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.