is a filter-like program that
consumes standard input but emits nothing to standard output. Again,
its actions on the input data are controlled only by startup
This interface pattern is unusual, and there are few well-known
examples. One is
the Unix print spooler. It will queue text passed to it on standard
input for printing. Like many sink programs, it will also process
files named to it on the command line. Another example is
in its mail-sending mode.
Many programs that might appear at first glance to be sinks take
control information as well as data on standard input and are actually
instances of something like the ed pattern
The term sponge is sometimes applied
specifically to sink programs like
that must read their entire input before they can process any of
The term ‘sink’ is traditional and common.