This document provides an overview of the default directory structure and pre-defined variables in Ruby on Rails. It lists the main directories like app, config, db, and lib. It also outlines key pre-defined variables like $!, $_, $stderr, and exceptions. Regular expressions syntax is defined at the bottom.

1. DEFAULT DIRECTORY STRUCTURE PRE-DEFINED VARIABLES Methods
$! Exception information Arrays
rails_root
assoc
app $& String of last match
at
apis $` String left of last match clear
controllers $' String right of last match collect!
$+ Last group of last match compact!
application.rb concat
helpers $N Nth group of last match delete
application_helper.rb $= Case insensitive flag delete_at
$/ Input record separator delete_if
models
Methods $ Output record separator
each
views each_index
Strings layouts $, Output field separator empty?
capitalize! $. Current line number of eql?
center components
chomp! last file read fill
config first
chop! $> Default output for print
concat environments flatten!
count development.rb $_ Last input line of string include?
crypt $0 Name of script index
delete! production.rb
indexes
downcase! test.rb $* Command line arguments
join
dump $stderr Standard error output
each database.yml last
each_byte $stdin Standard input length
environment.rb
empty? nitems
routes.rb $stdout Standard output
gsub! pack
hash db $-a True if -a is set. pop
hex $-d Status of -d switch push
include? doc
index $-l True if -l is set rassoc
lib reject!
intern $-p True if -p is set
length log replace
ljust, rjust development.log $-v Verbose Flag reverse!
next! reverse_each
oct production.log
rindex
replace server.log RESERVED WORDS shift
reverse!
rindex test.log slice!
=begin elsif rescue sort!
scan public
slice! =end end retry uniq!
split images unshift
BEGIN ensure return
squeeze! javascripts
strip! END false self Validation
sub! controls.js
alias for super condition_block?
sum dragdrop.js
swapcase! and if then create!
tr! effects.js evaluate_condition
begin in true
tr_s! prototype.js validate
unpack break module undef validate_on_create
upcase! stylesheets
case next unless validate_on_update
upto .htaccess validates_acceptance_of
class nil until
Regex 404.html validates_associated
def not when validates_confirmation_of
escape 500.html
last_match defined? or while validates_each
new dispatch.cgi
do redo yield validates_exclusion_of
quote dispatch.fcgi validates_format_of
casefold? else validates_inclusion_of
kcode dispatch.rb
validates_length_of
match favicon.ico
source REGULAR EXPRESSIONS SYNTAX validates_numericality_of
index.html validates_presence_of
Time script validates_size_of
asctime ^ Start of string validates_uniqueness_of
test
ctime $ End of string
day fixtures Enumerable Mixin
gmt? . Any single character
functional collect
gmtime (a|b) a or b
hour mocks each_with_index
isdst (...) Group section entries
development
localtime [abc] Item in range (a or b or c) find
mday test find_all
min [^abc] Not in range (not a or b or c)
unit grep
mon a? Zero or one of a
test_helper.rb include?
month
sec a* Zero or more of a max
vendor min
strftime a+ One or more of a
tv_sec reject
tv_usec a{3} Exactly 3 of a sort
usec METHODS NOTE a{3,} 3 or more of a
utc Available free from
utc? a{3,6} Between 3 and 6 of a
! - Denotes where a tailing ! may be AddedBytes.com
wday !(pattern) "Not" prefix. Apply rule when
yday ! - used. A colourless ! denotes that the
year URL does not match pattern. Ruby on Rails Logo
! - ! is compulsory.
zone used with permission.