ruby/man/ruby.1

.\"Ruby is copyrighted by Yukihiro Matsumoto <matz@netlab.jp>.
.Dd April 14, 2018
.Dt RUBY \&1 "Ruby Programmer's Reference Guide"
.Os UNIX
.Sh NAME
.Nm ruby
.Nd Interpreted object-oriented scripting language
.Sh SYNOPSIS
.Nm
.Op Fl -copyright
.Op Fl -version
.Op Fl SUacdlnpswvy
.Op Fl 0 Ns Op Ar octal
.Op Fl C Ar directory
.Op Fl E Ar external Ns Op : Ns Ar internal
.Op Fl F Ns Op Ar pattern
.Op Fl I Ar directory
.Op Fl K Ns Op Ar c
.Op Fl T Ns Op Ar level
.Op Fl W Ns Op Ar level
.Op Fl e Ar command
.Op Fl i Ns Op Ar extension
.Op Fl r Ar library
.Op Fl x Ns Op Ar directory
.Op Fl - Ns Bro Cm enable Ns | Ns Cm disable Brc Ns - Ns Ar FEATURE
.Op Fl -dump Ns = Ns Ar target
.Op Fl -verbose
.Op Fl -
.Op Ar program_file
.Op Ar argument ...
.Sh 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.
.Pp
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.
.Sh FEATURES
Ruby's features are as follows:
.Bl -tag -width 6n
.It Sy "Interpretive"
Ruby is an interpreted language, so you don't have to recompile
programs written in Ruby to execute them.
.Pp
.It Sy "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.
.Pp
.It Sy "No declaration needed"
You can use variables in your Ruby programs without any declarations.
Variable names denote their scope - global, class, instance, or local.
.Pp
.It Sy "Simple syntax"
Ruby has a simple syntax influenced slightly from Eiffel.
.Pp
.It Sy "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.
.Pp
.It Sy "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.
.Pp
.It Sy "Class, inheritance, and methods"
Being an object-oriented language, Ruby naturally has basic
features like classes, inheritance, and methods.
.Pp
.It Sy "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.
.Pp
.It Sy "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
.Sq Mix-in .
.Pp
.It Sy "Iterators"
Ruby has iterators for loop abstraction.
.Pp
.It Sy "Closures"
In Ruby, you can objectify the procedure.
.Pp
.It Sy "Text processing and regular expressions"
Ruby has a bunch of text processing features like in Perl.
.Pp
.It Sy "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.
.Pp
.It Sy "Bignums"
With built-in bignums, you can for example calculate factorial(400).
.Pp
.It Sy "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.
.Pp
.It Sy "Exception handling"
As in Java(tm).
.Pp
.It Sy "Direct access to the OS"
Ruby can use most
.Ux
system calls, often used in system programming.
.Pp
.It Sy "Dynamic loading"
On most
.Ux
systems, you can load object files into the Ruby interpreter
on-the-fly.
.It Sy "Rich libraries"
In addition to the
.Dq builtin libraries
and
.Dq standard libraries
that are bundled with Ruby, a vast amount of third-party libraries
.Pq Dq gems
are available via the package management system called
.Sq RubyGems ,
namely the
.Xr gem 1
command.  Visit RubyGems.org
.Pq Lk https://rubygems.org/
to find the gems you need, and explore GitHub
.Pq Lk https://github.com/
to see how they are being developed and used.
.El
.Pp
.Sh OPTIONS
The Ruby interpreter accepts the following command-line options (switches).
They are quite similar to those of
.Xr perl 1 .
.Bl -tag -width "1234567890123" -compact
.Pp
.It Fl -copyright
Prints the copyright notice, and quits immediately without running any
script.
.Pp
.It Fl -version
Prints the version of the Ruby interpreter, and quits immediately without
running any script.
.Pp
.It Fl 0 Ns Op Ar octal
(The digit
.Dq zero . )
Specifies the input record separator
.Pf ( Li "$/" )
as an octal number. If no digit is given, the null character is taken
as the separator.  Other switches may follow the digits.
.Fl 00
turns Ruby into paragraph mode.
.Fl 0777
makes Ruby read whole file at once as a single string since there is
no legal character with that value.
.Pp
.It Fl C Ar directory
.It Fl X Ar directory
Causes Ruby to switch to the directory.
