1. def <=>(rhs)
Mode Strings
Ruby Language QuickRef # ...
r Read-only, starts at beginning of file (default mode).
end
def succ
r+ Read-write, starts at beginning of file.
# ...
General Syntax Rules end
end w Write-only, truncates existing file to zero length or creates a new file for writing.
Comments start with a pound/sharp (#) character and go to EOL. range = RangeThingy.new(lower_bound) .. RangeThingy.new(upper_bound)
w+ Read-write, truncates existing file to zero length or creates a new file for reading
Lines between ‘=begin’ and ‘=end’ are skipped by the interpreter.
Regexen and writing.
Ruby programs are sequence of expressions. /normal regex/[xim]
a Write-only, starts at end of file if file exists, otherwise creates a new file for
%r|alternate form|[xim]
Each expression is delimited by semicolons (;) or newlines unless obviously incomplete (e.g. writing.
Regex.new(pattern, options)
trailing ‘+’).
a+ Read-write, starts at end of file if file exists, otherwise creates a new file for
. any character except newline
Backslashes at the end of line does not terminate expression. reading and writing.
[set] any single character of set
b Binary file mode (may appear with any of the key letters listed above). Only
Reserved Words necessary for DOS/Windows.
[^set] any single character NOT of set
alias and BEGIN begin break case * 0 or more previous regular expression
Variables and Constants
class def defined do else elsif *? 0 or more previous regular expression (non greedy) $global_variable
END end ensure false for if @instance_variable
+ 1 or more previous regular expression [OtherClass::]CONSTANT
in module next nil not or local_variable
+? 1 or more previous regular expression (non greedy)
redo rescue retry return self super
Pseudo-variables
? 0 or 1 previous regular expression
then true undef unless until when
| alternation self the receiver of the current method
while yield
() grouping regular expressions nil the sole instance of NilClass (represents false)
^ beginning of a line or string true the sole instance of TrueClass (typical true value)
Types
Basic types are numbers, strings, ranges, regexen, symbols, arrays, and hashes. Also included are files because they are $ end of a line or string false the sole instance of FalseClass (represents false)
used so often.
#{m,n} at least m but most n previous regular expression __FILE__ the current source file name.
Numbers
#{m,n}? at least m but most n previous regular expression (non greedy)
123 1_234 123.45 1.2e-3 __LINE__ the current line number in the source file.
A beginning of a string
0xffff (hex) 0b01011 (binary) 0377 (octal)
Pre-defined Variables
b backspace (0x08, inside [] only)
?a ASCII character
$! The exception information message set by ‘raise’.
B non-word boundary
?C-a Control-a
$@ Array of backtrace of the last exception thrown.
b word boundary (outside [] only)
?M-a Meta-a
$& The string matched by the last successful pattern match in this scope.
d digit, same as[0-9]
?M-C-a Meta-Control-a
$` The string to the left of the last successful match.
D non-digit
Strings $' The string to the right of the last successful match.
S non-whitespace character
In all of the %() cases below, you may use any matching characters or any single character for delimiters. %[], %!!,
$+ The last bracket matched by the last successful match.
%@@, etc.
s whitespace character[ tnrf]
'no interpolation' $1 The Nth group of the last successful match. May be > 1.
W non-word character
quot;#{interpolation} and backslashesnquot;
$~ The information about the last match in the current scope.
w word character[0-9A-Za-z_]
%q(no interpolation)
$= The flag for case insensitive, nil by default.
z end of a string
%Q(interpolation and backslashes)
$/ The input record separator, newline by default.
Z end of a string, or before newline at the end
%(interpolation and backslashes)
$ The output record separator for the print and IO#write. Default is nil.
(?# ) comment
`echo command interpretation with interpolation and
$, The output field separator for the print and Array#join.
backslashes` (?: ) grouping without backreferences
$; The default separator for String#split.
%x(echo command interpretation with interpolation and (?= ) zero-width positive look-ahead assertion (?! )
backslashes) $. The current input line number of the last file that was read.
(?ix-ix) turns on/off i/x options, localized in group if any.
$< The virtual concatenation file of the files given on command line.
