Replacing text except in the URL - ruby

Question

Say that we have the following text
example abc http://www.example.com
I know how to replace example by some text for instance. But, when I do that, how can I tell the program NOT to substitute the example in the URL?

Answer 1

UPDATE
#kiddorails reminded me of a known trick to work around a missing variable-width look-behind that can be implemented in Ruby as well. However, the regex used by #kiddorails will not replace example before the URL. Also, it is not dynamic.
Here is a function that will replace specific words (whole word mode is enforced by using \bs, but they can be removed in case you need to match strings with non-word leading and trailing characters) not in an URL even if they contain symbols that must be escaped in a regex:
def removeOutsideOfURL(word, input)
rx = Regexp.new("(?i)\\b" + Regexp.escape(word.reverse) + "(?!\\S+ptth\\b)")
return input.reverse.gsub(rx,"").reverse
end
puts removeOutsideOfURL("example", "example def http://www.example.com with a new example")
Output of a sample program:
def http://www.example.com with a new
ORIGINAL ANSWER
For this concrete example and context, you can use (?<!http:\/\/www\.)example/:
puts "example def http://www.example.com".gsub(/(?<!http:\/\/www\.)example/, '')
>> def http://www.example.com
Demo on IDEONE
You can add more look-behinds to set more conditions, e.g. /(?<!http:\/\/www\.)(?<!http:\/\/)example/ to also keep example straight after http://.
Or, you can also check for periods on both ends:
(?<!\.)example(?!\.)

Answer 2

You can use sub:
"example def http://www.example.com".sub("example","")
Result:
" def http://www.example.com"

Answer 3

Update: Pointers by #stribizhev :)
For this particular use case, I will go along with negative lookbehind regex as #stribizhev used above.
But there is one gotcha with negative lookbehind regex - It only accepts fixed length regex.
So, if urls are like: http://example.com or http://www.example.com, the check can either pass for first case or last.
I suggest this approach - reverse the url, use negative lookahead regex and substitute reverse of "example" in your string. Here is the demo below:
regex = /elpmaxe(?!\S+ptth)/
str1 = "example http://example.com"
str2 = "example http://www.example.com"
str3 = "foo example http://wwww.someexampleurl.com"
str4 = "example def http://www.example.com with a new example"
[str1, str2, str3, str4].map do |str|
str.reverse.gsub(regex, '').reverse
end
#=>[" http://example.com",
" http://www.example.com",
"foo http://wwww.someexampleurl.com",
" def http://www.example.com with a new "]