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Library Carpentry: The Unix Shell
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<h1>What is the shell?</h1>
<p>Last updated on 2023-05-08 |
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<h2 class="card-header">Overview</h2>
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<h3 class="card-title">Questions</h3>
<ul><li>What is the shell?</li>
<li>What is the command line?</li>
<li>Why should I use it?</li>
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<h3 class="card-title">Objectives</h3>
<ul><li>Describe the basics of the Unix shell</li>
<li>Explain why and how to use the command line</li>
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<section><h2 class="section-heading" id="introduction-what-is-the-shell-and-why-should-i-use-it">Introduction: What is the shell, and why should I use it?<a class="anchor" aria-label="anchor" href="#introduction-what-is-the-shell-and-why-should-i-use-it"></a></h2>
<hr class="half-width"><p>If you’ve ever had to deal with large amounts of data or large
numbers of digital files scattered across your computer or a remote
server, you know that copying, moving, renaming, counting, searching
through, or otherwise processing those files manually can be immensely
time-consuming and error-prone. Fortunately, there is an extraordinarily
powerful and flexible tool designed for just that purpose.</p>
<p>The shell (sometimes referred to as the “Unix shell”, for the
operating system where it was first developed) is a program that allows
you to interact with your computer using typed text commands. It is the
primary interface used on Linux and Unix-based systems, such as macOS,
and can be installed optionally on other operating systems such as
Windows.</p>
<p>It is the definitive example of a “command line interface”, where
instructions are given to the computer by typing in commands, and the
computer responds by performing a task or generating an output. This
output is often directed to the screen, but can be directed to a file,
or even to other commands, creating powerful chains of actions with very
little effort.</p>
<p>Using a shell sometimes feels more like programming than like using a
mouse. Commands are terse (often only a couple of characters long),
their names are frequently cryptic, and their output is lines of text
rather than something visual like a graph. On the other hand, with only
a few keystrokes, the shell allows you to combine existing tools into
powerful pipelines and to handle large volumes of data automatically.
This automation not only makes you more productive, but also improves
the reproducibility of your workflows by allowing you to save and then
repeat them with a few simple commands. Understanding the basics of the
shell provides a useful foundation for learning to program, since some
of the concepts you will learn here—such as loops, values, and
variables—will translate to programming.</p>
<p>The shell is one of the most productive programming environments ever
created. Once mastered, you can use it to experiment with different
commands interactively, then use what you have learned to automate your
work.</p>
<p>In this session we will introduce task automation by looking at how
data can be manipulated, counted, and mined using the shell. The session
will cover a small number of basic commands, which will constitute
building blocks upon which more complex commands can be constructed to
fit your data or project. Even if you do not do your own programming or
your work currently does not involve the command line, knowing some
basics about the shell can be useful.</p>
<p><em>Note to Lesson Instructor: Consider providing an example here of
how you’ve used the Unix shell to solve a problem in the last week or
month</em></p>
<div class="section level3">
<h3 id="where-is-my-shell">Where is my shell?<a class="anchor" aria-label="anchor" href="#where-is-my-shell"></a></h3>
<p>The shell is a program that is usually launched on your computer much
in the way you would start any other program. However, there are
numerous kinds of shells with different names, and they may or may not
be already installed. The shell is central to Linux-based computers, and
macOS machines ship with Terminal, a shell program. For Windows users,
popular shells such as Cygwin or Git Bash provide a Unix-like interface,
but may need to be installed separately. In Windows 10, <a href="https://docs.microsoft.com/en-us/windows/wsl/install" class="external-link">the Windows
Subsystem for Linux</a> also gives access to a Bash shell command-line
tool.</p>
<p>For this lesson, we will use Git Bash for Windows users, Terminal for
macOS, and the shell for Linux users.</p>
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<ul><li>The shell is powerful</li>
<li>The shell can be used to copy, move, and combine multiple files</li>
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