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Worksheet: pushd and popd

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This worksheet corresponds to this chapter of the Command Line Crash Course.

Thinking with stacks

Before we jump into command line stuff, we have to talk about stacks.

A stack is a computer science concept. It is a data structure that you can imagine as a stack of paper on a table. You add new things to the top of the stack, one by one, and you remove things from the top of the stack, one by one.

When you add things to the stack, it's called "pushing," and when you remove things, it's called "popping."

Because we only manipulate the stack from the top, it's called a last-in-first-out (LIFO) data structure.

Exercise 1: consider the following series of events.

I have a stack that looks like this:

 baz     <- top
 bar
 foo
-----    <- bottom

Now I do the following things:

  1. push bat
  2. pop
  3. push zim
  4. pop
  5. pop
  6. push grr
  7. push dib
  8. push gaz
  9. pop

What does the stack look like now?

Additional notes:

Exercise 2: use the original stack from Exercise 1.

Pop three times. What does the stack look like now?

Additional notes:

Pop again. What happens?

Additional notes:

Apply this knowledge to pushd and popd

Let's switch gears. Above, we were talking about stacks and stack operations (push and pop) in general. As you migh imagine, the Bash commands pushd and popd use a stack in order to work.

If the command pwd means "print working directory," what does pushd mean? What does popd mean?

In 10 words or less, what does pushd do?

Does pushd take an argument?

If so...

What is it (give an example) and what does it do?

Additional notes:

Is it optional?

If so, what happens if you don't give an argument?

Additional notes:

If not, why not?

Additional notes:

In 10 words or less, what does popd do?

Does popd take an argument?

If so...

What is it (give an example) and what does it do?

Additional notes:

If not, why not?

Additional notes:

Explain the output pushd and popd give back to you

Additional notes:

Do pushd and popd take any options?

Additional notes: