On Wed, 18 Dec 2019, Sven Schreiber wrote: The function form of printf() is not recommended, or even documented, but it is doing what it's supposed to (internally). The format-plus-arg leads to printing "a" (with four leading spaces but no trailing newline or space), then "eval" prints the return value from printf(), namely the number of bytes printed -- thus "a5", with the 'a' and the '5' contributed by different levels of code and just happening to be contiguous in the output. sprintf(), on the other hand, returns the constructed string itself, not the number of byes printed, so "eval" just gives four spaces followed by 'a'. Allin