Which of the following is not a filter command? A. sort B. wc C. grep D. cat E. None of the above

The correct answer is: D. cat

A filter command is a command that takes input from a file or standard input and produces output based on some criteria. The criteria can be specified using options or by piping the output of one command to another.

sort sorts the lines of a file in alphabetical or numerical order.
wc counts the number of lines, words, and characters in a file.
grep searches a file for lines that match a regular expression.
cat concatenates files or standard input and prints them to standard output.

cat is not a filter command because it does not produce output based on any criteria. It simply prints the contents of a file or standard input to standard output.