What is the opposite of 'printf'?

[Matthew Woehlke]

(Sorry this isn't exactly the right list, but this feels like a problem 
coreutils should solve, and I don't see gmane carrying anything better.)

I am looking for a way to convert binary data to a format that 'printf' 
will understand (and more importantly, from which '<something> | sed 
's/\\/\\\\/g' | xargs printf' will produce the same output as the 
input). Am I missing such a utility, or might this be an opportunity for 
me to write 'unprintf' for coreutils? ('od -An -c' gets close, but still 
needs some complex parsing if it is to round-trip.)

The objective is to be able to reproduce a binary file from an 'editor 
friendly' shell script. I know base64 could do this, except that base64 
is not portable (even to pre-6.x GNU coreutils), whereas printf is IIRC 
required by POSIX.

--
Matthew
"Lost a planet, Obi Wan has? How embarrassing..."
 -- Yoda (Star Wars II: Attack of the Clones)