PPOL 5203 Data Science I: Foundations

Command Line

Tiago Ventura

Why the Command Line?

When we are introduced to computers, we are often driven towards point-and-click usability. These are called Graphical user interfaces (GUIs). GUIs are great for many tasks, but they are not good for all tasks. GUIs work for what they were developed for. In that sense, it limits the way you interact with your computer condinational on the original development of the GUI at hand. If you need more, you need to speak directly to your operation system

The command line (CLI) is a program that allows you to interact directly with your operating system. So by using the command line, you have more control over all programs run in your machine. From the command line, you can run scripts, call programs like Python and R directly, and build all sorts of data pipelines.

For the purposes of our course, it'll help us:

  1. Understand file paths on your computer
  2. Serves as a common hub from which to work
  3. Allow for us to generate reproducible coding sequences (via running scripts)
  4. Streamline work flow
    • set projects up
    • work between languages
    • batch process heavy loads
  5. Vital when speaking to a computing cluster, working on a virtual machine, or ssh-ing into a local computer

Main Message: All this will come with time, and you will not finish the lecture today as a expert in CLI. The reason we start the course covering this 101 tool is that the command line will feature into our discussion on using git and also running Python programs.

Accessing the Command Line

The "command line" program can differ, however, given what machine you're running.

  • If you're on a Mac a unix command line comes installed on your machine. This is your terminal, which is an application available on all macs.

  • If you're on a Windows machine, you'll need to activate your Ubuntu terminal by turning on the developer mode on your computer. Instructions on how to do that can be found here. (Note that there are also other alternatives, such as putty)

    • Or really just ask ChatGPT on how to do this

For a more in-depth overview of the potential of Unix command line, see The Linux Command Line by William Shotts

Common command line commands

The following outlines a few common commands that will be useful as you move forward. Disclaimer: some of these commands may differ given your operating system, but it's only quick Google search to find out how things are done on your machine.

  • pwd: check working directory
  • cd <path>: change working directory
    • cd ..: go back to the last directory
    • cd ~: go to home directory
    • cd -: go back to where you once where
  • ls: list all files in the working directory
  • mkdir <dir name>: make a directory
  • mv <old path> <new path>: move file from old path to new path
  • cp <old path> <new path>: copy file from old path to new path
  • cat <file>: print the entire file
  • head: view the start of a file to some $N$ number of lines
    • head -n 3 file

  • tail: view the end of a file to some $N$ number of lines

    • tail -n 3 file

  • Making a file:

    • touch <file name>
    • echo 'text' > file

  • Renaming a File:

    • mv <old file name> <new file name>

  • Asking for help:

    • man <command name>
    • <command name> -h

  • Closing a command:

    • ctrl + z

  • Text Editor: vim or nano.

Introduction to vim

Vim is a text editor that runs in the terminal.

Basically, it is a note taker but built-in inside of your terminal. You need text editors to work with git and to submit scripts through the command line.

It is available on nearly all Unix systems, and highly extensible.

Open Vim

  • vim filename.txt: it opens a file in vim with the name filename.txt

Vim modes

  • Normal mode (default): for navigation and commands.

  • Insert mode: for typing text.

  • Command mode (via :): for saving, quitting, etc.

Writing in vim

  • Press i: insert text at cursor.

  • Just type now

Exit Insert Mode

  • Press Esc: back to Normal mode.

Save and Quit

  • :wq: write and quite

  • :q → quit without saving.

In [2]:
!jupyter nbconvert _basics_of_cmd.ipynb --to html --template classic

[NbConvertApp] Converting notebook _basics_of_cmd.ipynb to html
[NbConvertApp] Writing 280315 bytes to _basics_of_cmd.html