From: Edwin Fine <efine145-nospam01@...>
Date: 2006-11-24T02:43:55+09:00
Subject: Re: double-slashes in input causing trouble

Hugh Sasse wrote:
> On Fri, 24 Nov 2006, Jeremy Wells wrote:
> 
>         [...]
>>    original_section = $1
>>    new_section = bit_at_top + original_section
>>    new_body = body.sub(original_section, new_section)
>      new_body = body.sub(Regexp.new(Regexp.quote(original_section)),
>                                            new_section)
>> 
>>    File.open(input,'w') do |file|
>>       file.write new_body
>>    end
>> end
> 
>         # Hugh

Makes no difference. String#sub states that metacharacters in the 
pattern will not be interpreted if the pattern is a String and not a 
Regexp.

Check it out:

irb(main):061:0> x
=> "section 
header\nkjhKAJSHDKjashdkjASH\\\\\\\\\\\\\\\\KJahfdkasjhdfkajshdfjh\nsection 
footer"
irb(main):062:0> y
=> "\nkjhKAJSHDKjashdkjASH\\\\\\\\\\\\\\\\KJahfdkasjhdfkajshdfjh\n"
irb(main):063:0> z
=> "xyzzy 
\nkjhKAJSHDKjashdkjASH\\\\\\\\\\\\\\\\KJahfdkasjhdfkajshdfjh\n"
irb(main):064:0> x.sub(y,z)
=> "section headerxyzzy 
\nkjhKAJSHDKjashdkjASH\\\\\\\\KJahfdkasjhdfkajshdfjh\nsection footer"
irb(main):065:0> x.sub(Regexp.new(Regexp.quote(y)),z)
=> "section headerxyzzy 
\nkjhKAJSHDKjashdkjASH\\\\\\\\KJahfdkasjhdfkajshdfjh\nsection footer"

Identical results.

The problem is that the backslashes in the REPLACEMENT string are being 
interpreted.

The way to overcome this is to use the block form of sub:

new_body = body.sub(original_section) {|s| s = new_section}

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