View source for Linux-New/C2/The-Linux-Environment/English

'''Title of the Script: The Linux Environment.'''

'''Author:''' EduPyramids

'''Keywords:''' Environment variables, local variables, PATH,HOME, profile, history, alias, edupyramids, video tutorial.


{|border=1
|-
|| '''Visual Cue'''
|| '''Narration'''
|-
|| '''Slide 1'''

'''Title Slide'''
|| Welcome to this spoken tutorial on '''The Linux Environment.'''
|-
|| '''Slide 2''' 

'''Learning Objectives'''
|| In this tutorial, we will learn about:
* Linux environment and shell variables
* View and modify environment variables
* Navigate to directories and use '''tilde '''shortcut
* Re-run the commands using history and aliases
* Customize prompts and make rm interactive
|-
|| '''Slide 3'''

'''System Requirements'''
|| To record this tutorial, I am using,
* '''Ubuntu OS version 24 point 04''' 
|-
|| '''Slide 4'''

'''Pre-requisites'''

'''https://EduPyramids.org'''
|| To follow this tutorial,

Learners should have '''Ubuntu version 24 point 04'''

For the prerequisite of Linux tutorials please visit this website.
|-
|| '''Slide 5'''

'''Code Files'''

The following code file is required to practice this tutorial.

'''le-commands.txt'''

This file is provided in the Code Files link of this tutorial page.
|| The following code file is required to practice this tutorial.

This file is provided in the Code Files link of this tutorial page.
|-
|| '''Slide 6 '''

'''Linux Environment'''

'''env-image.png'''
|| * The Linux environment controls how the operating system behaves.
* It determines how commands are processed and actions are interpreted.
* The environment can be customized to suit user preferences.
|-
|| '''Slide 7'''

'''Shell Variables'''

'''image'''
|| The behaviour of the shell is controlled by '''shell variables'''

Shell variables influence how commands execute and display results

There are two main types of''' shell variables:'''
* Environment Variables
* Local Variables
|-
|| '''Slide 8'''

'''Environment Variables'''
|| * Environment variables are available throughout the user’s working environment.
* Inherited by '''subshells''' (for example, when running shell scripts).
* Commonly used to store paths, usernames, language settings, etc.
|-
|| '''Slide 9'''

'''Local Variables'''
|| * Local variables have a limited scope
* They are available only in the current shell session
* They are not available to subshells created by the shell.
|-
|| 
|| This tutorial will mainly focus on environment variables.

We will begin by exploring how to display the values of these variables.
|-
|| Press Ctrl, alt and T keys together. 

Type''' set | more'''

press enter 
|| Let us open the terminal.

To see all the variables available in the current shell, we use the set command. 

Type: '''set space vertical bar space more'''

and press '''Enter'''. 
|-
|| Point to the output.
|| We can see all the current shell variables ,
|-
|| Press Enter and locate the HOME environment.
|| For example, Take a look at the '''HOME''' environment variable and notice the value assigned to it. 
|-
|| Press E'''nter''' 

Press''' q '''
|| Press '''Enter''' to move through the list.

Press '''q''' to come out.
|-
|| Highlight '''set | more'''
|| Here, the output of the '''set '''command is piped to '''more'''.This allows the list of variables to be displayed in a systematic, multi-page format.
|-
|| 
|| To see only the environment variables, we will run the '''e n v''' command. 
|-
|| '''Type '''

'''env | more''' and''' '''press '''Enter''' 
|| Type''' e n v space vertical bar space more '''and press''' Enter'''
|-
|| Highlight '''SHELL=/bin/bash'''
|| 

Notice the '''SHELL''' variable whose value is '''slash bin slash bash. '''
|-
|| Press '''q''' to exit the list
|| Again, you may press '''q''' to come out of the list. 
|-
|| Type '''clear''' and press '''Enter'''.
|| Let’s clear the screen.
|-
|| 
|| Now let us discuss some important '''environment''' '''variables''' in '''linux'''. 
|-
|| 
|| We will use the '''bash''' '''shell''' for all our demonstrations. 
|-
|| 
|| Different shells are customized in slightly different ways. 
|-
|| 

Add $ before name
|| To see a variable’s value, add a '''dollar''' sign before its name.
|-
|| 
|| The first environment variable that we will see is the '''SHELL''' variable. 

