems is enabled, false if other-

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

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

     --dump=target  Dump some information.

                    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 interpreter.


                          parsetree_with_comment AST nodes tree

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

                          insns   disassembled instructions

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

     --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 script arguments (script file
                    or -e options) are present, Ruby quits immediately.

     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


     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 vari-
                able 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 Ker-

     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 ob-
     ject heap of fixed-sized slots, while "malloc" refers to auxiliary allo-
     cations 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 di-
     vided 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.  Intro-
                                            duced 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, mini-
                                            mum: 1.0 (no growth)

     RUBY_GC_HEAP_GROWTH_MAX_SLOTS          Allocation rate is limited to this
                                            number of slots, preventing exces-
                                            sive allocation due to
                                            RUBY_GC_HEAP_GROWTH_FACTOR.  In-
                                            troduced 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 genera-
                                            tion 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 genera-
                                            tion allocation from malloc before
                                            GC starts.  Prevents excessive
                                            malloc growth due to RUBY_GC_MAL-
                                            LOC_LIMIT_GROWTH_FACTOR.  Intro-
                                            duced in Ruby 2.1, default: 32MB.

     RUBY_GC_MALLOC_LIMIT_GROWTH_FACTOR     Increases the limit of young gen-
                                            eration malloc calls, reducing GC
                                            frequency but increasing malloc
                                            growth until RUBY_GC_MAL-
                                            LOC_LIMIT_MAX is reached.  Intro-
                                            duced in Ruby 2.1, default: 1.4,
                                            minimum: 1.0 (no growth)

     RUBY_GC_OLDMALLOC_LIMIT                The initial limit of old genera-
                                            tion 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 genera-
                                            tion allocation from malloc before
                                            a full GC starts.  Prevents exces-
                                            sive malloc growth due to
                                            LOC_LIMIT_GROWTH_FACTOR.  Intro-
                                            duced in Ruby 2.1, default: 128MB

     RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR  Increases the limit of old genera-
                                            tion malloc allocation, reducing
                                            full GC frequency but increasing
                                            malloc growth until RUBY_GC_OLD-
                                            MALLOC_LIMIT_MAX is reached.  In-
                                            troduced 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 ap-
     plications 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

     RUBY_THREAD_MACHINE_STACK_SIZE  Machine stack size used at thread cre-
                                     ation.  default: 524288 or 1048575

     RUBY_FIBER_VM_STACK_SIZE        VM stack size used at fiber creation.
                                     default: 65536 or 131072

     RUBY_FIBER_MACHINE_STACK_SIZE   Machine stack size used at fiber cre-
                                     ation.  default: 262144 or 524288

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

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

     o   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 vulnerabili-
         ties immediately.

     Ruby is designed and implemented by Yukihiro Matsumoto <>.

     See <> for con-
     tributors to Ruby.

UNIX                            April 14, 2018                            UNIX
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