What is a unix filter?
A unix filter is a program that reads data from standard input, writes data to standard output, and logs to standard error. (Some definitions do not include logging to standard error — YMMV.) Anyone who has spent time on the command line in a terminal has worked with unix filters.
Questions
What makes the unix filter a powerful concept for processing data?
What cool things have you done with unix filters?
How can you turn any unix filter into a network server?
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