Linux systems - Linux Commands and Shell Scripting

Team Emertxe
Linux Systems
Getting started with setting up an Embedded platform

Linux Systems
Introduction - Let us ponder ...
●
What exactly is an Operating System (OS)?
●
Why do we need OS?
●
How would the OS would look like?
●
Is it possible for a team of us (in the room) to create an
OS of our own?
●
Is it necessary to have an OS running in a Embedded
System?
●
Will the OS ever stop at all?

Linux Systems
Introduction - Operating System
Compiler Assembler Text Editor Database
System and Application Programs
Operating System
Humans
User
Programs
Operating
System
Hardware
HW
Interface/
Privileged
Instr
OS
Interface
Program
Interface

Linux Systems
Introduction - What is Linux?
●
Linux is a free and open source operating system that is
causing a revolution in the computer world
●
Originally created by Linus Torvalds with the assistance of
developers called community
●
This operating system in only a few short years is
beginning to dominate markets worldwide
●
Today right from hand-held devices (ex: Android)
to high end systems (ex: Stock exchange servers)
use Linux

Linux Systems
Introduction - Why use Linux?
●
Free & Open Source –GPL license, no cost
●
Reliability –Build systems with 99.999% upstream
●
Secure –Monolithic kernel offering high security
●
Scalability –From mobile phone to stock market servers
The word 'Free' in Open Source should be interpreted as in
'Freedom' not as 'Free Beer'. This also explains the spirit of
creating Open Source software.

Linux Systems
Introduction - What is Open Source?
Freedom of
software
Freedom of
redistribute
Freedom of
copy
Freedom of
modify
Freedom of
use

Linux Systems
Introduction - Open Source - How it all started?
●
With GNU (GNU is not UNIX)
●
Richard Stallman made the initial announcement in 1983, Free
Software Foundation (FSF) got formed during 1984
●
Volunteer driven GNU started developing multiple projects,
but making it as an operating system was always a challenge
●
During 1991 a Finnish Engineer Linus Torvalds developed core
OS functionality, called it as “Linux Kernel”
●
Linux Kernel got licensed under GPL, which laid strong
platform for the success of Open Source
●
Rest is history!

Linux Systems
Introduction - Open Source - How it evolved?
●
Multiple Linux distributions started emerging around the Kernel
●
Some applications became platform independent
●
Community driven software development started picking up
●
Initially seen as a “geek-phenomenon”, eventually turned out to be
an engineering marvel
●
Centered around Internet
●
Building a business around open source started becoming viable
●
Redhat set the initial trend in the OS business
Customization
Applications
Kernel

Linux Systems
Introduction - Open Source - Where it stands now?
OS Databases Server/Cloud Enterprise
Consumer Education CMS eCommerce

Linux Systems
Introduction - Open Source vs Freeware
OSS Freeware
 Users have the right to access &
modify the source codes
 In case original programmer
disappeared, users & developer
group of the S/W usually keep its
support to the S/W.
 OSS usually has the strong users &
developers group that manage and
maintain the project
 Freeware is usually distributed in a
form of binary at ‘Free of Charge’,
but does not open source codes
itself.
 Developer of freeware could
abandon development at any time
and then final version will be the
last version of the freeware. No
enhancements will be made by
others.
 Possibility of changing its licensing
policy

Linux Systems
Introduction - GPL
●
Basic rights under the GPL – access to source code, right
to make derivative works
●
Reciprocity/Copy-left
●
Purpose is to increase amount of publicly available
software and ensure compatibility
●
Licensees have right to modify, use or distribute
software, and to access the source code

Linux Systems
Introduction - GPL - Issues
●
Linking to GPL programs
●
No explicit patent grant
●
Does no discuss trademark rights
●
Does not discuss duration
●
Silent on sub-licensing
●
Relies exclusively on license law, not contract

