Terminal Basics

What do terminals do?

Terminal's allow you to run binaries (compiled programs, sometimes called apps or programs) and scripts (sometimes called commands)

Example

Let's say you're on windows and you compilled a program called hello-world.exe, you can run this if you are in the same file-folder using:

hello-world.exe

you do not need the extension for binary files on windows, so you can also use

hello-world

Available terminals

*nix

I use *nix to mean any unix based system such as macos or linux

File paths

Used to locate files/folders. In order to run anything your terminal must know where the binary or script is. For example if you had a file called 'hello-world.exe' on the desktop you might use the filepath

/Desktop/hello-world.exe

Directory/dir/File folders

These are folders used to house files. They are typically denoted with either a \ or a / at the start or end. For example the desktop folder/directory would be /desktop or desktop/

Binaries/files

A file is just some data that is stored. A binary is something that is executable (can be run) like a program (when pathing to them the extension is usually optional). Binary files means a non-plain-text file that needs an application to view it properly (i.e. an image file).

Extensions

These denote the file 'type', it gives the OS an idea of what sort of content is inside the file. Please note this does not ENFORCE behaviour, just suggests it. So someone can open a file with an incompatible extension whenever they want. For example if you have a file called help.txt that would be a txt or text file with a filename of help. Some extensions have multiple dots such as tarballs which have the .tar.gz extension

Dotfiles

These are special file types that are JUST an extension. They are typically used for configuration and on windows can only be created by certain applications. An example would be a .gitignore file, which is a config file for git and the file is just .gitignore

OS Differences

Please keep in mind different operating systems use different standards, for example windows uses \ path seperators and *nix uses /. Likewise most systems folders are capitalized in windows (i.e. Downloads) and lowercase in *nix (i.e. downloads). There will be other differences I will try to point out as we go

Types of file paths

There are two types of file paths

Relative file paths

By default terminals will have a current working directory (cwd), this is what will be used as a starting point of reference to locate what you need from

Relative file path tricks

Here are some tricks for working with relative file paths (# is a comment)

. # Means cwd/current folder
.. # Means to go up one folder. (i.e. if cwd is /kieran/Desktop and you use .. it would be /kieran)

filename.extension # Because it's relative to the cwd you can just type files in the same folder as cwd
./filename.extension # Equivalent to the line above

folder # Because it's relative to the cwd you can just type the folder/dir if it's in the same folder as cwd
/folder # Equivalent to above, it's good practice to include a leading slash so others know it's a folder you're looking for
./folder # Equivalent to above

Wildcards

Wildcards (not always supported) allow you to say anything and everything (denoted with *), for example /Desktop/* means ANYTHING on the desktop or /content/*.md means all files that end in .md inside the /content directory. Or Desktop/development/* would be all files and folders inside /Desktop/development

Absolute file paths

These are file paths that DO NOT care about your cwd. They fully express EXACTLY where something is for example:

C:\Users\Kieran\Desktop\hello-world.exe

When using these you never have to worry about your CWD

When to use relative vs absolute

Use absolute when the path will never change (i.e. an installed application binary location)

Relative paths are better if your location may move. For example if you have a portable app that has a script then a relative path means you don't have to update the path every time you move it somewhere new

Cons of Absolute paths

Very long and hard to read, cannot dynamically update so if ANYTHING changes it breaks

Cons of relative paths

Can often trick you into a sense of safety where you forget which paths are being used and break something

There is a way to make absolute paths easier to work with

Environment variables

These are the state of the operating system you are running in. They can denote basically any form of state (you can also create env variables as a way of setting a sytem-wide config variable for an app)

Environment variables for paths

There is a built in env variable to find the home directory (directory where user content is stored)

Linux (~ and $HOME are equivalent)

$HOME
~

Windows

%USERPROFILE%

Example: finding downloads folder

Linux

$HOME/downloads
~/downloads

windows

%USERPROFILE%\Downloads

PATH Variables

If you go into your terminal and type

echo "Hello World!"

You will notice that works, but you don't have a file called echo.exe (or just echo on macos/linux)

PATH Variable purpose

This is where a special environment variable comes in called your PATH variable. This essentially sets a list of default files/folders that can be called from anywhere. This works differently across OS's so I'll explain it seperately

How PATH works on windows

Windows has a %PATH% variable which is a list of folders, when you type a command it checks if it's an absolute path, then if it's a valid relative path, then it will itterate over every folder in %PATH% and try to find what you're looking for as a relative path

Windows PATH example

Let's say you type

hello-world

Let's say it's not in your CWD and instead is inside %USERPROFILE%/Desktop/hello-world.exe and you have two folders in your %PATH%: %USERPROFILE and %USERPROFILE%/Desktop.

Your terminal will first look at ./hello-world.exe, then at %USERPROFILE%/hello-world.exe then check %USERPROFILE%/Desktop/hello-world.exe at which point it would find it and run it

Reading & updating PATH variable (windows)

You can read your PATH variable by going to a terminal and typing

echo %PATH%

Editing is more complicated, go through the windows GUI as it requires a registry edit that is very volatile at the command line (next slide)

Editing path on windows

How PATH works on *nix (assuming bash)

PATH on *nix has 2 parts, aliases and exported folders. Aliases let you set names as shortcut for binaries (i.e. 'chrome' could be an alias for the chrome browser) or folder exports which work the same ways as windows paths where all binaries inside the folders are accessible.

