The Shell

reading

We will loosely follow the Software Carpentry lesson on The Unix Shell

The shell

The shell is your interface to the operator system. It implements a REPL interface: Read, Execute, Print, Loop. This means it:

• Reads: Bash will read a command that you enter at the promot

• Executes: Bash will execute the command

• Prints: the output from the command will be printed to the terminal

• Loops: the process repeats, with the prompt waiting to read your next command.

The power of the shell is that we can easily combine different tools together to create powerful commands to manipulate files on the computer.

Accessing the shell

To access the shell, we need to open a terminal on the computer. This will present us with the command prompt, which typically is a $ (although it can be customized)`.

We already saw the echo command:

echo Hello, World

But there are many more commands that we will learn shortly.

Which shell?

There are a wide variety of shells that are used today. The default on many systems is BASH. Others that you might commonly encounter are zsh and fish.

We’ll focus on BASH, and most of what we learn here will apply directly to the other shells.

Some online shell documentation:

• The Software Carpentry Unix Shell lesson

• The official Bash Reference Manual

A basic “cheat sheet” is available here: Unix/Linux Command Reference.

Configuring Bash

Every time we open a terminal, the shell reads a special file called .bashrc. This file contains commands that customize our shell in various ways.

As the semester goes on, we’ll add to this file to make our lives easier.

We can look at the current contents of our .bashrc file by doing:

cat ~/.bashrc