Forum: Ruby how to double single quote (beginner blockage)

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Alexandru P. (Guest)
on 2006-01-18 17:26
(Received via mailing list)
Hi!

Sorry for this `stupidĀ“ question but it looks like i am suffering a
mental blockage:

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

my `brainlessĀ“ attempt was:

[code]
fixed_value = ""
wrong_value.each_with_index do |char, idx|
	fixed_value << char
        	if ( (idx < wrong_value.size - 1)  && (wrong_value[idx + 1] !=
'\'') && (idx > 0) &&
(wrong_value[idx - 1] != '\''))
                	fixed_value << '\''
        	end
end
[/code]

but the above results in exactly the same strings. I would appreciate
very much your help

./alex
Jules J. (Guest)
on 2006-01-18 17:41
And what if the input string correctly contains double quotes?? ;-)

String doesn't have a each_with_index method.

class String
  def each_with_index
    counter = 0
    each_byte do |char|
      yield char, counter
      counter += 1
    end
  end
end

"abc".each_with_index do |char, index|
  puts char.chr + ' ' + index.to_s
end

Please note that char is an integer, so you have to call char.chr.

Untested, but it should work.
Alexandru P. (Guest)
on 2006-01-18 18:05
(Received via mailing list)
#: Jules J. changed the world a bit at a time by saying (astral
date: 1/18/2006 5:05 PM) :#
>     end
>
I have passed over my no-brainer moment:

[code]
fixed_value = ""
idx = 0
while (idx < wrong_value.size) do
	fixed_value << wrong_value[idx]
	if ( wrong_value[idx] == 39 )
		if ( (wrong_value[idx + 1] != 39) )
			if ( idx > 0 && wrong_value[idx - 1] != 39 )
				fixed_value << '\''
			end
		end
         end
         idx += 1
end
[/code]

but now i've reached the no-ruby point. Can you teach me what would be
the ruby way?

Note: the double quotes are not considered in this problem; in fact i am
removing them right from
the beginning

./alex
Gavin K. (Guest)
on 2006-01-18 18:05
(Received via mailing list)
On Jan 18, 2006, at 7:47 AM, Alexandru P. 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.)
unknown (Guest)
on 2006-01-18 18:27
(Received via mailing list)
On Thu, 19 Jan 2006, Gavin K. wrote:

> a single quote that has characters other than a single quote on either side,
> => "'Hey, it's al'alamein'"
> even-numbered runs.
>
> (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.)

nice explanation gavin.  my brain is too feeble for that but i do the
same
thing logically using

   irb(main):016:0> %Q( '''Jimbo' said, 'this isn''t too hard'.''
).gsub(/'+/){|m| m.size % 2 == 0 ? m : m << "'"}
   => " ''''Jimbo'' said, ''this isn''t too hard''.'' "

i assume it would be slower though.

cheers.

-a
Alexandru P. (Guest)
on 2006-01-18 18:33
(Received via mailing list)
#: Gavin K. changed the world a bit at a time by saying (astral
date: 1/18/2006 5:28 PM) :#
> to find a single quote that has characters other than a single quote
> => "'Hey, it's al'alamein'"
> always come in even-numbered runs.
>
>
> (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
Alexandru P. (Guest)
on 2006-01-18 18:33
(Received via mailing list)
#: Gavin K. changed the world a bit at a time by saying (astral
date: 1/18/2006 5:28 PM) :#
> to find a single quote that has characters other than a single quote
> => "'Hey, it's al'alamein'"
> always come in even-numbered runs.
>
>
> (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 (mainly the
first/last position part), so
I appreciate very much your approach. I will be reading it carefully.

... and what is Oniguruma? (sounds pretty cool :-) ).

thanks,

./alex
Jules J. (Guest)
on 2006-01-18 19:39
The new Regex library for Ruby 2.0?

Jules
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