Quickref

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Thanks to Ryan Davis for contributing his Ruby Quickref. This page is locked, so if you have additional information you'd like to add, put it in the appropriate places under Ruby Language or the other detailed articles.

Contents

Language

General Syntax Rules

  • Comments start with a pound/sharp (#) character and go to EOL.
  • Ruby programs are sequence of expressions.
  • Each expression is delimited by semicolons(;) or newlines unless obviously incomplete (e.g. trailing '+').
  • Backslashes at the end of line does not terminate expression.

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

 /normal regex/iomx[neus]
 %r|alternate form|

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)
 \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
 (?ix-ix)   turns on/off i/x options, localized in group if any.
 (?ix-ix: ) turns on/off i/x options, localized in non-capturing 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:

  • File.join(p1, p2, ... pN) => "p1/p2/.../pN" platform independent paths
  • File.new(path, modestring="r") => file
  • File.new(path, modenum [, permnum]) => file
  • File.open(fileName, aModeString="r") {|file| block} -> nil
  • File.open(fileName [, aModeNum [, aPermNum ]]) {|file| block} -> nil
  • IO.foreach(path, sepstring=$/) {|line| block}
  • IO.readlines(path) => array
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 pattern match in this scope.
 $`         The string to the left  of the last successful match.
 $'         The string to the right of the last successful match.
 $+         The last bracket 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.
 $\>         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 .
 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.

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

 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
  • break terminates loop immediately.
  • redo immediately repeats w/o rerunning the condition.
  • next starts the next iteration through the loop.
  • retry restarts the loop, rerunning the condition.

Invoking a Method

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

  • method
  • obj.method
  • Class::method
  • method(key1 =\> val1, key2 =\> val2)
    • is one argument for def method(hash_arg) !
  • method(arg1, *[arg2, arg3]) becomes: method(arg1, arg2, arg3)
  • as ugly as you want it to be:
    • method(arg1, key1 =\> val1, key2 =\> val2, *splat_arg) #\{ block } 
 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
  • All items of the arg list, including parens, are optional.
  • Arguments may have default values (name=expr).
  • Method_name may be operators (see above).
  • The method definitions can not be nested.
  • Methods may override operators: .., |, ^, \&, \<=\>, ==, ===, =~, \>, \>=, \<, \<=, +, -, *, /, %, **, \<\<, \>\>, ~, +@, -@, [], []= (2 args)

Access Restriction

  • public - totally accessible.
  • protected - accessible only by instances of class and direct descendants. Even through hasA relationships. (see below)
  • private - accessible only by instances of class (must be called nekkid no "self." or anything else).
  • Restriction used w/o arguments set the default access control.
  • Used with arguments, sets the access of the named methods and constants. 
 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

  • blocks must follow a method invocation: 
 invocation do ... end
 invocation { ... }
  • Blocks remember their variable context, and are full closures.
  • Blocks are invoked via yield and may be passed arguments.
  • Brace form has higher precedence and will bind to the last parameter if invocation made w/o parens.
  • do/end form has lower precedence and will bind to the invocation even without parens.

Proc Objects

Created via:

  • Kernel#proc
  • Proc#new
  • By invoking a method w/ a block argument.

See class Proc for more information.

Exceptions, Catch, and Throw

  • Exception
    • NoMemoryError
    • ScriptError
      • LoadError
      • NotImplementedError
      • SyntaxError
    • SignalException
      • Interrupt
    • StandardError (default for rescue)
      • ArgumentError
      • IOError
        • EOFError
      • IndexError
      • LocalJumpError
      • NameError
        • NoMethodError
      • RangeError
        • FloatDomainError
      • RegexpError
      • RuntimeError (default for raise)
      • SecurityError
      • SystemCallError
        • Errno::*
      • SystemStackError
      • ThreadError
      • TypeError
      • ZeroDivisionError
    • SystemExit
    • fatal

Raising and Rescuing

 raise ExceptionClass[, "message"]

 begin
   expr..
 [rescue [error_type [=> var],..]
   expr..]..
 [else
   expr..]
 [ensure
   expr..]
 end

Catch and Throw

  • catch (:label) do ... end
  • throw :label jumps back to matching catch and terminates the block.
    • can be external to catch, but has to be reached via calling scope.
    • Hardly ever needed.

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

  • Object
    • Hash
    • Symbol
    • IO
      • File
    • Continuation
    • File::Stat
    • Data
    • NilClass
    • Exception (see tree above)
    • Array
    • Proc
    • String
    • Numeric
      • Float
      • Integer
        • Bignum
        • Fixnum
    • Regexp
    • Thread
    • Module
      • Class
    • ThreadGroup
    • Method
      • UnboundMethod
    • Struct
      • Struct::Tms
    • TrueClass
    • Time
    • Dir
    • Binding
    • Range
    • MatchData
    • FalseClass

Modules

  • Comparable
  • Enumerable
  • Errno
  • FileTest
  • GC
  • Kernel
  • Marshal
  • Math
  • ObjectSpace
  • Precision
  • Process

Standard Library

The essentials:

  • benchmark.rb a simple benchmarking utility
  • cgi-lib.rb decode CGI data - simpler than cgi.rb
  • cgi.rb CGI interaction
  • date.rb date object (compatible)
  • debug.rb ruby debugger
  • delegate.rb delegate messages to other object
  • English.rb access global variables by english names
  • fileutils.rb file utility methods for copying, moving, removing, etc.
  • find.rb traverse directory tree
  • jcode.rb UTF-8 and Japanese String helpers (replaces String methods)
  • net/*.rb Networking classes of all kinds
  • observer.rb observer design pattern library (provides Observable)
  • open-uri.rb good wrapper for net/http, net/https and net/ftp
  • open3.rb open subprocess connection stdin/stdout/stderr
  • ostruct.rb python style object (freeform assignment to instance vars)
  • parsearg.rb argument parser using getopts
  • pp prettier debugging output, 'p' on steroids.
  • profile.rb ruby profiler - find that slow code!
  • pstore.rb persistent object strage using marshal
  • rexml/*.rb XML toolkit
  • singleton.rb singleton design pattern library
  • stringio lets you use an IO attached to a string.
  • tempfile.rb temporary file that automatically removed
  • test/unit unit testing framework
  • time.rb extension to Time class with a lot of converters
  • tracer.rb execution tracer
  • webrick Fairly spiffy web server
  • yaml alternative readable serialization format

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"

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

 =begin
 the everything between a line beginning with `=begin' and
 that with `=end' will be skipped by the interpreter.
 =end

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

  • assert(boolean, message=nil)
  • assert_block(message="assert_block failed.") do ... end
  • assert_equal(expected, actual, message=nil)
  • assert_in_delta(expected_float, actual_float, delta, message="")
  • assert_instance_of(klass, object, message="")
  • assert_kind_of(klass, object, message="")
  • assert_match(pattern, string, message="")
  • assert_nil(object, message="")
  • assert_no_match(regexp, string, message="")
  • assert_not_equal(expected, actual, message="")
  • assert_not_nil(object, message="")
  • assert_not_same(expected, actual, message="")
  • assert_nothing_raised(*args)
  • assert_nothing_thrown(message="") do ... end
  • assert_operator(object1, operator, object2, message="")
  • assert_raises(expected_exception_klass, message="") do ... end
  • assert_respond_to(object, method, message="")
  • assert_same(expected, actual, message="")
  • assert_send(send_array, message="")
  • assert_throws(expected_symbol, message="") do ... end
  • flunk(message="Flunked")
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