Editing large files on Mac OS X

Have you tried Vim? It's the only editor I use :-)

Edit: It seems to depend upon a couple of factors. I used Vim with large CSV (i.e. text-based) files and that worked great. YMMV :-)

HexFiend is designed to read files of any size, but you'll need to work using fixed-column character wrapping and no newline detection.

If you just want to have an idea of structure, how about browsing with more or less?

Definitely vim is the answer. Check out the macvim, the mac version.

BBEdit, that old standby, is famous for handling really large files with aplomb (or, at least, it was back in the pre-TextMate era). There's a free version, TextWranger; I assume it's based on the same core and should still work.

I have used gvim for files larger than 1 GB of NASTRAN output. gvim handles large files very well. In fact that was the main reason I switched from Emacs to vim.

Emacs is a great editor but it can handle files only as large as 128 MB, at least the 32-bit version. If you decide to use Emacs I recommend to configure it to turn syntax highlighting off for large files.

Another way to deal with large files those days was heavy usage of head, tail and split.

emacs, naturally, at least a 64 bit build (you can do that on OS X now, right?)

But also, these are surely generated files. Do you really need to interact with them all at once?

Since you noted in a comment that it's actually an XML file and you just want to get an idea of its structure, you may want to check out Oxygen's LargeFileViewer, a helper app which is bundled with Oxygen XML Editor. (It might also come with Author, I don't know.)

Crisp claims the ability to edit files of "8GB or more", but I haven't tried it.