Rails City

“Regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters.

The following examples illustrate a few specifications that could be expressed in a regular expression:

* the sequence of characters “car” in any context, such as “car”, “cartoon”, or “bicarbonate”
* the word “car” when it appears as an isolated word
* the word “car” when preceded by the word “blue” or “red”
* a dollar sign immediately followed by one or more digits, and then optionally a period and exactly two more digits

Regular expressions can be much more complex than these examples.” (from Wikipedia)

Now, open a terminal, introduce “irb” or go to tryruby and continue playing:

1. "My child loves cartoons and dogs"=~/car/
=> 14

# \s: whitespace
"My child loves cartoons and dogs"=~/[\s]car[\s]/
=> nil

"My child loves cars and dogs"=~/[\s]cars[\s]/
=> 14

"My child loves cars! and dogs"=~/[\s]cars[\s]/
=> nil

# \w: any word character
# [^\w]: any character except word characters
"My child loves cars!"=~/[^\w]cars[^\w]/
=> 14

"My child loves cars"=~/[^\w]cars[^\w]/
=> nil

#$ end of the string
"My child loves cars"=~/[^\w]cars$/
=> 14

#([^\w]|$) any non word character or end of the string
"My child loves cars"=~/[^\w]cars([^\w]|$)/
=> 14

"My child loves blue cars"=~/blue cars/
=> 15

"My child loves red cars"=~/(blue|red) cars/

=> 15
$1
=> red

"My child loves blue cars"=~/(blue|red) cars/
=> 15
$1
=> blue

More info here: