How to Computers

Jump to: - How to Terminal - How to git and GitHub - How to python - How to SSH

---

How to Terminal

Files and Directories

A file is an entity that stores information. A directory is a folder, holding other files and directories within itself. There is a root directory (/) from which all files, directories, and programs are stored on your computer.

Recursive

A directory can contain multiple files and/or multiple directories that each have multiple files and/or directories. If a command or program is "recursive," it will act on a directory and all of the contents of that directory

Scripts

A script is a list of a particular sequence of commands, usually stored in a file or saved for future reference

Leaving Comments

The # symbol followed by a string can be used to leave a comment in a script that will be skipped over by the shell, so that it won't run as a command. This can be useful for leaving notes on what your command does for others or for future reference

The Shell

The shell, also known as the terminal or command line, is a program that enables users to direct commands to the computer to do. The computer reads those commands and then runs programs to achieve your specified task. The most common way people do this is through a graphical user interface (GUI), where one can click icons and use menus to interact. Here however, you will use a command line interface (CLI), where one can type commands in a scripting language.

Shell Prompt and Basic Structure of a Command

The shell's prompt $ is where a command/executable is entered. This may look different depending on your device and operating system, but the shell waits for your input here:

$ CommandName [option(s)] [argument(s)]

• an option changes the behavior of a command
• an argument states what the command should operate on
• parameters are options and arguments
• commands can have none or more than one option and argument

Key Commands

Note: each command can have several options with combinations of arguments, not listed here. Explore them to fully access the shell's capabilities.

Command	Description
$	Command Line Prompt - the shell waits for your inputted command here
pwd	Print Working Directory -at any point in time in the shell we are in a directory -this will print the current working directory (and hence the path to it)
cd	Change Directory Do: $ cd [path] to change from the current working directory to specified path
ls	List - lists contents of a directory
ls --help	List Help Option - the --help option lists all options that can be used for ls - useful to reference
cat	Catalogue - prints contents of a file
clear	Clear - clears all text on terminal
mkdir	Make Directory Do: $ mkdir [path] to name and create a directory
rmdir	Remove Directory Do: $ rmdir [path] to delete a directory
touch [path]	Create File - creates a file
rm [path]	Remove -deletes specified file -does not ask to confirm deletion; once deleted, deleted forever
mv [old] [new]	Move - moves [old] contents to [new] contents - expects last option to be a directory - can be used to rename files via same structure
cp [old] [new]	Copy - copies files from [old] to [new] where [new] is the location you are copying to - you can change the name of the new file at the step as well
wc	Word Count - counts the number of lines, words, and characters in files, and prints those values in that order
|	Pipe - feeds the output of one command as the input for another command Ex:$ echo MyNovel.txt | head -n 15 -first command would print the text file MyNovel.txt in its entirety but redirects that as the input for the command on the right of | - head -n 15 prints the first 15 lines of its input (MyNovel.txt) so in the end only the first 15 lines of MyNovel.txt will be printed in the shell
>	Redirect - redirects output or input of a command to a file - overwrites what's in the destination file
>>	Redirect - redirects output or input of a command to a file - appends output to what is already in the destination file
head	Head - prints by default the first 10 lines of one or more files
tail	Tail - prints by default the last 10 lines of one or more files
sort	Sort - sorts lines of text in a file as specified by options - by default sorts by reverse alphanumeric order so that: - a line starting with a number is listed first, then ones with letters
cut	Cut - removes or cuts out sections of a specified file or data
echo	Echo - prints text or strings
nano	Text Editor Program Do: $ nano [file] to edit a text file via nano - save and exit the nano program to return to the shell screen
uniq	Uniq - removes adjacent duplicate lines in a file
history	History - lists all commands, numbered, from the start of the session in the shell - history command is printed last - useful to repeat previous work
grep [pattern] [path]	Grep - searches for a continuous string in one or more files that match a pattern - case insensitive unless specified
find [path]	Find - finds and prints every file and directory under the specified path and parameters given in the command

Keyboard Shortcuts

Shortcut	Description
↑↓	Use the arrow keys on your keyboard at the prompt to scroll through previous commands, one line at a time, instead of scrolling through the terminal with your mouse
Ctrl + A	Use to navigate to the beginning of a line
Ctrl + E	Use to navigate to the end of a line
Tab	Use Tab Completion to automatically fill in the name of a file or directory instead of manually doing so Note: if mulitple file or directory names are named similarly in the beginning of their title, the tab completion key won't work until the name is unique Ex: If there are text files MyNovelBeg.txt MyNovelMid.txt and MyNovelEnd.txt and we want to type MyNovelBegEnd.txt tab completion will work until MyNovelE is typed and the Tab key is pressed
~	-the tilde represents the user's home directory -can be used to navigate directories without typing out the user's home directory
* or ?	Wildcards -a character that can be used to represent a set of none or more characters -can be used for ease of navigating files and directories in the shell

(back to top)

---

How to git and github - Using a Version Control System

Key concepts

Version Control Systems

A version control system is a tool for managing changes to a file, so that multiple users can edit and contribute code to a shared file. Instead of copying the file multiple times for each user to then edit, there is one file, with its edit history recorded. Who contributed what, and when, is recorded as well. Independent users can record their contributions without committing those changes for review. The system will notify when there's a conflict between code. Note that the changes are separate from the original file. In this way, users changes to the files can be recorded and reviewed before they are taken as a real edit to the original file, allowing them to work in parallel without conflict.

