It is impossible to know how many commands the average command-line citizen uses, but if we had to guess, we would place it at about 25. Some of these were introduced in Chapter 10, “Command-Line Quickstart,” but are covered here with greater depth. Others will be new to the reader. Still others are only mentioned in this list to give the reader ideas for further study. Here are some commands that every command-line user will want to learn:
cat—Prints the contents of a file
chmod—Changes file access ...