Looking for "diff"-like code to find differences between two files

[gft_robert at gsbacd.uchicago.edu]

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[sorry if this got posted multiple times, but it doesn't seem to show up at my
site]

I'm working on a project on the Mac in which we need to compare the text of two
files.  We need to do this on a character-by-character basis, not merely
line-by-line, because we need to go back and indicate which words/chars were
deleted and added.

I'm curious whether anyone has any code to suggest which does this.  Ideally we
need something which outputs some form of an ed script or something similar, so
that we can use this information in operating on the resulting difference file.

We were looking at the GNU diff routine, but from looking at the source it
seems that this may only output info on a line-by-line basis (we don't have the
man pages and haven't built it yet, so I don't know for sure).

While the resulting app may end up running under A/UX, basically it will be a
Macintosh app.  I'm posting this to the unix groups in the hope that there may
be a unix tool which we can adapt to our purposes.  Of course if someone has
some sample code which is not made for unix, that would be fine too.

One thing: the code should be able to handle large amounts of data.  Most of
our docs will be > 100 pages.

Any help/info very much appreciated!

Robert