Where PATH is stored on *nix (assuming bash)

On Linux there will typically be a file at ~/.bashrc where you can make changes, on macos it is typically under ~/.bash_profile

Updating PATH variable (*nix); Adding 'python' binary to PATH

Lets say you have a binary called python3 located at ~/python3 and you want to be able to call it by running python

Linux; Add this line to ~/.bashrc

alias python='~/python3'

MacOS; Add this line to ~/.bash_profile

alias python='~/python3'

Updating PATH variable (*nix); Adding ~/programs directory to PATH

Lets say you have a folder called programs with many binaries located at ~/programs and you want to be able to call the binaries inside it

Linux; Add this line to ~/.bashrc

export PATH="$PATH:~/programs"

MacOS; Add this line to ~/.bash_profile

export PATH="$PATH:~/programs"

Common commands & Concepts

Now lets get into some built in commands and use cases for the terminal!

Getting help

If you're not sure how to use a command you can (usually) use

linux

command -h
command --help

windows

help command

Arguments/flags

Commands will have arguments or flags as they're often called that change how a program operates they are typically in the format

command -f
command --flag
command \F

The first two are the most common, the last form is mostly used in (really) old windows commands. You can also pass arguments (variables or data) with the following syntax

command -f "some text"
command --flag="Some Text"

stdin vs stdout vs stderr

There are 3 'streams' of data that the terminal works with

stdin (standard in): The INput stream that the terminal and commands use

stdout (standard out): The OUTput stream that is what you as a user often read when a command is finished

stderr (standard error): The ERRor stream that looks like stdout to the user, but is specifically for error messages

Piping

You can PIPE the output (stdout) of one command (command1), or some text to the input (stdin) of another command (command2)

command1 | command2

This means command2 will run using the output of command1 as input

Redirecting

You can redirect the output (stdout) of one command (command1), or some text to an output file (test.txt)

command1 > test.txt
command >> test.txt

the single angle bracket means create or replace the file contents with the content being redirected, two angle brackets means create or append the file contents with the content being redirected

Chaining

You can chain together commands to make them run one after another using && (except in powershell)

command1 && command2 && command3

Regex

I am not going to cover regex because it could be it's own presentation. But it's essentially a way of writing rules for finding patterns (i.e. Taking in some text and checking if it's a valid email or a valid phone number)

echo

used to print something, for example printing an environment variable

Linux

echo $HOME

windows

echo %USERPROFILE%

cd

Used to change directoy (update your CWD), for example moving into a folder in cwd called /content

cd content

Those tricks from earlier are all applicable here, so if you want to change your CWD to the directory your current CWD is in you can use

cd ..

mv/move

Used to move files/folders (for example move a folder called /content to your downloads)

linux

mv content ~/downloads/content

Windows

move content %USERPROFILE%\Downloads\content

mkdir

Used to create new folders (same command on *nix and windows)

mkdir folder

touch/echo ' '

Used to create a new blank file (in this example test.txt)

linux

touch test.txt

Windows

echo "" > test.txt

cp

Used to copy a file/folder to another path on linux (for example copying contents to downloads folder)

Linux (copy a file)

cp test.txt ~/downloads/test.txt

Linux (copy a folder)

cp -r /folder ~/downloads/folder

Linux (copy a folder AND it's contents)

cp -r /folder/* ~/downloads/folder

copy/xcopy

Used to copy a file/folder to another path on windows (for example copying contents to downloads folder)

Windows (file)

copy test.txt %USERPROFILE%\Downloads

Windows (folder AND it's contents)

xcopy /E /I folder %USERPROFILE%\Downloads\folder

rm/del

Used to delete files/folders

Linux (deleting a file)

rm test.txt

Linux (deleting a folder)

rm -rf /folder

Windows (del works on files or folders)

del test.txt

cat/type

Used to read the contents of a file

Linux

cat test.txt

Windows

type test.txt

ls/dir

Used to list the contents of a folder (can pass a file path but defaults to CWD)

linux

ls
ls /folder

windows

dir
dir /folder

which/where

Used to find the filepath to the binary being run when you type in a command

linux

which command

windows

where command

zip/(tar or Compress-Archive)

Create a zip/archive file that contains other files/folders (for example putting /folder into a zip/archive file)

linux

zip -r folder.zip folder

windows (powershell)

Compress-archive folder folder.zip

windows (CMD)

tar -cvzf folder.tar folder

grep/findstr

Allows you to find all instances of a string or regex pattern. Typically this is used in conjunction with a pipe for input (for example I can search for lines with 'ezprez' in this presentations source file)

linux

cat example.py | grep ezprez

windows

type example.py | findstr ezprez

Keep in mind this can only be used on text and text-like files, not binaries or binary files. Also you can use this in a loop to search all files in a directory to see which one's contain a certain string or pattern.