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Subject: Re: [PHP-DEV] preg_replace does not replace all occurrences
From: mail_ben_schmidt@yahoo.com.au (Ben Schmidt)

> Now, here is a pattern which actually means "a quote which doesn't
> already have a backslash before it" which is achieved by means of a
> lookbehind assertion, which, even when searching the string after the
> first match, "'str", still 'looks back' on the earlier part of the
> string to recognise the second quote is not preceded by a backslash and
> match a second time:
>
> /(^|(?<!\\))'/
>
> As a PHP single-quoted string this is:
>
> '/(^|(?<!\\\\))\'/'

And I should mention, as Martin did, that this actually isn't a good
idea. There are better/safer ways to escape quotes. In particular,
consider how this subject string

    str\\'; delete from users;

will not have the quote escaped, because it is preceded by *two*
backslashes. To match more carefully, you have to be careful to 'eat
backslashes in pairs'. Someone gave a pattern that attempted to do
something like that in an earlier post, too.

Ben.