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Ruby QuickRef

Contents:

Language

General Tips

These are tips I've given over and over and over and over...

See github.com /chneukirchen /styleguide /raw /master /RUBY-STYLE for more.

General Syntax Rules

Reserved words

alias   and     BEGIN   begin   break   case    class   def     defined?
do      else    elsif   END     end     ensure  false   for     if
in      module  next    nil     not     or      redo    rescue  retry
return  self    super   then    true    undef   unless  until   when
while   yield

Types

Basic types are numbers, strings, ranges, regexen, symbols, arrays, and hashes. Also included are files because they are used so often.

Numbers

123 1_234 123.45 1.2e-3 0xffff (hex) 0b01011 (binary) 0377 (octal)
?a       ASCII character
?\C-a    Control-a
?\M-a    Meta-a
?\M-\C-a Meta-Control-a

Strings

In all of the %() cases below, you may use any matching characters or any single character for delimiters. %[], %!!, %@@, etc.

'no interpolation'
"#{interpolation}, and backslashes\n"
%q(no interpolation)
%Q(interpolation and backslashes)
%(interpolation and backslashes)
`echo command interpretation with interpolation and backslashes`
%x(echo command interpretation with interpolation and backslashes)
Backslashes
\t (tab), \n (newline), \r (carriage return), \f (form feed), \b
(backspace), \a (bell), \e (escape), \s (whitespace), \nnn (octal),
\xnn (hexadecimal), \cx (control x), \C-x (control x), \M-x (meta x),
\M-\C-x (meta control x)
Here Docs
<<identifier   - interpolated, goes until identifier
<<"identifier" - same thing
<<'identifier' - no interpolation
<<-identifier  - you can indent the identifier by using "-" in front

Symbols

Internalized String. Guaranteed to be unique and quickly comparable. Ideal for hash keys. Symbols may not contain \0 or be empty.

:symbol                         => :symbol
:'#{"without"} interpolation'  => :"#{"without"} interpolation"
:"#{"with"} interpolation"     => :"with interpolation"
%s(#{"without"} interpolation) => :"#{"without"} interpolation"

Ranges

1..10
1...10
'a'..'z'
'a'...'z'
(1..10)  === 5   => true
(1..10)  === 10  => true
(1...10) === 10  => false
(1..10)  === 15  => false
while gets # prints lines starting at 'start' and ending at 'end'
  print if /start/../end/
end
class Comparable
  # ...
  def <=>(rhs)
    # ...
  end
  def succ
    # ...
  end
end
range = RangeThingy.new(lower_bound)..RangeThingy.new(upper_bound)

Regexen

Test out your regexen in irb or on: www.rubyxp.com

Usual recommended form:

str =~ /regex/

Lexical options:

/normal regex/iomx[neus]
%rXalternate formX (where X can be any character or pair () {} etc)

options:

/i         case insensitive
/o         only interpolate #{} blocks once
/m         multiline mode - '.' will match newline
/x         extended mode - whitespace is ignored
/[neus]    encoding: none, EUC, UTF-8, SJIS, respectively

regex characters:

.             any character except newline
[ ]           any single character of set
[^ ]          any single character NOT of set
*             0 or more previous regular expression
*?            0 or more previous regular expression (non-greedy)
+             1 or more previous regular expression
+?            1 or more previous regular expression (non-greedy)
?             0 or 1 previous regular expression
|             alternation
( )           grouping regular expressions
^             beginning of a line or string
$             end of a line or string
{m,n}         at least m but most n previous regular expression
{m,n}?        at least m but most n previous regular expression (non-greedy)
\1-9          nth previous captured group
\&            whole match
\`            pre-match
\'            post-match
\+            highest group matched
\A            beginning of a string
\b            backspace(0x08)(inside[]only)
\b            word boundary(outside[]only)
\B            non-word boundary
\d            digit, same as[0-9]
\D            non-digit
\S            non-whitespace character
\s            whitespace character[ \t\n\r\f]
\W            non-word character
\w            word character[0-9A-Za-z_]
\z            end of a string
\Z            end of a string, or before newline at the end
(?#)          comment
(?:)          grouping without backreferences
(?=)          zero-width positive look-ahead assertion
(?!)          zero-width negative look-ahead assertion
(?>)          nested anchored sub-regexp. stops backtracking.
(?imx-imx)    turns on/off imx options for rest of regexp.
(?imx-imx:re) turns on/off imx options, localized in group.