Linux Systems
Introduction - Linux Properties
What has made Linux so popular to scale from mobile devices to
powering 90% of world’s super computer? Here are the key
properties of Linux
●
Multitasking
– Ability to handle multiple tasks across single / multiple processors
●
Multi-user
– Have got users with different level of privileges for secured access
●
Protected Memory
– Clear distinction called ‘user-space’ and ‘kernel’ space thereby having protected
memory access. This makes Linux Super secure comparing with other operating systems
●
Hierarchical File System
– Well organized file system that handles various types of files. This also makes handling
various inputs very simple

Linux Systems
Introduction - Linux Components
●
Hardware Controllers: This subsystem is
comprised of all the possible physical
devices in a Linux installation - CPU,
memory hardware, hard disks
●
Linux Kernel: The kernel abstracts and
mediates access to the hardware
resources, including the CPU. A kernel is
the core of the operating system
●
O/S Services: These are services that are
typically considered part of the operating
system (e.g. windowing system, command
shell)
●
User Applications: The set of applications
in use on a particular Linux system (e.g.
web browser)
User
Application
GNU
C
Library
System Call Interface
Kernel
Architecture Dependent
Kernel Code
Hardware Platform
Linux
UserSpaceKernelSpace

Linux Systems
Introduction - Linux Directory Structure
tmp
opt
usr
var
dev
home
media
proc
sbin
boot
etc
lib
mnt
root
bin
/ Essential user command binaries
Static boot-able images
Device files
Host specific configuration
User home directories
Essential shared libraries and kernel modules
Mount point for removable media
Mount point for temporarily mounted file systems
Virtual FS documenting kernel and process status
Root user's home directory
Essential super user command binaries
Add-on application software packages
Temporary files
Multi user utilities and application
Variable files (Logs)

Linux Systems
User Interface - GUI
●
In graphical mode the user will be given a GUI using which he / she will be
able to use the system using mouse
●
Similar to windows based system that exist in other operating systems like
MS Windows & Apple MAC OS

Linux Systems
User Interface - CLI
●
Textual mode used to execute requested commands
Our focus is to be in the CLI mode by executing various commands by invoking shells.
We will also create programs using this environment called ‘Shell scripts’

Linux Systems
User Interface - The Shell - Introduction
●
Shell is an application, works as a command interpreter
●
Gets a command from user, gets it executed from OS
●
Gives a programming environment to write scripts using
interpreted language
●
It has been inherited from UNIX operating system, which was
predecessor to Linux

Linux Systems
User Interface - The Shell - Types
●
Login
– Starts after a successful login
– It is executed under user ID during login process
– It picks up user specific configuration and loads them

Linux Systems
User Interface - The Shell - Types
●
Non Login
– A Non login shell is started by a program without a login
– In this case, the program just passes the name of the shell
executable
– For example, for a Bash shell it will be simply bash
– Following are examples of Non-login shells:
●
sh
●
bash
●
ksh
●
csh

Linux Systems
User Interface - The Shell - Invocation
●
The main task of a shell is providing a user environment
shell
Input
(ls)
List all
the
files
Error
report

Linux Systems
User Interface - The Shell - Bash
●
Bash – The command interpreter
●
GNU Project's shell
●
Bash is the Bourne Again Shell
●
Some features of bash are
– Command line editing
– Unlimited size command history
– Job Control
– Shell Functions and Aliases
– Indexed arrays of unlimited size
– Integer arithmetic in any base from two to sixty-four

Shell Usage and Basic Commands

Linux Systems
Basic Shell Commands – Points to be Noted
●
It is assumed you follow the slides sequence, since some
of the commands explained assumes, you have executed
them before trying the next one
●
After typing the command its expected you press an
enter key

Linux Systems
Basic Shell Commands - pwd
user@user:~] pwd
/home/user
user@user:~]
●
As soon as we open an terminal we are taken to the users
home directory
●
This can be known with the pwd command
●
Basically, the pwd command tells you about current
working directory

Linux Systems
Basic Shell Commands - ls
user@user:~] ls
Desktop Downloads Pictures Templates Videos hello.c
Documents Music Public Test1 bin test2
user@user:~]
●
Well, we come to know where we are, how do we know
what do we have there?
●
The list command ls helps us here. The ls display the
contents of the current directory.
●
Well one question should pop up about the category of
these files?
●
From the above image, can tell which is a directory, file
etc..?

