Unix Lesson 2: The Shell
The "shell" is a command-line interface, meaning, to interact with it, you type into it, hit enter, and it responds back with results. It is what you see when you use the "Terminal". It is a very important part of using Unix properly.
There are several kinds of shells. We are going to focus on the "Bourne" shell, named after the Unix pioneer Stephen R. Bourne. Bourne shells start with a prompt, that usually contains the working directory, and a dollar sign to end the prompt, like so:
/foo/bar$
All things that you type will follow the $. After you are done entering your command, hit enter. When the shell is ready for more input, it will show the prompt again.
Commands & Parameters
The first word in the input to a shell is called a "command", and any words that follow it are "parameters" or "arguments"; they mean roughly the same thing. Parameters are separated by spaces. If you need to add a space to a parameter, use single or double quotes, 'like so'.
Examples
cat is a program that accepts filenames as parameters, then prints them to the screen. Our program, cat, is the command, and the filenames are the arguments.
cat foo.txtcat bar.txt foo.txtcat 'file with spaces.txt'
Meta-Characters
Since you can use the shell to write programs, the creators of the shell used special symbols, called "meta-characters", to make programming easier by typing less. These characters are nearly all non-alphanumeric (meaning, not a-z, A-Z, or 0-9) characters, including nearly all math symbols and even things like exclamation points! It's important to know because they can trip you up, but we will learn this at a later point.
Programming & Scripting
Shell "scripts" are programs that are stored in files that use the shell automatically. We will talk about these more later, just be aware when writing these scripts that you can also do much of it at the command-line interface as well. Sometimes this knowledge can be very handy!
An example of a program to use at the CLI (command-line interface, abbreviated), is a "program" that adds the file extension (the part of the end of a file name to determine what type it is) .foo to each file, then prints it without renaming it, in the working directory:
for i in * do echo $i.foo done
Since a semicolon (;) is equivalent to telling the shell enter was hit in most cases, you can also do:
for i in *; do echo $i.foo; done
And it will do the same thing in one line. Neat, eh?
Assignment
For each line, indicate the command and each parameter. Number the parameters.
cat foo.txtcat bar.wav foo.txtcat 'i love the shell.txt' foo.txtfoo bar.goo quux.baz