Ubuntu Manpage: ruby — Interpreted object-oriented scripting language

Provided by: ruby1.9.1_1.9.3.484-2ubuntu1.14_amd64

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 (as 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
Libraries called "builtin libraries" and "standard libraries" are bundled with Ruby. And you can
obtain more libraries via the package management system called `RubyGems'.

Moreover there are thousands of Ruby projects in Rubyforge (http://www.rubyforge.org) and RAA
(http://raa.ruby-lang.org).

OPTIONS

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.

-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 if 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 $*

-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 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.

-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 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
...
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

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 or such. A
better construct than $* would be ${1+"$@"}, but it does not work if the script is being
interpreted by csh(1).

-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 that starts with “#!” and contains the string, “ruby”. Any meaningful
switches on that line will applied. The end of 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 messages during
compiling scripts. You don't have to specify this switch, unless 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 DO NOT USE.

Prints the specified target. target can be one of;

insns disassembled instructions

You don't have to specify this switch, unless 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 other switches are present, Ruby
quits after printing its version.

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.

     RUBYLIB_PREFIX  This variable is obsolete.

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

           % gem help

REPORTING BUGS

     Security vulnerabilities should be reported via an email to ⟨security@ruby-lang.org⟩.  Reported problems
     will be published after they've been fixed.

     And you can report other bugs and feature requests via the Ruby Issue Tracking System (http://redmine.ruby-
     lang.org).  Do not report security vulnerabilities via the system because it publishes the vulnerabilities
     immediately.

AUTHORS

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

     See <http://redmine.ruby-lang.org/wiki/ruby/Contributors> for contributors to Ruby.