.Pp
.It Fl E Ar external Ns Op : Ns Ar internal
.It Fl -encoding Ar external Ns Op : Ns Ar internal
Specifies the default value(s) for external encodings and internal encoding. Values should be separated with colon (:).
.Pp
You can omit the one for internal encodings, then the value
.Pf ( Li "Encoding.default_internal" ) will be nil.
.Pp
.It Fl -external-encoding Ns = Ns Ar encoding
.It Fl -internal-encoding Ns = Ns Ar encoding
Specify the default external or internal character encoding
.Pp
.It Fl F Ar pattern
Specifies input field separator
.Pf ( Li "$;" ) .
.Pp
.It Fl I Ar directory
Used to tell Ruby where to load the library scripts.  Directory path
will be added to the load-path variable
.Pf ( Li "$:" ) .
.Pp
.It Fl K Ar kcode
Specifies KANJI (Japanese) encoding. The default value for script encodings
.Pf ( Li "__ENCODING__" ) and external encodings ( Li "Encoding.default_external" ) will be the specified one.
.Ar kcode
can be one of
.Bl -hang -offset indent
.It Sy e
EUC-JP
.Pp
.It Sy s
Windows-31J (CP932)
.Pp
.It Sy u
UTF-8
.Pp
.It Sy n
ASCII-8BIT (BINARY)
.El
.Pp
.It Fl S
Makes Ruby use the
.Ev PATH
environment variable to search for script, unless its name begins
with a slash.  This is used to emulate
.Li #!
on machines that don't support it, in the following manner:
.Bd -literal -offset indent
#! /usr/local/bin/ruby
# This line makes the next one a comment in Ruby \e
  exec /usr/local/bin/ruby -S $0 $*
.Ed
.Pp
On some systems
.Li "$0"
does not always contain the full pathname, so you need the
.Fl S
switch to tell Ruby to search for the script if necessary (to handle embedded
spaces and such).  A better construct than
.Li "$*"
would be
.Li ${1+"$@"} ,
but it does not work if the script is being interpreted by
.Xr csh 1 .
.Pp
.It Fl T Ns Op Ar level=1
Turns on taint checks at the specified level (default 1).
.Pp
.It Fl U
Sets the default value for internal encodings
.Pf ( Li "Encoding.default_internal" ) to UTF-8.
.Pp
.It Fl W Ns Op Ar level=2
Turns on verbose mode at the specified level without printing the version
message at the beginning. The level can be;
.Bl -hang -offset indent
.It Sy 0
Verbose mode is "silence". It sets the
.Li "$VERBOSE"
to nil.
.Pp
.It Sy 1
Verbose mode is "medium". It sets the
.Li "$VERBOSE"
to false.
.Pp
.It Sy 2 (default)
Verbose mode is "verbose". It sets the
.Li "$VERBOSE"
to true.
.Fl W Ns
2 is the same as
.Fl w
.
.El
.Pp
.It Fl a
Turns on auto-split mode when used with
.Fl n
or
.Fl p .
In auto-split mode, Ruby executes
.Dl $F = $_.split
at beginning of each loop.
.Pp
.It Fl -backtrace-limit Ns = Ns Ar num
Limits the maximum length of backtraces to
.Ar num
lines (default -1, meaning no limit).
.Pp
.It Fl c
Causes Ruby to check the syntax of the script and exit without
executing. If there are no syntax errors, Ruby will print
.Dq Syntax OK
to the standard output.
.Pp
.It Fl d
.It Fl -debug
Turns on debug mode.
.Li "$DEBUG"
will be set to true.
.Pp
.It Fl e Ar command
Specifies script from command-line while telling Ruby not to search
the rest of the arguments for a script file name.
.Pp
.It Fl h
.It Fl -help
Prints a summary of the options.
.Pp
.It Fl i Ar extension
Specifies in-place-edit mode.  The extension, if specified, is added
to old file name to make a backup copy.  For example:
.Bd -literal -offset indent
% echo matz > /tmp/junk
% cat /tmp/junk
matz
% ruby -p -i.bak -e '$_.upcase!' /tmp/junk
% cat /tmp/junk
MATZ
% cat /tmp/junk.bak
matz
.Ed
.Pp
.It Fl l
(The lowercase letter
.Dq ell . )
Enables automatic line-ending processing, which means to firstly set
.Li "$\e"
to the value of
.Li "$/" ,
and secondly chops every line read using
.Li chomp! .