Linux Systems
Basic Shell Commands - man
user@user:~] man ls
●
So how do we come to know about different listing
options?
●
You may use man command, which stands for manual
●
The most useful command which acts as reference
manual if you work in Linux system
●
Almost all the installed applications, libraries and all
would have its own manual entry
●
Even man has its own man page!
user@user:~] man man
●
This helps us to know how read man pages and different
sections in it

Linux Systems
●
Hey, what? It looks too complex!!
●
Well, yes as starter most of the things looks complex,
that too a technical documentation
●
Habit of reading it would certainly make it easy.
MAN(1) ⇐ This is a man page section, There is chance of a command MAN(1)
and libray function have a same name, so section identifies it
NAME
The name of command / function is described here
SYNOPSIS
How to use the command gets described here
DESCRIPTION
Description of the command and function comes here
OTHER SUBSECTION ⇐ Based on the man page different sub section come
below here

Linux Systems
●
So from man page of ls we get the following option
●
Where
user@user:~] ls -F
Desktop/ Downloads/ Pictures/ Templates/ Videos/ hello.c
Documents/ Music/ Public/ Test1/ bin/ test2@
user@user:~]
/ Directory→ Directory
@ Symbolic Link→ Directory
* Executable→ Directory
| Pipe→ Directory
and more

Linux Systems
Basic Shell Commands – Anatomy of a Command
user@user:~] command_name [arguments]
●
A command may have multiple arguments
●
Arguments could be options to the command, file paths or arguments itself
options starts with – which is called as short options which has single letter or –– called as
long options with a word
●
Some of the arguments are optional which is mentioned within [ ]
●
The below example shows the contents of Documents directory with color option enabled
user@user:~] ls -l --color Documents/
●
A command which gets interpreted by shell
●
Could be a super user command which gets executed with sudo
●
The below is an example shows how to install a package in Ubuntu
user@user:~] sudo apt install vim
[arguments]
command_name
user@user:~]
●
Command prompt, which could be customized
●
Default prompt after installation would look like as shown below
user@user:~$

Linux Systems
Basic Shell Commands – Types of commands
●
An executable program like all those files can have in
/usr/bin.
●
A command built into the shell itself. bash provides a
number of commands internally called shell built-ins The
cd command, for example, is a shell built-in
●
A shell function. These are miniature shell scripts
incorporated into the environment.
●
An alias. Commands that you can define yourselves, built
from other commands.

Linux Systems
Basic Shell Commands – Types of commands
●
To know the type of a command, you may try the
following
user@user:~] type <command_name>
user@user:~] type ls
ls is aliased to `ls -v --color=auto'
user@user:~] type pwd
pwd is a shell builtin
user@user:~] type clear
clear is /usr/bin/clear
user@user:~]
●
Few examples

Linux Systems
Basic Shell Commands - cd
user@user:~] ls
Desktop Documents Downloads Music Pictures Public Templates Videos
user@user:~] cd Documents/
user@user:Documents]
●
cd to change directory. A shell built-in command
●
The above example changes the directory to Documents
●
Now how to go back?!
●
We need to understand the concept of the path, which is
explained in the next slide

Linux Systems
Basic Shell Commands - Path
●
Path is the location where a particular file is located in
the directory (tree) structure
●
It starts with the root (‘/’) directory and goes into
appropriate directory
●
The path depends on the reference point from where you
take it up:
– Absolute Path: Specifies the location with reference from
root directory
– Relative Path: Specifies the location with reference to
present working directory (pwd)
●
As the name says relative path will vary depending on your
present working directory

