sponge

n. [Unix] A special case of a filter that reads its entire input before
writing any output; the canonical example is a sort utility. Unlike most
filters, a sponge can conveniently overwrite the input file with the output
data stream. If a file system has versioning (as ITS did and VMS does now)
the sponge/filter distinction loses its usefulness, because directing filter
output would just write a new version. See also slurp.

