From: Paul Battley <pbattley@...>
Date: 2006-07-29T08:10:09+09:00
Subject: Re: Finding "\" in a string

On 28/07/06, Eric Armstrong <Eric.Armstrong@sun.com> wrote:
> Very helpful. At least now I have a good idea that it
> can be made to work. Now let's see if I can dial in my
> understanding with respect to replacement strings...
>
> The fact that \1, \2 are recognized /shouldn't/ matter,
> because the tokenizer really ought to ignore any \x
> sequence where the x isn't a known special character.
> But it's rapidly becoming apparent that the tokenizer
> takes any \x and translates it to /something/, so we
> need \\ to get one \ in the string.

In fact, the tokenizer *does* ignore non-special sequences:

"\\foo".gsub("\\", "\\x") # => "\\xfoo"

And if there's nothing else left in the string, that works, too:

"\\foo".gsub("\\", "\\") # => "\\foo"

However, in order to be able to produce a literal \1, it also needs to
understand \\. Therefore, this gives the same effect:

"\\foo".gsub("\\", "\\\\") # => "\\foo"

But I missed a trick earler. We only actually need six backslashes to
emit two: the end of the string will terminate the sequence as in the
second example:

"\\foo".gsub("\\", "\\\\\\") # => "\\\\foo"

Is it getting clearer?

Paul.