stcube is a very fast command that allows to perform basic statistics computation over many images, in a single command-line order: stcube *.fits.
stcube will return the min, max, mean, standard deviation, energy and absolute flux for all planes of all files given on the command-line. It works extremely fast, also for big images.
The median finder (stcube -m) is also very efficient, and useful to get an estimate of the background value in images of e.g. crowded fields.
stcube man page