Linux Systems
Basic Shell Commands - Path
tmp
sys
usr
var
dev
home
media
proc
sbin
boot
etc
lib
mnt
root
bin
/
Downloads
Pictures
Templates
Documents
Music
Public
Videos
Desktop
user@user:~] ls
Desktop Documents Downloads Music Pictures
Public Templates Videos
user@user:~]
user

Linux Systems
Basic Shell Commands - Path - Relative
tmp
sys
usr
var
dev
home
media
proc
sbin
boot
etc
lib
mnt
root
bin
/
Downloads
Pictures
Templates
Documents
Music
Public
Videos
Desktop
user
user@user:~] ls
user@user:~] cd Documents/
user@user:Documents]

Linux Systems
Basic Shell Commands - Path - Relative
tmp
sys
usr
var
dev
home
media
proc
sbin
boot
etc
lib
mnt
root
bin
/ user@user:~] ls
user@user:Documents] cd ..
user@user:~]
Downloads
Pictures
Templates
Music
Public
Videos
Desktop
Documents
user

Linux Systems
Basic Shell Commands - Path - Absoulte
tmp
sys
usr
var
dev
home
media
proc
sbin
boot
etc
lib
mnt
root
bin
/
Downloads
Pictures
Templates
Documents
Music
Public
Videos
Desktop
user
user@user:~] ls
user@user:Documents] cd /home/user/
user@user:~]

Linux Systems
Basic Shell Commands - mkdir
user@user:~] ls
user@user:~] mkdir TBD # TBD - ToBeDeleted
user@user:~] ls
Desktop Documents Downloads Music Pictures Public Templates TBD
Videos
user@user:~]
●
mkdir to create directories
●
Creates the directory(ies), if they do not already exists
user@user:~] ls
Videos
user@user:~] mkdir TBD
mkdir: cannot create directory ‘TBD’: File exists
user@user:~]
●
Well, # represents start of comment in shell, anything
written after that would be seen as comment!

Linux Systems
Basic Shell Commands - rmdir
user@user:~] ls
Videos
user@user:~] rmdir TBD
user@user:~] ls
user@user:~]
●
rmdir to remove empty directories
●
Removes the directory(ies), if they are empty
user@user:~] ls
Videos
user@user:~] cd TBD
user@user:TBD] mkdir Test
user@user:TBD] cd ..
user@user:~] rmdir TBD
rmdir: failed to remove 'TBD': Directory not empty
user@user:~]

Linux Systems
Basic Shell Commands - rm
●
The previous slide leads to a question on how to delete a
non empty directory?
●
rm to remove files or directories
●
Removes each specified file. By default, it does not
remove directories.
user@user:~] ls
Videos
user@user:~] ls TBD
Test
user@user:~] rm TBD
rm: cannot remove 'TBD/': Is a directory
user@user:~]
●
Then how??, Well we need to refer the man pages

Linux Systems
●
From the man page or rm you find a option -r which
stands for recursive
user@user:~] rm -r TBD
user@user:~] ls
user@user:~]
●
Note, once deleted, you loose the files permanently!, its
equivalent to Shift + Delete
●
Now what if you delete a file or a folder mistakenly?
Wouldn’t you like that the shell ask you before you
delete? So that you avoid these types of issues!
●
Well will see it in the next slide

Linux Systems
●
The -i option provides interactivity
●
Did you observe from the above screen shot that the shell
prompts before you take any action!, you may say y or n
●
There is always a second chance
●
But what if you forget -i?
user@user:~] ls
Videos
user@user:~] cd TBD
user@user:~] rm -ri TBD
rm: descend into directory 'TBD/'? y
rm: remove directory 'TBD/Test'? y
rm: remove directory 'TBD/'? y
user@user:~]

Linux Systems
Basic Shell Commands - alias
●
The solution the question in the previous slide is alias
●
An builtin bash command, which helps us to name an
operation (command), literally anything
●
Some built aliases are as shown below
user@user:~] alias
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -l'
alias ls='ls --color=auto'
user@user:~]
●
List varies based on your system installation
●
Well how do we create one? How does it solve our issue?

