The trouble with using an option flag to printf(1) to toggle the meaning of %b is that you can't then mix format specifiers for binary literals and backslash escape expansion within the same format string. You'd just have to call printf(1) multiple times, which largely defeats the purpose of a format string.
I don't know what potential uppercase/lowercase pairs of format specifiers are free from use in any existing POSIX-like shell, but my suggestion would be settling on one of those to take on the meaning of C2x's %b. They'd still print '0b' or '0B' in the resulting binary literal when given the # flag, which might be a little confusing, but this seems like the safest way to go. It obviously still represents a divergence from C2x's printf(3), but I think the consensus is that that's going to happen regardless. ksh's format specifiers for arbitrary-base integer representation sound really slick, and I'd love to see that in Bash, too, actually. Zack