Backslashes (?ix-ix: ) turns on/off i/x options, localized in non-capturing group.
t (tab), n (newline), r (carriage return),
$> The default output for print, printf. $stdout by default.
f (form feed), b (backspace), a (bell),
e (escape), s (whitespace), nnn (octal),
Arrays $_ The last input line of string by gets or readline.
xnn (hexadecimal), cx (control x),
[1, 2, 3]
C-x (control x), M-x (meta x),
%w(foo bar baz) # no interpolation $0 Contains the name of the script being executed. May be assignable.
M-C-x (meta control x)
%W(foo #{bar} baz) # interpolation
$* Command line arguments given for the script sans args.
Here Docs Indexes may be negative, and they index backwards (-1 is the last element).
<<identifier # interpolation $$ The process number of the Ruby running this script.
Hashes
<<quot;identifierquot; # interpolation
{ 1 => 2, 2 => 4, 3 => 6 }
<<'identifier' # no interpolation $? The status of the last executed child process.
{ expr => expr, ... }
<<-identifier # interpolation, indented end
<<-quot;identifierquot; # interpolation, indented end $: Load path for scripts and binary modules by load or require.
<<-'identifier' # no interpolation, indented end
Files
$quot; The array contains the module names loaded by require.
Common methods include:
Symbols File.join(p1, p2, ... pN) => “p1/p2/.../pN© platform independent paths $DEBUG The status of the -d switch.
A symbol (:symbol) is an immutable name used for identifiers, variables, and operators.
Ranges File.new(path, mode_string=quot;rquot;) => file $FILENAME Current input file from $<. Same as $<.filename.
1..10
File.new(path, mode_num [, perm_num]) => file $LOAD_PATH The alias to the $:.
'a'..'z'
(1..10) === 5 -> true
File.open(filename, mode_string=quot;rquot;) {|file| block} -> nil $stderr The current standard error output.
(1..10) === 15 -> false
File.open(filename [, mode_num [, perm_num ]]) {|file| block} -> nil $stdin The current standard input.
# prints lines starting at 'start' and
# ending at 'end'
IO.foreach(path, sepstring=$/) {|line| block} $stdout The current standard output.
while gets
print if /start/../end/
IO.readlines(path) => array $VERBOSE The verbose flag, which is set by the -v switch.
end
$-0 The alias to $/.
class RangeThingy

2. # (comparisons may be regexen) methods and constants.
$-a True if option -a is set. Read-only variable. when comparison [, comparison]... [then] class A
body protected
$-d The alias to $DEBUG. when comparison [, comparison]... [then] def protected_method; ...; end
body end
$-F The alias to $;. ... class B < A
[else public
$-i In in-place-edit mode, this variable holds the extention, otherwise nil. body] def test_protected
end myA = A.new
$-I The alias to $:. myA.protected_method
while bool-expr [do] end
$-l True if option -l is set. Read-only variable. body end
end b = B.new.test_protected
$-p True if option -p is set. Read-only variable.
until bool-expr [do]
Accessors
$-v The alias to $VERBOSE. body
Module provides the following utility methods:
end
attr_reader <attribute>[, Creates a read-only accessor for each
Pre-defined Global Constants begin
<attribute>]... <attribute>.
body
TRUE The typical true value. end while bool-expr
attr_writer <attribute>[, Creates a write-only accessor for each
<attribute>]... <attribute>.
FALSE The false itself. begin
body
attr <attribute> [, Equivalent to quot;attr_reader <attribute>;
NIL The nil itself. end until bool-expr
<writable>] attr_writer <attribute> if
STDIN The standard input. The default value for $stdin. for name[, name]... in expr [do] <writable>quot;
body
STDOUT The standard output. The default value for $stdout. end attr_accessor <attribute>[, Equivalent to quot;attr <attribute>, truequot; for
<attribute>]... each argument.
STDERR The standard error output. The default value for $stderr. expr.each do | name[, name]... |
body
end
ENV The hash contains current environment variables.
Aliasing
alias <old> <new>
expr while bool-expr
ARGF The alias to the $<.