special character classes:

[:alnum:]   alpha-numeric characters
[:alpha:]   alphabetic characters
[:blank:]   whitespace - does not include tabs, carriage returns, etc
[:cntrl:]   control characters
[:digit:]   decimal digits
[:graph:]   graph characters
[:lower:]   lower case characters
[:print:]   printable characters
[:punct:]   punctuation characters
[:space:]   whitespace, including tabs, carriage returns, etc
[:upper:]   upper case characters
[:xdigit:]  hexadecimal digits

Arrays

[1, 2, 3]
%w(foo bar baz)
%W(foo bar baz #{var})

Indexes may be negative, and they index backwards (eg -1 is last element).

Hashes

{1=>2, 2=>4, 3=>6}
{ expr => expr...}

Files

Common methods include:

Mode Strings
r
Read-only, starts at beginning of file (default mode).
r+
Read-write, starts at beginning of file.
w
Write-only, truncates existing file to zero length or creates a new file for writing.
w+
Read-write, truncates existing file to zero length or creates a new file for reading and writing.
a
Write-only, starts at end of file if file exists, otherwise creates a new file for writing.
a+
Read-write, starts at end of file if file exists, otherwise creates a new file for reading and writing.
b
(DOS/Windows only) Binary file mode (may appear with any of the key letters listed above).

Variables

$global_variable
@@class_variable
@instance_variable
[OtherClass::]CONSTANT
local_variable

Pseudo variables

self     the receiver of the current method
nil      the sole instance of the Class NilClass(represents false)
true     the sole instance of the Class TrueClass(typical true value)
false    the sole instance of the Class FalseClass(represents false)
__FILE__ the current source file name.
__LINE__ the current line number in the source file.

Pre-defined variables

$!         The exception information message set by 'raise'.
$@         Array of backtrace of the last exception thrown.
$&         The string matched by the last successful match.
$`         The string to the left  of the last successful match.
$'         The string to the right of the last successful match.
$+         The highest group matched by the last successful match.
$1         The Nth group of the last successful match. May be > 1.
$~         The information about the last match in the current scope.
$=         The flag for case insensitive, nil by default.
$/         The input record separator, newline by default.
$\         The output record separator for the print and IO#write. Default is nil.
$,         The output field separator for the print and Array#join.
$;         The default separator for String#split.
$.         The current input line number of the last file that was read.
$<         The virtual concatenation file of the files given on command line (or from $stdin if no files were given).
$>         The default output for print, printf. $stdout by default.
$_         The last input line of string by gets or readline.
$0         Contains the name of the script being executed. May be assignable.
$*         Command line arguments given for the script sans args.
$$         The process number of the Ruby running this script.
$?         The status of the last executed child process.
$:         Load path for scripts and binary modules by load or require.
$"         The array contains the module names loaded by require.
$DEBUG     The status of the -d switch.
$FILENAME  Current input file from $<. Same as $<.filename.
$LOAD_PATH The alias to the $:.
$stderr    The current standard error output.
$stdin     The current standard input.
$stdout    The current standard output.
$VERBOSE   The verbose flag, which is set by the -v switch.
$-0        The alias to $/.
$-a        True if option -a is set. Read-only variable.
$-d        The alias to $DEBUG.
$-F        The alias to $;.
$-i        In in-place-edit mode, this variable holds the extension, otherwise nil.
$-I        The alias to $:.
$-l        True if option -l is set. Read-only variable.
$-p        True if option -p is set. Read-only variable.
$-v        The alias to $VERBOSE.
$-w        True if option -w is set.

