# man > ruby3.2(1)

[_RUBY_(1)](https://www.chedong.com/phpMan.php/man/RUBY/1/markdown)                           Ruby Programmer's Reference Guide                          [_RUBY_(1)](https://www.chedong.com/phpMan.php/man/RUBY/1/markdown)

## NAME
       ruby — Interpreted object-oriented scripting language

## SYNOPSIS
       **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_ _..._]

## DESCRIPTION
       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 ugli‐
       ness, or you do like the concept of LISP, but don't like too many parentheses, Ruby might  be
       your language of choice.

## FEATURES
       Ruby's features are as follows:

### Interpretive
               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  vari‐
               able 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 de‐
               fine  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 confu‐
               sion.   Instead, Ruby has the ability to share implementations across the inheritance
               tree.  This is often called a ‘Mix-in’.

### Iterators
               Ruby has iterators for loop abstraction.

### Closures
               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, with‐
               out dependence on Unicode.

### Bignums
               With built-in bignums, you can for example calculate [factorial(400)](https://www.chedong.com/phpMan.php/man/factorial/400/markdown).

### 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-fly.

### 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)](https://www.chedong.com/phpMan.php/man/gem/1/markdown) command.  Visit RubyGems.org
               (<https://rubygems.org/>)  to  find   the   gems   you   need,   and   explore   GitHub
               (<https://github.com/>) to see how they are being developed and used.

## OPTIONS
       The  Ruby  interpreter accepts the following command-line options (switches).  They are quite
       similar to those of [_perl_(1)](https://www.chedong.com/phpMan.php/man/perl/1/markdown).

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

       **--version      **Prints the version of the Ruby interpreter, and quits immediately without run‐
                      ning any script.

### -0
                      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 _
### -X _

### -E _
       **--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.**

       **--external-encoding**=_encoding_
       **--internal-encoding**=_encoding_
                      Specify the default external or internal character encoding

### -F _

### -I _
                      added to the load-path variable (**$:**).

### -K _
                      (**__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             
                      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 **$0 **does not always contain the full pathname, so you need the
                      **-S **switch to tell Ruby to search for the script if necessary (to handle embed‐
                      ded spaces and such).  A better construct than **$* **would be **${1+"$@"}**,  but  it
                      does not work if the script is being interpreted by [_csh_(1)](https://www.chedong.com/phpMan.php/man/csh/1/markdown).

### -T

### -U             
                      **UTF-8.**

### -W
                      sage 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.
                                    **-W**2 is the same as **-w**

### -a              -n  -p
                      executes
                            **$F = $_.split**
                      at beginning of each loop.

### -c             
                      there  are  no syntax errors, Ruby will print “Syntax OK” to the standard out‐
                      put.

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

### -e _
                      of the arguments for a script file name.

### -h
       **--help         **Prints a summary of the options.

### -i _
                      file name to make a backup copy.  For example:

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

### -l             
                      means to firstly set **$\ **to the value of **$/**, and secondly chops every line read
                      using **chomp!**.

### -n             
                      iterate over file name arguments somewhat like **sed -n **or **awk**.

                            while gets
                              ...
                            end

### -p             
                      end of the loop.  For example:

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

### -r _ -n  
                      **-p**.

### -s             
                      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             
                      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             
                      sets the **$VERBOSE **variable to true.

### -x
                      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.

### -y
       **--yydebug      **DO NOT USE.

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

       **--disable-_**FEATURE_
       **--enable-_**FEATURE_
                      Disables (or enables) the specified _FEATURE_.
                      **--disable-gems**
                      **--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  other‐
                                         wise.

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

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

       **--dump**=_target_  Dump some information.

                      Prints the specified target.  _target_ can be one of:

                            **version **Print version description (same as **--version).**

                            **usage   **Print a brief usage message (same as **-h).**

                            **help    **Show long help message (same as **--help).**

                            **syntax  **Check syntax (same as **-c --yydebug).**

                      Or one of the following, which are intended for debugging the interpreter:

                            **yydebug                 **Enable compiler debug mode (same as **--yydebug).**

                            **parsetree               **Print  a  textual representation of the Ruby AST
                                                    for the program.

                            **parsetree_with_comment  **Print a textual representation of the  Ruby  AST
                                                    for the program, but with each node annoted with
                                                    the associated Ruby source code.

                            **insns                   **Print  a  list of disassembled bytecode instruc‐
                                                    tions.

                            **insns_without_opt       **Print the list of disassembled bytecode instruc‐
                                                    tions before various optimizations have been ap‐
                                                    plied.

       **--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.

## ENVIRONMENT
       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.

                  e.g.:
                        **RUBYLIB="$HOME/lib/ruby:$HOME/lib/rubyext"**

       RUBYOPT    Additional Ruby options.

                  e.g.
                        **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)](https://www.chedong.com/phpMan.php/man/gem/1/markdown) as below.

             % gem help

## GC ENVIRONMENT
       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)](https://www.chedong.com/phpMan.php/man/malloc/3/markdown), [_calloc_(3)](https://www.chedong.com/phpMan.php/man/calloc/3/markdown), and [_realloc_(3)](https://www.chedong.com/phpMan.php/man/realloc/3/markdown)).  In this documentatation, the  "heap"  refers  to  the
       Ruby  object  heap  of fixed-sized slots, while "malloc" refers to auxiliary allocations com‐
       monly referred to as the "process heap".  Thus there are at least two possible ways to  trig‐
       ger 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 environ‐
       ment variables:
       RUBY_GC_HEAP_INIT_SLOTS                Initial allocation slots.  Introduced in Ruby 2.1, de‐
                                              fault: 10000.

       RUBY_GC_HEAP_FREE_SLOTS                Prepare at least this amount of slots after GC.  Allo‐
                                              cate 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.   Intro‐
                                              duced 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.  In‐
                                              troduced 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 un‐
                                              til 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_OLDMAL‐
                                              LOC_LIMIT_GROWTH_FACTOR.  Introduced in Ruby 2.1,  de‐
                                              fault: 128MB

       RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR  Increases  the  limit of old generation malloc alloca‐
                                              tion, 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
       Stack size environment variables are implementation-dependent and subject to change with dif‐
       ferent  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  ex‐
       tensions  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  excep‐
       tions  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:  524288
                                       (32-bit CPU) or 1048575 (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
                                       131072

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

## SEE ALSO
       <https://www.ruby-lang.org/>     The official web site.
       <https://www.ruby-toolbox.com/>  Comprehensive catalog of Ruby libraries.

## REPORTING BUGS
       **•   **Security vulnerabilities should be reported via an email to <_security@ruby-lang.org_>.   Re‐
           ported problems will be published after being fixed.

       **•   **Other  bugs  and  feature  requests  can  be  reported via the Ruby Issue Tracking System
           (<https://bugs.ruby-lang.org/>).  Do not report security vulnerabilities  via  this  system
           because it publishes the vulnerabilities immediately.

## AUTHORS
       Ruby is designed and implemented by Yukihiro Matsumoto <<matz@netlab.jp>>.

       See ⟨<https://bugs.ruby-lang.org/projects/ruby/wiki/Contributors>⟩ for contributors to Ruby.

UNIX                                       April 14, 2018                                    [_RUBY_(1)](https://www.chedong.com/phpMan.php/man/RUBY/1/markdown)