.Pp
.It Fl n
Causes Ruby to assume the following loop around your script, which
makes it iterate over file name arguments somewhat like
.Nm sed
.Fl n
or
.Nm awk .
.Bd -literal -offset indent
while gets
  ...
end
.Ed
.Pp
.It Fl p
Acts mostly same as -n switch, but print the value of variable
.Li "$_"
at the each end of the loop.  For example:
.Bd -literal -offset indent
% echo matz | ruby -p -e '$_.tr! "a-z", "A-Z"'
MATZ
.Ed
.Pp
.It Fl r Ar library
Causes Ruby to load the library using require.  It is useful when using
.Fl n
or
.Fl p .
.Pp
.It Fl s
Enables some switch parsing for switches after script name but before
any file name arguments (or before a
.Fl - ) .
Any switches found there are removed from
.Li ARGV
and set the corresponding variable in the script.  For example:
.Bd -literal -offset indent
#! /usr/local/bin/ruby -s
# prints "true" if invoked with `-xyz' switch.
print "true\en" if $xyz
.Ed
.Pp
.It Fl v
Enables verbose mode.  Ruby will print its version at the beginning
and set the variable
.Li "$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.
.Pp
.It Fl w
Enables verbose mode without printing version message at the
beginning.  It sets the
.Li "$VERBOSE"
variable to true.
.Pp
.It Fl x Ns Op Ar directory
Tells Ruby that the script is embedded in a message.  Leading garbage
will be discarded until the first line that starts with
.Dq #!
and contains the string,
.Dq ruby .
Any meaningful switches on that line will be applied.  The end of the script
must be specified with either
.Li EOF ,
.Li "^D" ( Li "control-D" ) ,
.Li "^Z" ( Li "control-Z" ) ,
or the reserved word
.Li __END__ .
If the directory name is specified, Ruby will switch to that directory
before executing script.
.Pp
.It Fl y
.It Fl -yydebug
This option is not guaranteed to be compatible.
.Pp
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.
.Pp
.It Fl -disable- Ns Ar FEATURE
.It Fl -enable- Ns Ar FEATURE
Disables (or enables) the specified
.Ar FEATURE .
.Bl -tag -width "--disable-rubyopt" -compact
.It Fl -disable-gems
.It Fl -enable-gems
Disables (or enables) RubyGems libraries.  By default, Ruby will load the latest
version of each installed gem. The
.Li Gem
constant is true if RubyGems is enabled, false if otherwise.
.Pp
.It Fl -disable-rubyopt
.It Fl -enable-rubyopt
Ignores (or considers) the
.Ev RUBYOPT
environment variable. By default, Ruby considers the variable.
.Pp
.It Fl -disable-all
.It Fl -enable-all
Disables (or enables) all features.
.Pp
.El
.Pp
.It Fl -dump Ns = Ns Ar target
Dump some information.
.Pp
Prints the specified target.
.Ar target
can be one of:
.Bl -hang -offset indent
.It Sy version
Print version description (same as
.Fl -version).
.It Sy usage
Print a brief usage message (same as
.Fl h).
.It Sy help
Show long help message (same as
.Fl -help).
.It Sy syntax
Check syntax (same as
.Fl c
.Fl -yydebug).
.Pp
.El
.Pp
Or one of the following, which are intended for debugging the interpreter:
.Bl -hang -offset indent -tag -width "parsetree_with_comment"
.It Sy yydebug
Enable compiler debug mode (same as
.Fl -yydebug).
.It Sy parsetree
Print a textual representation of the Ruby AST for the program.
.It Sy 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.
.It Sy insns
Print a list of disassembled bytecode instructions.
.It Sy insns_without_opt
Print the list of disassembled bytecode instructions before various optimizations have been applied.
.El
.Pp
.It Fl -verbose
Enables verbose mode without printing version message at the
beginning.  It sets the
.Li "$VERBOSE"
variable to true.
If this switch is given, and no script arguments (script file or
.Fl e
options) are present, Ruby quits immediately.
.El
.Pp
.Sh ENVIRONMENT
.Bl -tag -width "RUBYSHELL" -compact
.It Ev RUBYLIB
A colon-separated list of directories that are added to Ruby's
library load path
.Pf ( Li "$:" ) . Directories from this environment variable are searched
before the standard load path is searched.
