So, I realize that things get more complex when you start extending the length of your "context" (though I will argue that in a lot of these cases the result is wrong anyway, so attempts to make it less wrong are weird: you can't, for example, match XML with a regex, so if you are doing that at all I'm expecting you are at a command line trying to do some quick grep and sed filtering, in which case there are some really really easy solutions at hand that are going to be fine), but... this article starts with the premise that the default solution to this is somehow lookaround, but lookbehind in paticular is a feature you aren't given often enough that it is worth avoiding it, and it is easy to do so in this case: '((?!"Tarzan").|^)Tarzan'. Though like, "real talk": does whatever random tool you are using even have lookahead? The reality is that lookaround is convenient, and I've totally gotten lost in its intricacies a long time ago, but this is such a simple case that it seems worthwhile to appreciate how it works and how the underlying expressions manifest... and then like, I can appreciate that the "trick" the author is advocating for is easily extensible to multiple "contexts" (which I keep putting in quotes, as if we are honest about this being "context" then you can't solve it with a true "regular expression"... we are kind of half-assing this by not realizing that the middle Tarzan in '"Tarzan"Tarzan"Tarzan"' is not actually enclosed in quotes), but it is even less useful than the lookaround variants (which are at least supported by grep -P)... how am I supposed to pass the article's recommendation to grep, much less grep -l? If we are somehow required to solve this problem with a single regular expression (which is totally an acceptable limitation, as that's what makes using grep -l complex: doing multi-stage filtering is annoying), my recommendation thereby would be to simply do: '([^"]|^)Tarzan|"Tarzan([^"]|$)'. This doesn't require any fancy features, and I think is thereby much easier to explain than anything you can find in this article (including the author's "trick"). If you don't have to do it in a single pass, then do it in two: grep 'Tarzan' | grep -v '"Tarzan"' (which is sloppy, but again: you can't actually do this task using regular expressions anyway, so sloppy is fine: look at the result and verify it makes sense... under no circumstances should you code stuff like this for automated use in production, though, which is then scary as the author's "trick" is really only applicable to sitting around in a heavier language, meaning they might not understand that this is all flawed by definition).