Pre-defined global constants

TRUE              The typical true value.
FALSE             The false itself.
NIL               The nil itself.
STDIN             The standard input. The default value for $stdin.
STDOUT            The standard output. The default value for $stdout.
STDERR            The standard error output. The default value for $stderr.
ENV               The hash contains current environment variables.
ARGF              The alias to the $<.
ARGV              The alias to the $*.
DATA              The file object of the script, pointing just after __END__.
RUBY_VERSION      The ruby version string (VERSION was deprecated).
RUBY_RELEASE_DATE The release date string.
RUBY_PLATFORM     The platform identifier.

Expressions

Terms

Terms are expressions that may be a basic type (listed above), a shell command, variable reference, constant reference, or method invocation.

Operators and Precedence

(Top to bottom)
:: .
[]
**
-(unary) +(unary) ! ~
*  /  %
+  -
<<  >>
&
|  ^
>  >=  <  <=
<=> == === != =~ !~
&&
||
.. ...
=(+=, -=...)
not
and or

All of the above are just methods except these:

=, ::, ., .., ..., !, not, &&, and, ||, or, !=, !~

In addition, assignment operators(+= etc.) are not user-definable.

NOTE: 1.9 has a horrible extension to allow you to define != and !~. A special place in hell is reserved for you if you define those.

Control Expressions

if bool-expr [then]
  body
elsif bool-expr [then]
  body
else
  body
end
unless bool-expr [then]
  body
else
  body
end
expr if     bool-expr
expr unless bool-expr
bool-expr ? true-expr : false-expr
case target-expr
  when comparison [, comparison]... [then]
    body
  when comparison [, comparison]... [then]
    body
  ...
[else
  body]
end

(comparisons may be regexen)

loop do
  body
end
while bool-expr [do]
 body
end
until bool-expr [do]
 body
end
begin
 body
end while bool-expr
begin
 body
end until bool-expr
for name[, name]... in expr [do]
  body
end
expr.each do | name[, name]... |
  body
end
expr while bool-expr
expr until bool-expr

Invoking a Method

Nearly everything available in a method invocation is optional, consequently the syntax is very difficult to follow. Here are some examples:

invocation := [receiver ('::' | '.')] name [ parameters ] [ block ]
parameters := ( [param]* [, hashlist] [*array] [&aProc] )
block      := { blockbody } | do blockbody end

Defining a Class

Class names begin w/ capital character.

class Identifier [< superclass ]
  expr..
end
# singleton classes, add methods to a single instance
class << obj
  expr..
end

Defining a Module

module Identifier
  expr..
end

Defining a Method

def method_name(arg_list, *list_expr, &block_expr)
  expr..
end
# singleton method
def expr.identifier(arg_list, *list_expr, &block_expr)
  expr..
end

Access Restriction

class A
  protected
  def protected_method
    # nothing
  end
end
class B < A
  public
  def test_protected
    myA = A.new
    myA.protected_method
  end
end
b = B.new.test_protected

Accessors

Class Module provides the following utility methods:

attr_reader <attribute>[, <attribute>]...
Creates a read-only accessor for each <attribute>.
attr_writer <attribute>[, <attribute>]...
Creates a write-only accessor for each <attribute>.
attr <attribute> [, <writable>]
Equivalent to "attr_reader <attribute>; attr_writer <attribute> if <writable>"
attr_accessor <attribute>[, <attribute>]...
Equivalent to "attr <attribute>, TRUE" for each argument.

Aliasing

alias        :new  :old
alias_method :new, :old

Creates a new reference to whatever old referred to. old can be any existing method, operator, global. It may not be a local, instance, constant, or class variable.

Blocks, Closures, and Procs

Blocks/Closures

invocation do ... end
invocation { ... }

Proc Objects

Created via:

See class Proc for more information.

Exceptions, Catch, and Throw

Raising and Rescuing

raise ExceptionClass[, "message"]
begin
  expr..
[rescue [error_type [=> var],..]
  expr..]..
[else
  expr..]
[ensure
  expr..]
end

Catch and Throw

Standard Library

Ruby comes with an extensive library of classes and modules. Some are built-in, and some are part of the standard library. You can distinguish the two by the fact that the built-in classes are in fact, built-in. There are no dot-rb files for them.