Linux Systems
●
We may create our own alias with required options as
shown below
user@user:~] alias rm=’rm -i’
user@user:~] alias
alias egrep='egrep --color=auto'
alias fgrep='fgrep --color=auto'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -l'
alias ls='ls –color=auto'
alias rm=’rm -i’
user@user:~]
●
Note our alias at the end
●
A new command (operation) named rm is created, when
used henceforth will be rm -i

Linux Systems
●
Lets repeat all the steps again to test our new command
●
Observe that, this time we didn’t provide the -i option!
●
How does it work?, its the because of our alias we
created.
●
The name of new command can be anything, but let it be
meaningful
user@user:~] ls
Videos
user@user:~] cd TBD
user@user:~] rm -r TBD
rm: descend into directory 'TBD/'? y
rm: remove directory 'TBD/Test'? y
rm: remove directory 'TBD/'? y
user@user:~]

Linux Systems
●
The only issue of the new command is that, it is only
available on the terminal it is created??
●
As soon as we close the terminal its all gone!!. So what is
the point. How do we make it permanent??
●
For that we need to about some of the files used by Bash

Linux Systems
Basic Shell Commands – Bash Files
●
Hidden files used by the login as well as non-login shells
●
Found in users home directory
user@user:~] pwd
/home/user
user@user:~] ls -a
. .bash_logout .cache Documents Pictures Templates
.. .bash_profile .config Downloads .profile Videos
.bash_history .bashrc Desktop Music Public .vimrc
user@user:~]
●
These are some configuration files which gets sourced to
bash on every new instance is created

Linux Systems
Basic Shell Commands – Bash Files - .bash_profile
●
Used by the login shell
●
Any action which is to be carried out while logging in
through login shell can be put here
●
Found in the users home directory, if not could be
created

Linux Systems
Basic Shell Commands – Bash Files - .bash_logout
●
Any action which is to be carried out while logging out
through login shell can be put here
●
Found in the users home directory

Linux Systems
Basic Shell Commands – Bash Files - .bashrc
●
Used by the non login shell
●
Any action which is to be carried after you logged into
your machine and open a new terminal window
●
This is executed on every new instance of the new
terminal even if it is in a form of tabs
●
So all those the stuff you would like to get sourced the
bash while starting, then this would be right file
●
By adding the alias in this file would make it persistent
which is raised a question in this slide

Linux Systems
Basic Shell Commands – Bash Files - .bash_history
●
A file which store all the user activity on the command
prompt for future reference.
●
The history command shows the entries of this file

Linux Systems
Basic Shell Commands - touch
●
An command which helps us to update the timestamp of
the existing files
●
If the file argument that does not exist is created empty
user@user:~] cd TBD
user@user:TBD] ls
user@user:TBD] touch file1 file2 file3
user@user:TBD] ls
file1 file2 file3
user@user:TBD]
●
Observe that the directory was empty, using touch command it
created the mentioned files
●
As mentioned it is generally used to update the time stamp, so
you wonder what would be the use of it?
●
Well, they are used by some advanced commands like make

Linux Systems
Basic Shell Commands - touch
●
The scope of this topic is to create some empty files
which will help learning some of the commands we are
going cover next slides
●
But lets see the behavior of the command a bit
user@user:TBD] ls -l
total 0
-rw-rw-r-- 1 user user 0 Nov 30 22:18 file1
user@user:TBD]
●
Note the creation time of all the files
user@user:TBD] touch file1 file2 file3 # 20 Seconds after creation!
user@user:TBD] ls -l
total 0
user@user:TBD]

