What is a Shell?

A Shell is a computer program that allows you to Connect with your computers operating system. This is where you can write code that will directly interact with you computers File System.

Accessing a Shell

In order to code in UNIX or any other Operating Systme (OS), it’s important we know where to access our shell as well as download a shell.

We will look at some shells you can utilize to code in a similar fashion to coding in a UNIX operating system.

  • Accessing Through Your Computer

Most operating systems offer a terminal or console that contains a pre-installed shell. You can search up keywords such as Terminal or Shell to access this.

  • Accessing through File Explorer

You can also use the File Explorer for some operating systems. Right click on a directory such as your documents directory and click Open in Terminal. This will take you into your computers shell.

Installing a Shell

  • Installing the BASH Shell

For most computers, it may be easier to use the Bourne Again Shell(BASH). You can access a tutorial to download this shell [Here]. (https://carpentries.github.io/workshop-template/install_instructions/).

Directory Structure

It’s important to understand all the terminology used when referring to our file system to understand where you are and where commands will take you.

Types of Files

Unix has a wide assortment of files that we will use in our file system.

File Name File Description
Ordinary Files Holds basic file types (csv,txt)
Special Files Files associated with devices such as your printer
Directories Holds Ordinary Files and Special Files in branches beyond the root
Links Shortcuts to a file or directory

Unix Directory Terminology

  • Root

    The root directory is the highest level directory in any Unix System. It is commonly represented by the first / in your file path.

      
root --> /

  • Sub Directories

    As we move into our file system, we will encounter Subdirectories, which can hold files, and other subdirectores.

    Our File System is similar to a plants root system; our Root Directory is our beginning point that connects to our “plant”. As we move through our subdirectories, it’s like were tracing a root down it’s root system.

    With a plant, we would see points where a root breaks off, these points are represented with the / character. They help symbolize What Subdirectory we are in and How Deep we are into our file system.


           -----> Subdirectory ----> file.csv
  root ----|
           |
           -----> Subdirectory

When we want to access a file, we will move through our subdirectories until we reach the directory our file is located in. This path we take is known as the file path.

Example File Path

C:/Subdirectory/file.csv

  • Working Directory

    A working directory is the current field that commands are being ran. Files that are maniuplated or created while your coding will be created in the directory you have set to be your working directory.

Other Types of Directories

There are a wide array of other directories that hold information that is essential for UNIX and CPU functioning

Directories Directory Function
/bin Holds essential system commands
/dev Represents devices attached to the local system
/etc Stores various files for configuration
/home Default locations for file storage
/lib Stores Essential Libraries for bin to run
/media Stores mount for media like flash drives, and USB’s
/mnt Serves as a location for external files and system structures
/proc Allows access to processes and system parameters
/tmp directory for files that are temporary
/usr Stores read only data across the system
/Var Stores variable data that changes as the system is running

We will not look a these extensively in this guide. However, it’s beneficial to know what they are and how to use them.

Syntax

Command Structure

There are four parts to a UNIX command.

  • Prompt

    This is the beginning of your command. it contains information surrounding your System and Current Working Directory.

      
username@ServerCurrentWorkingDirectory$ 'This is the area you will write your commands'

  • Command

    This is where you will write your commands to work with your file system

  • Option

    Allows you to modify the behavior of a command, tbey are extra parameters that you can add

  • Argument

    The argument is where you will be adding the target of your command.

These commands are commonly used in most terminal systems and widely applicable to any console you may be operating on.

File Navigation Commands

Moving through directories requires a strong foundational knowledge of how to do so effectively

  • PWD

    Tells you which directory you are currently working in

  • ls

    Lists all Files and Subdirectories from your Current working directory.

  • cd

    This command has a wide range of uses to help navigate through your file tree.

    Here are some examples.

    
cd / 

'This takes you back to your root directory' 
  
cd.. 
  
'Takes you back to the parent directory you are in (This is the top of the subdirectory)'
  
cd <enter file path>
  
'This will take you down your subdirectory to the next subdirectory or file

File and Directory Manipulation

In the terminal, you are able to move Manipulate Files and Directories to meet your goals.

Directory Manipulation

  • Mkdir

    This command allows you to create a new directory, be careful that your working directory is set to where you want this new branch to be located

     
cd C:/Subdirectory_2
  
         -----> Subdirectory_1 ----> file.csv
         | 
root ----|
         |
         -----> Subdirectory_2

    
mkdir directory_name 
  
         -----> Subdirectory_1 ----> file.csv
         | 
root ----|
         |
         -----> Subdirectory_2 ----> directory_name

here, we created a new directory in Subdirectory_2

You can also make Multiple Directories at once.

           
  
  mkdir dir_1 dir_2 dir_3 
  
           -----> Subdirectory_1 ----> file.csv
           | 
  root ----|    
           |                     |---> dir_1
           -----> Subdirectory_2 |---> dir_2
                                 |---> dir_3

We just made three subdirectories of Subidrectory_2.

We can also remove subirectories with the rmdir command.


cd C:/Subdirectory_2

           -----> Subdirectory_1 ----> file.csv
           | 
  root ----|    
           |                     |---> dir_1
           -----> Subdirectory_2 |---> dir_2
                                 |---> dir_3

rmdir dir_2

           -----> Subdirectory_1 ----> file.csv
           | 
  root ----|    
           |                     |---> dir_1
           -----> Subdirectory_2 |
                                 |---> dir_3

Be careful not to remove a subdirectory that has files or other subdirectories that you need!

File Manipulation

The mv command allows you to move files from place to place.


'make sure your cd is in the directory you want to move your file from'

cd C:/Subdirectory_2

           -----> Subdirectory_1 ----> file.csv
           | 
  root ----|    
           |                     |---> dir_1
           -----> Subdirectory_2 |
                                 |---> dir_3
                                 
mv file.csv /C/Subdirectory_1

                                 
           -----> Subdirectory_1 
           |                     
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3

here, we effectively moved file.csv from Subdirectory_1 to Subdirectory_2.

If we don’t want to move a file but want to make a new file, we can do so using hte Touch command.


cd C:/Subdirectory_1

                                 
           -----> Subdirectory_1 
           |                     
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3
                                 
touch file_2.csv

           -----> Subdirectory_1 --> file_2.csv
           |                     
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3

This created file_2.csv in Subdirectory_1.

If we want a a file in multiple directories, we can copy it using the cp command.

cd C:/Subdirectory_2

           -----> Subdirectory_1 --> file_2.csv
           |                     
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3
                                 
cp C:/Subdirectory2/dir_1/file.csv C:/Subdirectory1

'we first put in the line of code for the file we want to copy, then where we 
want to copy it to.' 
                                 |--> file_2.csv
           -----> Subdirectory_1 |
           |                     |---> file.csv
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3

Similar to our directory removing command, we can remove files uising a rm command.

Once again, be careful not to remove the wrong files and you Cannot undo this.


cd C:/Subdirectory_2


                                 |--> file_2.csv
           -----> Subdirectory_1 |
           |                     |---> file.csv
  root ----|    
           |                     |---> dir_1---> file.csv
           -----> Subdirectory_2 |
                                 |---> dir_3
                                 
rm file.csv


                                 |--> file_2.csv
           -----> Subdirectory_1 |
           |                     |---> file.csv
  root ----|    
           |                     |---> dir_1
           -----> Subdirectory_2 |
                                 |---> dir_3

Summary

UNIX provides a series of functions that allow you to navigate your file directory Understanding how to effectively use these will allow you to access directories and files with ease!

Next Steps

This guide will now focus on how to access and manipulate the contents of files.

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