:sponge: [UNIX] n. 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}.
-- The AI Hackers Dictionary
filter: [orig. {{UNIX}}, now also in {{MS-DOS}}] n. A program that
processes an input data stream into an output data stream in some
well-defined way, and does no I/O to anywhere else except possibly
on error conditio...