RUBY(1) 1 (ruby programmer's reference guide) RUBY(1)

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]
[--crash-report=template] [--] [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 ugliness, 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 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'.

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, without dependence on
Unicode.

Bignums
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-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) 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).

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

--version Prints the version of the Ruby interpreter, and quits
immediately 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.

--external-encoding=encoding
--internal-encoding=encoding
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 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 the 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.

--backtrace-limit=num
Limits the maximum length of backtraces to num lines
(default -1, meaning no limit).

-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.

-d
--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.

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

-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
chomp!.

-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
...
end

-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 '$_.tr! "a-z", "A-Z"'
MATZ

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

-y
--yydebug This option is not guaranteed to be compatible.

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.

--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
otherwise.

--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
instructions.

insns_without_opt Print the list of
disassembled bytecode
instructions before
various optimizations have
been applied.

--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.

--crash-report=template
Sets the template of path name to save crash report.
See RUBY_CRASH_REPORT environment variable for details.

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) 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), 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.
Applies to all slot sizes.
Introduced in Ruby 2.1, default:
10000.

RUBY_GC_HEAP_%d_INIT_SLOTS Initial allocation of slots in a
specific heap. The available
heaps can be found in the keys
of `GC.stat_heap`. Introduced
in Ruby 3.3.

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

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: 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

CRASH REPORT ENVIRONMENT

RUBY_CRASH_REPORT The template of path name to save crash report.
default: none

Naming crash report files

The template can contain % specifiers which are substituted by the
following values when a crash report file is created:

%% A single % character.
%e Basename of executable.
%E Pathname of executable, with slashes (/) replaced by exclamation
marks (!).
%f Basename of the program name, $0.
%F Pathname of the program name, $0, with slashes (/) replaced by
exclamation marks (!).
%p PID of dumped process.
%t Time of dump, expressed as seconds since the Epoch, 1970-01-01
00:00:00 +0000 (UTC).
%NNN A character code in octal.

A single % at the end of the template is dropped from the core
filename, as is the combination of a % followed by any character other
than those listed above. All other characters in the template become a
literal part of the core filename. The template may include '/'
characters, which are interpreted as delimiters for directory names.

Piping crash reports to a program

If the first character of this file is a pipe symbol (|), then the
remainder of the line is interpreted as the command-line for a program
(or script) that is to be executed.

The pipe template is split on spaces into an argument list before the
template parameters are expanded.

SEE ALSO

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

REPORTING BUGS

+o Security vulnerabilities should be reported via an email to
security@ruby-lang.org. Reported problems will be published after
being fixed.

+o 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://github.com/ruby/ruby/graphs/contributors> for contributors
to Ruby.

UNIX April 14, 2018 UNIX