From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2013-01-17T18:27:45+09:00
Subject: Re: Escaped backslashes in input strings - newbie question

On Thu, Jan 17, 2013 at 10:05 AM, John Sampson <jrs.idx@ntlworld.com> wrote:
> On 16/01/2013 21:53, Robert Klemme wrote:
>>
>> On Wed, Jan 16, 2013 at 6:55 PM, John Sampson <jrs.idx@ntlworld.com>
>> wrote:
>>>
>>> Input would be, for example, as (part of) a line in a text file,
>>> "\u99m\UTc". The desired output in this case would be "99mTc".
>>>
>>> The objective is to delete the "\u" and the "\U" and any other single
>>> letters where they are preceded by a backslash.
>>
>> OK, understood so far.  This is what you wrote right from the start.
>> But what's actually not working?
>>
>> robert
>>
> If, at IRB, I write: x = "\b99m\BTc" (not \u which gives an 'invalid Unicode
> escape')
> and then: a.gsub(/\\./,"")
> the answer is "\b99mBTc".

The problem is that what you wrote is not what you meant. In Ruby
code: "\b" is a single character:

1.9.2p290 :002 > "\b".length
 => 1

To have the same thing you will have when reading from a file, you
should escape the \ in string literals:

1.9.2p290 :003 > "\\b".length
 => 2

So,

1.9.2p290 :005 > "\\b1234\\c5678".gsub(/\\./, "")
 => "12345678"

> I am trying to get "99mTc", which I do get provided that I escape "\b" and
> "\B" with
> extra backslashes, but in file input these extra backslashes will be absent.
> I think on
> investigation that the extra backslashes will not be needed in that, but not
> necessarily
> any other, context.

Exactly, source code is different from a file that you read.

Jesus.