Linux Systems
Basic Shell Commands - cp
●
cp to copy files and directory
●
Accepts to 2 arguments as the source and destiny
user@user:TBD] cp <source> <destiny>
●
The source and destiny are the path of files to be copied
from and to
user@user:TBD] ls
file1 file2 file3
user@user:TBD] cp file1 file4
user@user:TBD] ls
file1 file2 file3 file4
user@user:TBD] cp file1 ../file5
user@user:TBD] ls ../
Desktop Documents Downloads file5 Music Pictures Public Templates
TBD Videos
user@user:TBD] cp ../file5 .
user@user:TBD] ls
file1 file2 file3 file4 file5
user@user:TBD]

Linux Systems
Basic Shell Commands - cp
●
While copying the directory the -r option has to be used
user@user:TBD] ls
file1 file2 file3 file4 file5 Test
user@user:TBD] cp Test/ TestCopy
cp: -r not specified; omitting directory 'Test/'
user@user:TBD] cp -r Test/ TestCopy
user@user:TBD] ls
file1 file2 file3 file4 file5 Test TestCopy
user@user:TBD] cp file1 file2 file3 Test
user@user:TBD] ls Test/
file1 file2 file3
user@user:TBD]

Linux Systems
Basic Shell Commands - mv
●
mv to move of rename files and directories
●
Accepts to 2 arguments as the source and destiny
user@user:TBD] mv <source> <destiny>
●
The source and destiny are the path of files to be moved
or renamed from and to
Desktop Documents Downloads file5 Music Pictures Public Templates
TBD Videos
user@user:TBD] mv ../file5 TestCopy
user@user:TBD] ls TestCopy
file5
Videos
user@user:TBD]
●
Note the above context, the file gets moved

Linux Systems
Basic Shell Commands - mv
user@user:TBD] ls
file1 file2 file3 file4 file5 Test TestCopy
user@user:TBD] mv file1 file1.txt
user@user:TBD] ls
file1.txt file2 file3 file4 file5 Test TestCopy
user@user:TBD]
●
In this context, the file gets renamed

Linux Systems
Visual Editor - vi
●
Screen-oriented text editor originally created for the
Unix operating system
●
The name vi is derived from the shortest unambiguous
abbreviation for the ex command visual
●
Improved version is called as vim
●
To open a file
user@user:TBD] vi <file_name>
user@user:TBD] vim <file_name>
or

Linux Systems
Visual Editor - vim
Mode Functions Key
Escape Search
File Edit
Esc
Edit Insert
Replace
i / I
r / R
Visual Selection v / V
Command Line Commands :
●
vi opens a file in command mode to start mode.
●
The power of vi comes from the following modes
●
To get a basic grip on vi you may type vimtutor on the
terminal. Just read and follow the instructions
user@user:TBD] vimtutor

Linux Systems
Visual Editor – vim - Information
user@user:TBD] ls
user@user:TBD] vi file.txt
█
~
~
~
~
~
~
~
~
~
"file.txt" [New File] 0,0-1 All
filename,
mode,
previous action
command prompt
line, cursor view %file
command
information

Linux Systems
Visual Editor – vim - Modes
This is the mode where, you would be entering the text. Most of the file
Commands will not work here!. Press i anytime while in ESC mode
~
-- INSERT -- 2,63 All
Insert Mode. Press i
This mode is default as soon as you open a file. You may press ESC key any
time to enter this mode
~
2,23 All
Escape Mode. Press ESC
The existing text will be over written or replaced with new one. You may
press R anytime to get into this mode while in ESC mode
~
-- REPLACE -- 2,55 All
Replace Mode. Press ESC Press R

Linux Systems
This mode helps us to select a part of the content.
You may press ESC and v to enter into this mode and your arrow keys to select
the text you want. After that you may use any of the file edit command and
perform the required opertion. Observe the selection made above!!
~
-- VISUAL -- 2 3,18 All
Visual Mode. Press ESC Press v
This mode helps us to select a part of the content.
You may press ESC and CTRL v to enter into this mode and your arrow keys to
select the block you want. After that you may use any of the file edit
command and perform the required opertion. Observe the selection made!!
~
-- VISUAL BLOCK -- 4x20 4,42 All
Visual Block Mode. Press ESC Press Ctrl v