.Pp
e.g.:
.Dl RUBYLIB="$HOME/lib/ruby:$HOME/lib/rubyext"
.Pp
.It Ev RUBYOPT
Additional Ruby options.
.Pp
e.g.
.Dl RUBYOPT="-w -Ke"
.Pp
Note that RUBYOPT can contain only
.Fl d , Fl E , Fl I , Fl K , Fl r , Fl T , Fl U , Fl v , Fl w , Fl W, Fl -debug ,
.Fl -disable- Ns Ar FEATURE
and
.Fl -enable- Ns Ar FEATURE .
.Pp
.It Ev RUBYPATH
A colon-separated list of directories that Ruby searches for
Ruby programs when the
.Fl S
flag is specified.  This variable precedes the
.Ev PATH
environment variable.
.Pp
.It Ev 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
.Ev COMSPEC .
.Pp
.It Ev PATH
Ruby refers to the
.Ev PATH
environment variable on calling Kernel#system.
.El
.Pp
And Ruby depends on some RubyGems related environment variables unless RubyGems is disabled.
See the help of
.Xr gem 1
as below.
.Bd -literal -offset indent
% gem help
.Ed
.Pp
.Sh 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 (
.Xr malloc 3 ,
.Xr calloc 3 ,
and
.Xr 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:
.Bl -hang -offset indent
.It Sy 1
Reaching the object limit.
.It Sy 2
Reaching the malloc limit.
.Pp
.El
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:
.Bl -hang -offset indent
.It Sy 3
Reaching the old object limit.
.It Sy 4
Reaching the old malloc limit.
.El
.Pp
There are currently 4 possible areas where the GC may be tuned by
the following 11 environment variables:
.Bl -hang -compact -width "RUBY_GC_OLDMALLOC_LIMIT_GROWTH_FACTOR"
.It Ev RUBY_GC_HEAP_INIT_SLOTS
Initial allocation slots. Applies to all slot sizes.  Introduced in Ruby 2.1, default: 10000.
.Pp
.It Ev RUBY_GC_HEAP_INIT_SIZE_%d_SLOTS
Initial allocation of slots in a specific size pool.
The available size pools can be found in `GC.stat_heap`.
Introduced in Ruby 3.3.
.Pp
.It Ev 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
.Pp
.It Ev 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)
.Pp
.It Ev 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)
.Pp
.It Ev 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
.Pp
.It Ev 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
.Pp
.It Ev 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.
.Pp
.It Ev 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)
.Pp
.It Ev 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
.Pp
.It Ev 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
.Pp
.It Ev 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)
.Pp
.El
.Sh 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.
.Pp
.Bl -hang -compact -width "RUBY_THREAD_MACHINE_STACK_SIZE"
.It Ev RUBY_THREAD_VM_STACK_SIZE
VM stack size used at thread creation.
default: 524288 (32-bit CPU) or 1048575 (64-bit)
.Pp
.It Ev RUBY_THREAD_MACHINE_STACK_SIZE
Machine stack size used at thread creation.
default: 524288 or 1048575
.Pp
.It Ev RUBY_FIBER_VM_STACK_SIZE
VM stack size used at fiber creation.
default: 65536 or 131072
.Pp
.It Ev RUBY_FIBER_MACHINE_STACK_SIZE
Machine stack size used at fiber creation.
default: 262144 or 524288
.Pp
.El
.Sh SEE ALSO
.Bl -hang -compact -width "https://www.ruby-toolbox.com/"
.It Lk https://www.ruby-lang.org/
The official web site.
.It Lk https://www.ruby-toolbox.com/
Comprehensive catalog of Ruby libraries.
.El
.Pp
.Sh REPORTING BUGS
.Bl -bullet
.It
Security vulnerabilities should be reported via an email to
.Mt security@ruby-lang.org .
Reported problems will be published after being fixed.
.Pp
.It
Other bugs and feature requests can be reported via the
Ruby Issue Tracking System
.Pq Lk https://bugs.ruby-lang.org/ .
Do not report security vulnerabilities
via this system because it publishes the vulnerabilities immediately.
.El
.Sh AUTHORS
Ruby is designed and implemented by
.An Yukihiro Matsumoto Aq matz@netlab.jp .
.Pp
See
.Aq Lk https://github.com/ruby/ruby/graphs/contributors
for contributors to Ruby.