Creates a new reference to whatever old referred to. old can be any existing method, operator, global. It may not be a
expr until bool-expr
local, instance, constant, or class variable.
ARGV The alias to the $*.
Blocks, Closures, and Procs
break terminates loop immediately.
DATA The file object of the script, pointing just after __END__.
Blocks/Closures
redo immediately repeats w/o rerunning the condition.
RUBY_VERSION The ruby version string (VERSION was depricated). Blocks must follow a method invocation:
next starts the next iteration through the loop. invocation do ... end
RUBY_RELEASE_DATE The relase date string. invocation do || ... end
retry restarts the loop, rerunning the condition. invocation do |arg_list| ... end
RUBY_PLATFORM The platform identifier. invocation { ... }
invocation { || ... }
Invoking a Method invocation { |arg_list| ... }
Expressions Nearly everything available in a method invocation is optional, consequently the syntax is very difficult to follow. Here
Terms Blocks are full closures, remembering their variable context.
are some examples:
Terms are expressions that may be a basic type (listed above), a shell command, variable reference, constant reference, or method Blocks are invoked via yield and may be passed arguments.
method invocation.
obj.method
Operators and Precedence Block arguments may not have default parameters.
:: Class::method Brace form ({/}) has higher precedence and will bind to the last parameter if the invocation
is made without parentheses.
[] method(arg1, arg2)
do/end form has lower precedence and will bind to the invocation even without parentheses.
** method(arg1, key1 => val1, key2 => val2, aval1, aval2) { block }
- (unary) + (unary) ! ~ method(arg1, *[arg2, arg3]) becomes: method(arg1, arg2, arg3)
Proc Objects
* / % See class Proc for more information. Created via:
call := [receiver ('::' | '.')] name [params] [block] Kernel#proc (or Kernel#lambda)
params := ( [param]* [, hash] [*arr] [&proc] )
+ - Proc#new
block := { body } | do body end &block argument on a method
<< >>
Defining a Class Exceptions
&
Copyright © 2005 Ryan Davis with Austin Ziegler. PDF version by Austin Ziegler. Licensed under the
begin
Class names begin with capital characters.
| ^ expr
class Identifier [ < Superclass ]; ... ; end
[ rescue [ exception_class [ => var ], ... ]
> >= < <= expr ]
# Singleton classes, or idioclasses;
[ else
# add methods to a single instance
<=> == === != =~ !~ expr ]
# obj can be self
[ ensure
class << obj; ...; end
&& expr ]
end
Defining a Module
||
raise [ exception_class, ] [ message ]
Module names begin with capital characters.
.. ... module Identifier; ...; end
The default exception_class for rescue is StandardError, not Exception. Raise without an exception_class raises a
= (+=, -=, ...)
Defining a Method RuntimeError. All exception classes must inherit from Exception or one of its children (listed below).
def method_name(arg_list); ...; end
not StandardError LocalJumpError, SystemStackError, ZeroDivisionError, RangeError
def expr.method_name(arg_list); ...; end
(FloatDomainError), SecurityError, ThreadError, IOError (EOFError),
and or
ArgumentError, IndexError, RuntimeError, TypeError,
arg_list := ['('] [varname*] ['*' listname] ['&' blockname] [')'] SystemCallError (Errno::*), RegexpError
Control Expressions Arguments may have default values (varname = expr). SignalException
if bool-expr [then]
body Method definitions may not be nested. Interrupt
elsif bool-expr [then]
body method_name may be an operator: <=>, ==, ===, =~, <, <=, > >=, +, -, *, /, NoMemoryError
else
%, **, <<, >>, ~, +@, -@, [], []= (the last takes two arguments)
body
ScriptError LoadError, NameError, SyntaxError, NotImplementedError
end
Access Restriction SystemExit
unless bool-expr [then]
body public totally accessable.
else
Catch and Throw
body protected accessable only by instances of class and direct descendants. Even through
end catch :label do
hasA relationships. (see below) expr
expr if bool-expr throw :label
private accessable only by instances of class.
expr unless bool-expr end
case target-expr Restriction used without arguments set the default access control. Used with arguments, sets the access of the named