From: sera@... (Francis Hwang)
Date: 2004-05-13T09:48:53+09:00
Subject: nasty regexp problem

Hi all,

I discovered a strange bug in Lafcadio which I'm trying to work out,
but the regexp is getting really nasty. Basically, to commit text
values to the database I need to double any apostrophe, except those
that are preceded by a backslash. This has to account for apostrophes
at the beginning of the string, and multiline strings where the
apostrophe is at the start of a new line. Examples would be:

"I can't drive 55" -> "I can''t drive 55"
"Don\'t escape here" -> "Don\'t escape here"
"'" -> "''"
"line 1\n' line 2" -> "line 1\n'' line 2"

So here's the regexp that does it:

value = value.gsub( /(^|[^\\\n])'/ ) { $& + "'" }

which works fine, except I just discovered that it fails in one odd
case:

"'''" -> "'''''"

(That is, a single line of three apostrophes should become six
apostrophes, but instead it becomes five.)

Any idea why this is doing it? I suspect I'm being too clever by
including the beginning of line in a grouping, and maybe that affects
how the regexp is processing the string?

F.