---
title: Beginner Lab 2 - Core Shell
layout: lab
---

Welcome to Lab 2! In this lab you will be learning how to work productively in a shell.

Don't forget to use Google and `man` when stuck. The resources linked at the bottom may be helpful as well.

![XKCD 1319](https://imgs.xkcd.com/comics/automation.png)

## Setting up
This lab requires a bash shell, `vim`, and `tmux`.
If you do not have tmux: `apt-get tmux`

## SSH (Secure Shell)
SSH allows you to log in to a remote computer through the internet.
It is the equivalent of opening a shell on a remote computer.

The usage is `ssh [remote username]@[remote host]`.

### Question
1. Log on to `tsunami.ocf.berkeley.edu` with your OCF username and password. There is a file in `~staff/public_html/decal`. Open it. What is the secret in the file?


## Pipes and Redirection
Chaining together commands is essential to automating your way through the shell. Here's a quick cheat sheet:

`>` : Redirect stdout to a file.

`>>` : Append stdout to a file.

`<` : Read input from a file.

`|` : Send output from one program to the input of the next.

### Questions
1. What line could you use to save the first 10 lines of a file that do not contain any vowels to a new file called `return.txt`? 
2. How could you write `cat output.txt | grep "Cal"` without using a pipe? (Hint: Use a temp file)

### Other useful tricks
`!!` can be used to repeat the previous command in the shell.

E.g. 
```
python program.py = python program.py
sudo !!           = sudo python program.py
```

`!:[num]` is treated as the previous command's [num] argument. 

E.g.
```
touch doc.txt = touch doc.txt
vim doc.txt   = vim !:1
```

Note: This behavior is from bash and some other shells that implement it.

## A quick intro to `vim`
### Why `vim`?
 - It's a descendant of vi, which was written in Berkeley by Bill Joy, who went on to found Sun Microsystems.
 - Sometimes you will be suddenly thrown into `vim` via merging git conflicts or other programs.
 - It's included in practically every UNIX environment.
 - You can be very productive when familiar with it.

### Hello World
     Vim is a modal text editor, meaning that you can change editing modes in order to do different things. There are 3 primarily used modes: **Normal**, **Insert**, and **Visual** mode.
#### Normal mode:
 - Used for moving around and editing text
   - `hjkl` to move left, up, down, and right
   - `G` to move to end of file, `gg` to move to beginning
   - `i` to enter **i**nsert mode (`a`, `o` also change mode in different ways)
   - `dd` to cut a line
   - `yy` to copy a line
   - `p` to paste
   - `/` to search
   - `u` to undo
 - Type in commands with `:`
   - Save with `:w`
   - Exit with `:q`
 - Explore more commands online!

#### Insert mode:
 ![Example](https://d26aqo05ggejx9.cloudfront.net/i.gif)
 - Used for editing text like a usual editor
 - Arrow keys to move
 - Esc to exit to normal mode (lots of people bind it to Caps Lock)

#### Visual mode:
 - Enter with `v` from normal mode
 - Used to select text visually
 - Modify selection with normal mode movement commands
 - Use `o` to move the cursor to the other side of the selection
 - Yanking, deleting, and pasting use `y`, `d`, `p` (sound familiar?)

  A key feature of `vim` is **chaining together commands**.
  Normal mode is essentially a massive amount of shortcuts that you can combine to quickly navigate and edit a file.
  Want to move down 3 lines?
  You know that `j` means move down 1 line, so you can use `3j` to move down 3.
  `d` is for deletion and `w` is to jump to the next word, so what does `dw` do?

### Questions
 Try playing around with [lab2.md](https://github.com/tanx16/decal-web/blob/master/labs/b2.md) while looking up some new commands. Use `wget` to download it!
 - How would you delete the previous 10 lines?
 - How would you jump back to the shell without exiting `vim`?
 - How would you edit a new file alongside another file?
 - How would you indent a block of text?

### If you're interested in `emacs` instead
 - Use [this](http://readline.kablamo.org/emacs.html) cheatsheet

## A quick intro to tmux
 ![Example](https://lightrains.com/assets/img/blog/tmux-tips.png)
### Why tmux?
 - You can open multiple windows when sshed into a machine.
 - You can go compile and run programs while editing them.
 - You can logout and ssh back in without having to reopen all your files.

### Getting Started:
 - Start a session with `tmux`.
 - Detach from a session with `Ctrl-b d` (press d after releasing `Ctrl-b`)
 - Split into 2 panes with `Ctrl-b %` (vertical) and `Ctrl-b "` (horizontal)
 - Swap current pane with `Ctrl-b o`

### Question
 - Take a screenshot of a tmux session with multiple windows, panes, and a named window with your username. 

### Advanced usage (optional)
 - Tmux can be used to share your session with others.
 - Try remapping shortcuts like the prefix `Ctrl-b` to something more convenient.
 - `Ctrl-b [` can be used to scroll around buffers and copy things.

### Checking off
 Once you're done remember to fill out the [check off form](goo.gl/rDqwi7).
 There are multiple valid answers for some of the questions.
 Don't be stressed about getting something exactly correct.
 Please answer the feedback questions if there's anything you want to say!

### Resources
 [Keybindings](http://teohm.com/blog/shortcuts-to-move-faster-in-bash-command-line/)

 [Learning vim progressively](http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/)

 [Tmux cheat sheet](https://gist.github.com/MohamedAlaa/2961058)