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RUBY(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] [--] [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 ug-
liness, 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
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 sin-
gleton methods, if you want to.
Mix-in by modules
Ruby intentionally does not have the multiple inheritance as it is a source of con-
fusion. Instead, Ruby has the ability to share implementations across the inheri-
tance 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).
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 em-
bedded 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 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 out-
put.
-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 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
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 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 in-
terpreter.
parsetree
parsetree_with_comment AST nodes tree
Only specify this switch if you are going to debug the Ruby in-
terpreter.
insns disassembled instructions
Only specify this switch if you are going to debug the Ruby in-
terpreter.
--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) 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 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,
default: 10000.
RUBY_GC_HEAP_FREE_SLOTS Prepare at least this amount of slots after GC. Al-
locate 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 fac-
tor. 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.
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. Intro-
duced 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 mal-
loc growth until RUBY_GC_OLDMALLOC_LIMIT_MAX is
reached. Introduced in Ruby 2.1, default: 1.2, mini-
mum: 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 vir-
tual 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 applica-
tions 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
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
o Security vulnerabilities should be reported via an email to security AT ruby-lang.org. Re-
ported 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 AT netlab.jp>.
See <https://bugs.ruby-lang.org/projects/ruby/wiki/Contributors> for contributors to Ruby.
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