How to "force" a file's ISO-8859-1ness?
I remember when I used to develop website in Japan - where there are three different character encodings in currency - the developers had a trick to "force" the encoding of a source file so it would always open in their IDEs in the correct encoding.
What they did was to put a comment at the top of the file containing a Japanese character that only existed in that particular character encoding - it wasn't in any of the others! This worked perfectly.
I remember this because now I have a similar, albeit Anglophone, problem.
I've got some files that MUST be ISO-8859-1 but keep opening in my editor (Bluefish 1.0.7 on Linux) as UTF-8. This isn't normally a problem EXCEPT for pound (£) symbols and whatnot. Don't get me wrong, I can fix the file and save it out again as ISO-8859-1, but I want it to always open as ISO-8859-1 in my editor.
So, are there any sort of character hacks - like I mention above - to do this? Or any other methods?
PS. Unicode advocates / evangelists needn't waste their time trying to convert me because I'm already one of them! This is a rickety older system I've inherited :-(
PPS. Please don't say "use a different editor" because I'm an old fart and set in my ways :-)
Answer
Normally, if you have a £ encoded as ISO-8859-1 (ie. a single byte 0xA3), that's not going to form part of a valid UTF-8 byte sequence, unless you're unlucky and it comes right after another top-bit-set character in such a way to make them work together as a UTF-8 sequence. (You could guard against that by putting a £ on its own at the top of the file.)
So no editor should open any such file as UTF-8; if it did, it'd lose the £ completely. If your editor does that, “use a different editor”—seriously! If your problem is that your editor is loading files that don't contain £ or any other non-ASCII character as UTF-8, causing any new £ you add to them to be saved as UTF-8 afterwards, then again, simply adding a £ character on its own to the top of the file should certainly stop that.
What you can't necessarily do is make the editor load it as ISO-8859-1 as opposed to any other character set where all single top-bit-set bytes are valid. It's only multibyte encodings like UTF-8 and Shift-JIS which you can exclude them by using byte sequences that are invalid for that encoding.
What will usually happen on Windows is that the editor will load the file using the system default code page, typically 1252 on a Western machine. (Not actually quite the same as ISO-8859-1, but close.)
Some editors have a feature where you can give them a hint what encoding to use with a comment in the first line, eg. for vim:
# vim: set fileencoding=iso-8859-1 :
The syntax will vary from editor to editor/configuration. But it's usually pretty ugly. Other controls may exist to change default encodings on a directory basis, but since we don't know what you're using...
In the long run, files stored as ISO-8859-1 or any other encoding that isn't UTF-8 need to go away and die, of course. :-)