From: "Carlo E. Prelz" <fluido@...>
Date: 2013-01-17T18:23:22+09:00
Subject: Re: Escaped backslashes in input strings - newbie question

	Subject: Escaped backslashes in input strings - newbie question
	Date: Thu 17 Jan 13 06:05:06PM +0900

Quoting John Sampson (jrs.idx@ntlworld.com):

> If, at IRB, I write: x = "\b99m\BTc" (not \u which gives an 'invalid
> Unicode escape')
> and then: a.gsub(/\\./,"")
> the answer is "\b99mBTc".

That's because, in order to obtain the string you want to obtain, you
have to type

x = "\\b99m\\BTc" 

(note the double backslashes). If you then type

p x.length

you obtain 9. And if you type

p x.chars 

you obtain

=> ["\\", "b", "9", "9", "m", "\\", "B", "T", "c"]

The backslash is ONE character, but it is REPRESENTED as two
backslashes. 

The string you typed instead gives:

=> ["\b", "9", "9", "m", "B", "T", "c"]

\b is the way to represent a backspace. The other backslash disappears
because "\B" is not a special backslash sequence, and the non-escaped
character is returned.

One of the places where you can find a list of the valid backslash
sequence is this:

http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Literals

(search for 'Backslash Notation') If you ponder on all this jumble
with calm, you will see there is a sound logic behind it. If you think
this is messy, wait until you meet internationalization!

Carlo

-- 
  *         Se la Strada e la sua Virtu' non fossero state messe da parte,
* K * Carlo E. Prelz - fluido@fluido.as             che bisogno ci sarebbe
  *               di parlare tanto di amore e di rettitudine? (Chuang-Tzu)