Repository

A repository is the complete history of the changes made to a file that are specified to be reviewed. The repository can be kept in sync across multiple different computers. The history will be stored in your repository, usually ending in .git

Basic structure of a Git Command

git verb options: a git verb is a what we want git to do for us, and an option is more information that may need to be provided for the [verb] to complete the task we want it to do.

Remote vs. Local Repositories and Git Push and Pull

A local repository is the versions of your file that you have on your computer. A remote repository is the versions of the file that is hosted on a server that all persons contributing to the project can access. A git push is when you transfer your local repository to the remote repository. A git pull is done when you copy the remote repository to your local repository.

Setup

Git Configuration

Usually, this will only need to be done once. This step sets up your settings for using Git, such as forming your username and email that marks you as the one who is making your edits. Your preferred text editor, and whether or not you want to use these settings globally, is determined. Globally means these settings will be applied to all of your repositories.

SSH - Creating a Secure Key Pair

You will need to have a secure key pair between your local repository and the remote repository. There is a public key, and your unique individual key. If a public key has not been made, that must be done.

Working in a repository

Creating a Repository

Once you have configured Git, create the repository in which all versions of your file will be stored. This will be a directory. First navigate to the root project folder, then utilize git init to initate the directory as a repository.

$ cd [path to your root project folder]
$ git init

Avoid creating nested repositories. These are redundant, because when a repository is made, git tracks that directory, and all files and subdirectories in that repository. In fact, if a nested repository is made, the outer repository may attempt to act on the inner repository.

Example Walkthrough of Committing to git

Suppose you have made an edit to a text file git_commit_example and wish to commmit it. First add the new change you made to the staging area. This will ensure Git is tracking your change.

$ git add git_commit_example

Then commit this change. This means any changes made that were added will be committed. Ensure to leave a commit message to describe the changes you have made.

$ git commit -m [your commit message here]

A Good Commit Message: Leaving a commit message is useful for both yourself and others. Try to keep it less than 50 characters, and convey: "if applied, this commit will..." to accurately describe your changes.

Managing conflicts: Merging is the process of potentially combining your edits to the original file you were editing. If there are conflicts that compete or interfere with each other, GitHub will highlight this and not allow your code to merge. See this link to Github tutorial for beginners for additional information.

Text Editors: vim is the default text editor on many Git programs. There are numerous text editor programs you can use with Git that may need to be downloaded. You will use a form of git config that is specific to that text editor to install it.

Useful Commands

Command	Description
git log	this will list a log of all commits in the terminal, including the commit's unique ID identifier, date and time, and your commit message
git show	-similar to git log, this will show a log of commits and tags, but will also where HEAD is at currently
git status	displays the state of the staging area and your working directory, including if there's modifications or not
rm -rf	the rm command will remove files or directories, while the -rf parameter will remove a repository *use with caution, as this can delete a project!
git diff	-this show changes in your project -you can use this to compare commits or changes in your working directory for instance

Accessing Git Help Manual: git has a built in feature to access the git help manual, to view subcommands and to see options. This can be accessed by entering any of the following on the command line:

git config -h
git config --help
git help

(back to top)

---

How to python

Variables. You can assign a value as a variable to later work with. When you call the name of the variable, Python will substitute the value of that variable. To make a variable use the = sign. For instance: novel_wordcount = 35432 makes novel_wordcount a variable that has a value assigned to it.

Data types. Python works with data. Three common types are:

• integer: an integer value, such as 71, 2, or 965
• string: single or double quotes around text, such as 'this_is_a_string' or 34567
• float: fractional numbers expressed as decimals, such as 45.67 or 8976.11111

Functions. Python has a set of named functions that have instructions to perform a certain action when its name is typed in the command line. These are commands. One of the best uses of Python is for processing data. There are many different Python functions that can be used to interact with your data. This will depend on the program you are using. A function is a set of commands that will only be executed when called upon, following this format: You define the name of the function and parameters, and use return to state what you want done.

Libraries. Python has libraries which are units of code that perform certain tasks. These will need to be imported, providing us with more tools than basic python would. For instance, numpy reads and interprets data.

Counting + Arrays. Python starts counting from 0. This is important when referencing indices for arrays: ordered systems of values. An array will often depict data. In Python, an indice in an array is given by [row, column].

Commenting. The # symbol preceding a message is used for commenting, or lines that the shell will not interpret as a command.

Making Lists. When making a list of values, use a , to separate values, and enclose in []: [1, 2, 3, 4, 5]

Loops. Loops are a process that will repeat the same action over and over for unique values in a set or range. For loops are a type of loop, in a general pattern of: "for x variable, enact y on x" where x is a variable and y is a command. The loop will process each element in the list one at a time.

If Statements and Conditionals. Enabling an if statement means Python will only execute its given command if the conditions of the if statement are met.
if x and y means both x and y have to be true for the loop to execute.
if x or y means if x or y or both are true, the loop will execute its command.

Data Visualization: matplotlib. This is one of Python's most commonly used data visualization libraries. More uses than can be listed here are available, such as basic graphing and statistical measures, or grouping multiple plots together. This program is useful for processing large amounts of data. Explore it to access the library's full capabilities.

(back to top)

---

How to SSH

Depending upon your operating system, installation of SSH will vary. Once an SSH server is installed, you can start your connection. At the terminal line, type:

$ ssh your_username@your_ip_address

Enter your password. If it is your first time connecting, it will ask if you wish to continue connecting. Type 'yes' and press the enter key.

Now, you should be connected.

(back to top)