Now that we have the command line set up and installed, we will go over a list of everyday commands that are considered the basics. Having a fundamental understanding of the basic commands will be the building block on which we'll learn the advanced commands found later in this book.
In this chapter, we will cover the following topics:
Woah... hold your horses, we need to cover some basics about commands. A command is a process run by a POSIX (Portable Operating System Interface) compliant OS (Operating System). OpenGroup maintains the standard in addition to it being ratified as an IEEE standard (http://pubs.opengroup.org/onlinepubs/9699919799/). In a POSIX environment, the process being run will have an environment, a current working directory, the command line (the path name that invoked the command and any arguments), and a series of file descriptors with stdin, stdout, and stderr (referred to by integer numbers 0, 1, and 2, respectively) being connected prior to handoff to your command.
Now with a little background and an installed command line, you are ready to go and we can actually start running commands. We will be going over some basic everyday commands. For those that are ready...
There's a couple of useful tricks for navigating the command line that, while optional, will improve your quality of life. This section has a selection of those tricks.
Bash, by default, saves the history of your commands. It will even save the history across sessions. This can be extremely useful because sometimes we make a small mistake and don't want to retype an entire command, or we want to repeat the same commands over and over. To see your history, type this command:
history
The following is what you should see on running the preceding command:
You can see that there is a numbered list of output commands. To repeat a numbered command, you can use the bang character, !. !<number> will repeat the number command verbatim:
!10
The following is what you should see on running the preceding command:
A double bang, !!, will repeat the...
As you can see, the command line is very powerful for everyday tasks. We learned how to do basic things, such as create files and directories, and navigate a system via the command line. We learned about manual pages, where to find help, and how to customize the shell.
In the next chapter, we'll take what you learned here and apply it against a real dataset. Feel free to come back to this chapter as it will be helpful throughout the rest of this book.
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