Which of the following is not a communication command. A. write B. mesg C. mail D. grep E. None of the above

The correct answer is D. grep.

Write, mesg, and mail are all communication commands. Write allows you to send a message to another user on the same system. Mesg allows you to control whether or not you are receiving messages from other users. Mail allows you to send and receive messages to and from other users on the system or on other systems.

grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. It is not a communication command.