It stores the name of the current shell. 
|-
|| Type

'''echo $SHELL '''

Press Enter
|| Type '''echo space dollar SHELL''' in capital and press '''Enter'''. 

The value of the '''SHELL''' variable is as shown .
|-
|| Highlight '''/bin/bash'''
|| Here '''slash bin slash bash''' is the shell where we are currently operating. 
|-
|| 
|| The next variable is '''HOME'''. 
|-
|| 
|| When we log in to Linux, we are placed in a directory named after our username.

This directory is called the '''home directory''', and its path is stored in the '''HOME''' variable.
|-
|| Type at the command prompt 

'''echo $HOME '''and''' '''press '''Enter''' 
|| To see the value, type '''echo space dollar HOME''' in capital and press E'''nter''' 

We see the output as '''slash home slash spoken'''
|-
|| '''The Path Variable''' 
|| The next environment variable is the '''PATH'''. 
|-
|| 
|| The '''PATH''' variable contains the absolute paths of the directories.

The '''shell''' searches them to find executable commands.
|-
|| Type: '''echo $PATH '''

press '''Enter''' 

Highlight the directories.

'''/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/snap/bin ('''This path might differ so while recording please copy the path and paste it here in the script.)
|| Let us now see the value of the '''PATH''' variable.

type '''echo space dollar PATH''' in capital letters and press '''Enter'''.

The output shows the directories present on the system.

This list may vary slightly from one system to another.
|-
|| 
|| It is a list of directories separated by a colon (:).The '''shell''' searches these directories in order to find an executable command.
|-
|| 
|| We can configure the shell to look for commands in our own directory.
|-
|| '''Type PATH=$PATH:/home/spoken''' Highlight '''spoken from above command'''

and press '''Enter'''.
|| Type this command and press '''Enter'''.users can type their home directory's name.

Now, any executable scripts you place in '''slash''' '''home slash spoken '''can be run '''without typing the full path'''.
|-
|| '''Type echo $PATH''' and press '''Enter'''.
|| Now, let’s '''echo''' the value of '''PATH''', to see its current contents.

Type '''echo space dollar PATH''' in capital and press '''Enter'''.
|-
|| Highlight to the added directory
|| Our added directory will also be a part of the '''PATH''' variable. 
|-
|| select and hover over the change in value of path variable 
|| The directory is now available here.

Note that this change is temporary and applies only to this terminal session.
|-
|| '''Type clear'''
|| let us clear the terminal.
|-
|| 
|| Another interesting variable is the '''LOG NAME'''. 

It stores the username of the currently active user. 
|-
|| '''Type echo $LOGNAME'''

press '''Enter'''

Highlight '''spoken'''
|| In order to see the value type '''echo space dollar LOG NAME'''

and press E'''nter'''. Observe that, in the output''' spoken '''is displayed.
|-
|| '''Type PS1="@" '''

and press '''Enter'''.

Highlight the''' @''' sign.
|| Now, let us change the shell prompt.Type the following command and press '''Enter'''.

After pressing Enter, the terminal prompt will change to the at the rate symbol.

This is the primary prompt string represented by the environment variable '''P S 1. '''
|-
|| Press Enter few times to highlight the change displaying @
|| Press '''Enter''' a few times to see the '''at the rate''' prompt.
|-
|| Type bash

and press Enter

Highlight the prompt
|| To get back to the original prompt type

'''bash''' and press''' Enter'''.
|-
|| '''Type echo $PS2 '''and press''' Enter.'''

'''Highlight greater than prompt'''
|| To see the secondary command prompt, type '''echo space dollar P S 2 '''in capital.

and press '''Enter'''. 

Greater than sign is the secondary prompt string represented by the environment variable '''P S 2.''' 

The greater than sign is seen only once and the original prompt appears.
|-
|| 
|| Now let’s try something more interesting.

Let’s display our '''username''' as the''' shell prompt'''.
|-
|| '''Type at the command prompt''' 

'''PS1=$LOGNAME'''

press '''Enter''' 

Highlight the new prompt
|| Type '''P S 1''' in capital '''equals dollar LOGNAME''' and press Enter.

We can see the username '''spoken''' is visible as my prompt.
|-
|| Type: '''PS1="$"'''

and press '''Enter'''
|| To just show a dollar prompt type,

'''P S 1 equals to double quotes dollar double quotes '''and press '''Enter'''.
|-
|| 
|| We have assigned values of several environment variables.
|-
|| Click the + icon on the top left corner.

These changes apply '''only to the current session'''.
|| Open a new tab. 

Observe that these changes apply only to the current session.

That is why a new tab shows the original prompt.

Let us close the new terminal tab.
|-
|| Type '''bash'''

and press '''Enter'''

Highlight the prompt
|| To get back to the original prompt type

'''bash''' and press''' Enter'''.
|-
|| '''Type: echo $PATH'''

Press Enter.
|| For example, we just added our directory to the PATH variable.
|-
|| Press + to open new terminal tab.

type '''echo $PATH '''

and press Enter

Highlight the output
|| Open a new terminal tab and type '''echo DOLLAR PATH''' and press Enter.

The same path variable will not be seen.

let us go back to the previous terminal.
|-
|| Press up direction key 
|| Press the '''Up arrow key''' to see the last command we used.
|-
|| 
|| Keep pressing it to move through earlier commands.
|-
|| Press down direction key 
|| Press the '''Down arrow key''' to move forward again. 
|-
|| '''Type at the command prompt''' 

'''history'''

and press '''Enter'''.
|| However, scrolling through many commands may be clumsy and tedious. 

A better way is to use the '''history '''command.

Type '''history''' and press '''Enter''' to see a list of previously executed commands.
|-
|| '''Type at the command prompt''' 

'''history 10'''

and press '''Enter''' 
|| If you want to see only the last ten commands instead of the full list, 

Type '''history space 10''' and press '''Enter''' 
|-
|| Point to the assigned numbers.
|| Notice, in this list, there is a number assigned to each of the previously executed commands. 
|-
|| '''Type at the command prompt''' 

'''!1348 '''press '''Enter'''.

Highlight the''' output numbers '''
|| To repeat a command, type an exclamation mark followed by its number.

For example '''1348''' in my case would execute '''echo space dollar path.'''

Please note the number may not be the same for you.

Type the number that is seen on your terminal and press Enter to execute the command.
|-
|| Type '''!! '''Press '''Enter'''.
|| To execute the last command, type''' exclamation mark twice''' and press '''Enter'''. 
|-
|| '''Type clear and press Enter.'''
|| let me clear the terminal
|-
|| '''Tilde character Substitution''' type '''cd ~''' press '''Enter.'''
|| Next, we will learn about '''tilde''' '''substitution'''.The tilde''' '''character is a shortcut for the home directory.

type '''c d space''' '''tilde''' press '''Enter.'''
|-
|| Type '''mkdir testtree '''and press '''Enter'''

Type''' cd ~/testtree''', Press '''Enter'''.

Type:''' pwd, '''Press '''Enter'''.
|| Let us create a directory named '''testtree''' in the home directory.

Type: '''m k d i r space test tree '''and press '''Enter'''.

Now type '''cd space tilde slash test tree''', press '''Enter'''.

Type '''p w d''' and Press '''Enter''' to the current directory.
|-
|| (Before the video create such a long directory hierarchy) 
|| The '''alias''' command in Linux is used to create '''shortcuts''' for longer commands.
|-
|| Type

'''mkdir songs'''

and press '''Enter'''

'''cd''' '''songs'''

and press Enter

'''mkdir music'''

and press '''Enter'''

'''cd music'''

and press Enter

Type

'''pwd'''

highlight the long path:

'''/home/spoken/testtree/songs/music'''
|| Let us create a few directories to show a long path in the '''test''' '''tree '''directory.

Type''' m k d i r space songs''' and press '''Enter''' to make the directory.

Type '''c d space songs''' and press '''Enter''' to move the '''songs''' directory.

Now type '''m k d i r space music''' to create the '''music '''directory.

Type''' c d space music''' and press '''Enter''' to move the '''music '''directory.

Let us clear the screen.

Now type '''p w d '''to see the directory path.

This shows that we are now in the music directory.
|-
|| Type''' alias music='cd /home/spoken/testtree/songs/music' '''press '''Enter''' 

type '''cd '''and press '''Enter'''
|| Now type the '''alias''' command and press '''Enter'''.

Let us now go to the home directory. 

Type '''c d''' and press '''Enter.'''
|-
|| Type:''' music''' press '''Enter'''.

Run '''pwd''' to illustrate the effect of the previous command 

|| To switch to the music directory, type '''music''' and press '''Enter'''.

You can see that we are now in the '''music''' directory.
|-
|| '''Type at the command prompt''' 

'''cd -''' 
|| Now, type '''c d space hyphen '''to go back to the previous working directory. 
|-
|| Type''' unalias music'''

press '''enter''' 

Type '''cd '''and press '''Enter'''
|| To remove this alias, type '''unalias space music'''

and press '''Enter'''.Type '''c d '''and press '''Enter''' to go to the home directory.
|-
|| Type''' music''' 

press '''Enter''' 

Highlight the error

|| Now again type '''music''' and press '''Enter.'''

We get an error stating that the command was not found. 
|-
|| Type: '''cd''' '''/home/spoken/testtree/songs/music'''

press Enter
|| Let's go back to the '''music''' directory. 
|-
|| run '''touch test1 test2''' 

run '''ls '''

Highlight '''test1''' and '''test2'''.
|| 

To create '''test 1''' and '''test 2 files''' in the current directory, type '''touch''' '''test 1''' '''test 2''' and Press '''Enter'''.

Command '''touch''' is used to create files in the current directory.

Then run '''l s. '''

This reflects the change on screen.
|-
|| Type''' alias rm="rm -i"''' alias space rm equal to within double quotes rm space hyphen i.

press '''Enter''' 
|| The '''hyphen i''' option of the '''r m''' command makes deletion interactive. So, we can create an alias for the '''r m''' command.

Type '''alias space rm equal to within double quotes rm space hyphen i'''..
|-
|| Type''' rm test1'''

Press '''Enter''' 
|| When we run '''r m test 1''', the file is deleted without showing any output.
|-
|| 
|| The system asks to remove regular empty file '''test 1.'''Type '''y''' and press '''Enter''' to confirm deletion.Now, if we run '''r m''' '''test 1''' and press '''Enter'''.The file is no longer present and as it is already deleted.
|-
|| '''Slide 10'''

'''Summary'''

In this tutorial, we have learnt about:
* Linux environment and shell variables
* View and modify environment variables
* Navigate to directories and use tilde shortcuts
* Re-run commands using history and aliases
* Customize prompts and make rm interactive
|| With this we come to the end of this tutorial.

Let us summarise.
|-
|| '''Slide 11'''

'''Assignment'''

As an assignment
# Type env and list all environment variables.
# Identify the values of HOME, SHELL, LOGNAME, and PATH.
# Temporarily change your PS1 prompt to display your username followed by @Linux:~$.
# Try creating an alias for a long command and use it.
|| As an assignment, please do the following.
|-
|| '''Slide 12'''

'''Thank you'''
|| This Spoken Tutorial is brought to you by EduPyramids Educational Services Private Limited, SINE IIT Bombay.Thank you.
|-
|}