[_swa8]

Since I develop backup software, this is a problem I needed to solve (e.g., for verifying that restore works). So I wrote a tool: http://liw.fi/summain/

It produces output that is meant to be usefully diffable.

[voltagex_]

That's a neat looking application - bonus points for a good manpage, too.

That said, how does it handle firstpath/somefile.bin and secondpath/somefile.bin being identical? This breaks your "diffable" output because the paths are different.

[_swa8]

You run it in such a way that the paths are identical. For example, by using the -r option.

$ mkdir foo

$ echo foo > foo/bar

$ cp -a foo foo2

$ summain -r foo > foo.summain

$ summain -r foo2 > foo2.summain

$ diff foo*.summain