Built-in Library

Class Hierarchy

Modules

Standard Library

The essentials:

Tools

ruby

Command Line Options

-0[octal]       specify record separator (\0, if no argument).
-a              autosplit mode with -n or -p (splits $_ into $F).
-c              check syntax only.
-Cdirectory     cd to directory, before executing your script.
--copyright     print the copyright and exit.
-d              set debugging flags (set $DEBUG to true).
-e 'command'    one line of script. Several -e's allowed.
-F regexp       split() pattern for autosplit (-a).
-h		  prints summary of the options.
-i[extension]   edit ARGV files in place (make backup if extension supplied).
-Idirectory     specify $LOAD_PATH directory (may be used more than once).
-Kkcode         specifies KANJI (Japanese) code-set.
-l              enable line ending processing.
-n              assume 'while gets(); ... end' loop around your script.
-p              assume loop like -n but print line also like sed.
-rlibrary       require the library, before executing your script.
-s              enable some switch parsing for switches after script name.
-S              look for the script using PATH environment variable.
-T[level]       turn on tainting checks.
-v              print version number, then turn on verbose mode.
--version       print the version and exit.
-w              turn warnings on for your script.
-x[directory]   strip off text before #! line and perhaps cd to directory.
-X directory    causes Ruby to switch to the directory.
-y              turns on compiler debug mode.

Environment Variables

DLN_LIBRARY_PATH Search path for dynamically loaded modules.
RUBYLIB          Additional search paths.
RUBYLIB_PREFIX   Add this prefix to each item in RUBYLIB. Windows only.
RUBYOPT          Additional command line options.
RUBYPATH         With -S, searches PATH, or this value for ruby programs.
RUBYSHELL        Shell to use when spawning.

irb

irb [options] [script [args]]

The essential options are:

-d              Sets $DEBUG to true. Same as "ruby -d ..."
-f              Prevents the loading of ~/.irb.rc.
-h              Get a full list of options.
-m              Math mode. Overrides --inspect. Loads "mathn.rb".
-r module       Loads a module. Same as "ruby -r module ..."
-v              Prints the version and exits.
--inf-ruby-mode Turns on emacs support and turns off readline.
--inspect       Turns on inspect mode. Default.
--noinspect     Turns off inspect mode.
--noprompt      Turns off the prompt.
--noreadline    Turns off readline support.
--prompt        Sets to one of 'default', 'xmp', 'simple', or 'inf-ruby'.
--readline      Turns on readline support. Default.
--tracer        Turns on trace mode.

Besides arbitrary ruby commands, the special commands are:

exit                  exits the current session, or the program
fork block            forks and runs the given block
cb args               changes to a secified binding
source file           loads a ruby file into the session
irb [obj]             starts a new session, with obj as self, if specified
conf[.key[= val]]     access the configuration of the session
jobs                  lists the known sessions
fg session            switches to the specifed session
kill session          kills a specified session

Session may be specified via session#, thread-id, obj, or self.

xmp

require "irb/xmp"
xmp "something to eval" # or:
x = XMP.new
x.puts "something to eval"

ruby-mode

TODO: I don't have a freakin clue how to use the inferior ruby thing... I always fire up a shell in emacs... DOH!

Debugger

To invoke the debugger:

ruby -r debug ...

To use the debugger:

b[reak] [file:|class:]<line|method
b[reak] [class.]<line|method
                           set breakpoint to some position
wat[ch] expression         set watchpoint to some expression
cat[ch] exception          set catchpoint to an exception
b[reak]                    list breakpoints
cat[ch]                    show catchpoint
del[ete][ nnn]             delete some or all breakpoints
disp[lay] expression       add expression into display expression list
undisp[lay][ nnn]          delete one particular or all display expressions
c[ont]                     run until program ends or hit breakpoint
s[tep][ nnn]               step (into methods) one line or till line nnn
n[ext][ nnn]               go over one line or till line nnn
w[here]                    display frames
f[rame]                    alias for where
l[ist][ (-|nn-mm)]         list program, - lists backwards
                           nn-mm lists given lines
up[ nn]                    move to higher frame
down[ nn]                  move to lower frame
fin[ish]                   return to outer frame
tr[ace] (on|off)           set trace mode of current thread
tr[ace] (on|off) all       set trace mode of all threads
q[uit]                     exit from debugger
v[ar] g[lobal]             show global variables
v[ar] l[ocal]              show local variables
v[ar] i[nstance] object    show instance variables of object
v[ar] c[onst] object       show constants of object
m[ethod] i[nstance] obj    show methods of object
m[ethod] class|module      show instance methods of class or module
th[read] l[ist]            list all threads
th[read] c[ur[rent]]       show current thread
th[read] [sw[itch]] nnn    switch thread context to nnn
th[read] stop nnn          stop thread nnn
th[read] resume nnn        resume thread nnn
p expression               evaluate expression and print its value
h[elp]                     print this help
everything else            evaluate
empty                      repeats the last command

rdoc

Structure

=     Level One Heading
==    Level Two Heading, and so on
*     bullet list
-     bullet list
1.    numbered list
[cat] labeled list
cat:: labeled list, tabular format
---   horizontal line (rule)

Formatting

_italic_      italic text
*bold*        bold text
+typewriter+  typewriter or mono-spaced text
\+escaped+    escaped, not special formatting

Hyperlinks

http://example.com/index.html        converts to external link, shows link
[home]http://example.com/index.html  converts to external link, shows "home"
link:/some/file/on/my/disk           converts to link to local file

Metadata

# :yields: ...      on method description, ... are yield parameters
# :nodoc:[all]      don't include this element in documentation, all for sub-elements too
# :doc:             force an element to be documented
# :notnew:          do not assume initialize arguments are for the new method
# --                in comment stop rdoc processing
# ++                in comment start rdoc processing again
# :include:filename include filename at this point
# :title:text       set the title for this document to text
# :main:name        set the class, module, or file to appear on the index page
=begin
the everything between a line beginning with `=begin' and
that with `=end' will be skipped by the ruby interpreter.
=end

Command Line Options

Run `rdoc --help` for full listing. Here are the more common flags:

--all, -a
include all methods (not just public) in the output
--diagram, -d
Generate diagrams showing modules and classes.
--exclude, -x pattern
Do not process files or directories matching pattern.
--force-update, -U
forces to scan all sources even if newer than the flag file.
--fmt, -f format name
Output using output formatters: chm, html, ri, xml (pluggable)
--inline-source, -S
Show method source code inline, rather than via a popup link
--main, -m name
'name' will be the initial page displayed
--op, -o dir
Set the output directory.
--ri, -r
generate ri output files to ~/.rdoc.
--style, -s stylesheet url
Specifies the URL of a separate stylesheet.
--template, -T template
Set the template used when generating output
--title, -t text
Set 'text' as the title for the output.

Mindshare, Idiom and Patterns

Object Design

Visitor Pattern

By defining the method #each and including Enumerable, you get to use all the methods in Enumerable:

class Mailbox
  include Enumerable
  # ...
  def each
    @mail.each do
       # ...
       yield
    end
  end
end

Class SimpleDelegator, DelegateClass

foo = Object.new
foo2 = SimpleDelegator.new(foo)
foo.hash == foo2.hash # => false
Foo = DelegateClass(Array)
class ExtArray<DelegateClass(Array)
  ...
end

Module Observer

monitor.add_observer(self)
...
def update
  ...
  notify_observers(data, ...)
end

Module Singleton

class Klass
  include Singleton
  # ...
end
a, b = Klass.instance, Klass.instance
a == b # => true
a.new  # raises NoMethodError

Other Third-party Libraries

Racc

Test::Unit

Original URL: www.zenspider.com/Languages/Ruby/QuickRef.html
$Author: ryand $
$Date: 2010/09/02 $
$Revision: #61 $

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