From: Alexandru Popescu <the.mindstorm.mailinglist@...>
Date: 2006-01-19T00:56:03+09:00
Subject: Re: how to double single quote (beginner blockage)

#: Gavin Kistner changed the world a bit at a time by saying (astral date: 1/18/2006 5:28 PM) :#
> On Jan 18, 2006, at 7:47 AM, Alexandru Popescu wrote:
>> if I have a string that contains single quote (f.e. "al'alamein") i  
>> would like to escape it with another single quote (=> "al''alamein").
>>
>> there are cases when these strings are already escaped according to  
>> the above rule, so those should remain untouched
> 
> Let's build this step by step.
> 
> The simple case is pretty simple, using Regular Expressions. You want  
> to find a single quote that has characters other than a single quote  
> on either side, and replace it with two single quotes:
> 
> irb(main):001:0> input = "al'alamein"
> => "al'alamein"
> irb(main):002:0> input.gsub( /([^'])'([^'])/, "\\1''\\2" )
> => "al''alamein"
> 
> The above breaks if the single quote occurs at the beginning or end  
> of the input:
> irb(main):003:0> input2 = "'Hey, it's al'alamein'"
> => "'Hey, it's al'alamein'"
> irb(main):004:0> input2.gsub( /([^'])'([^'])/, "\\1''\\2" )
> => "'Hey, it''s al''alamein'"
> 
> ...so let's say that there has to be a non-single quote at either  
> end, OR the start/end of the string:
> irb(main):005:0> input2.gsub( /(\A|[^'])'([^']|\Z)/, "\\1''\\2" )
> => "''Hey, it''s al''alamein''"
> 
> Finally, the above handles 1 or 2 single quotes in a row correctly,  
> but not 3 or more. Probably you want to ensure that single quotes  
> always come in even-numbered runs.
> 
> Instead of looking for a single quote in the middle of that regular  
> expression, we'll look for a single quote followed by an even number  
> of single quotes. Then we'll add one more.
> 
> irb(main):006:0> input3 = "'''Jimbo' said, 'this isn''t too hard'.''"
> => "'''Jimbo' said, 'this isn''t too hard'.''"
> irb(main):007:0> input3.gsub( /(\A|[^'])'('')*([^']|\Z)/, "\\1''\\2\ 
> \3" )
> => "''''Jimbo'' said, ''this isn''t too hard''.''"
> 
> 
> (The above could be made a bit simpler with lookaheads and  
> lookbehinds. I've chosen not to use them because you need Oniguruma  
> to do lookbehinds, and no sense cluttering the example with one  
> technique for the front and another for the back.)
> 
> 

I've been fighting to figure out how a regexp should look, so I appreciate very much your approach. 
I will be reading it carefully.

thanks,

./alex
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