Linux Systems
Press ESC and : brings us in command mode.
You may use the command required and press ENTER
~
~
:<Type your command here>
Command Line Mode. Press ESC Press :

Linux Systems
Visual Editor – vi – Insert
~
"test.txt" [New File] 0,0-1 All
Press i
user@user:TBD] vi test.txt
~
~
Start typing something
Hey all!, let do some vimming :)
~
Press ESC

Linux Systems
Visual Editor – vi – Insert and Undo
~
"file.txt" 1L, 67C 1,32 All
Press i and start typing something
Hey all!, let do some vimming :THE TEXT GETS INSERTED HERE)
~
Hey all!, let do some vimming :THE TEXT GETS INSERTED HERE)
~
^[ 1,59 All
Press u to Undo
~
1 change; before #4 1 seconds ago 1,32 All
Press ESC

Linux Systems
Visual Editor – vi – Insert
Press I and observe the cursor and start typing
~
THE TEXT GETS INSERTED HEREHey all!, let do some vimming :)
~
^[ 1,28 All
Press ESC
THE TEXT GETS INSERTED HEREHey all!, let do some vimming :)
~
1,27 All
Press u to Undo
~

Linux Systems
Visual Editor – vi – Write and Quit
~
~
~
:w
To save. Press w and ENTER
~
~
~
:"test.txt" 1L, 57C [w] 1,56 All
~
~
~
:q
To quit. Press q and ENTER

Linux Systems
user@user:TBD] ls
user@user:TBD] ls
file1.txt file2 file3 file4 file5 Test TestCopy test.txt
user@user:TBD]
●
Just to understand this better, lets learn the cat
command before we proceed further

Linux Systems
vi - Basic Shell Commands - cat
user@user:TBD] ls
user@user:TBD] ls
file1.txt file2 file3 file4 file5 Test TestCopy test.txt
user@user:TBD] cat test.txt
user@user:TBD]
●
Displays the contents of the file on the screen
●
cat has many advanced functionalities which will be
covered later as required
●
cat to concatenate files and print on standard output

Linux Systems
~
~
~
:wq
To save and quit. Press wq and ENTER
Added this line too!! which will be missing!
~
~
:q!
To quit without saving. Press q! and ENTER

Linux Systems
Visual Editor – vi – Append
~
Press a and start typing something
HTHE TEXT GETS INSERTED HEREey all!, let do some vimming :)
~
HTHE TEXT GETS INSERTED HEREr all!, let do some vimming :)
~
^[ 1,1 All
~
Press ESC
Press u to Undo

Linux Systems
Visual Editor – vi – Append
Press A and start typing something
~
Hey all!, let do some vimming :)THE TEXT GETS INSERTED HERE
~
^[ 1,1 All
~
Press ESC
Press u to Undo
Hey all!, let do some vimming :)THE TEXT GETS INSERTED HERE
~
^[ 1,28 All

Linux Systems
Visual Editor – vi – Yank (Copy) and Paste
~
1 change; before #4 1 seconds ago y 1,1 All
Press ESC and yy and start typing something Press p
~
~
●
You may copy multiple lines and paste times using the
following syntax
– [n]yy – Copy n line(s) Say n = 10, 10yy copies 10 lines→ Directory
– [n]p – Paste copied line(s) n time Say n = 10, 10p→ Directory
pastes the copied line(s) 10 times
●
Note, this rule applies to almost all the commands

Linux Systems
Visual Editor – vi – Open
~
~
Press o
~
Press u to UndoPress ESC
~
~

Linux Systems
Visual Editor – vi – Open
~
~
Press O
~
Press 2u to UndoPress ESC
~
~
~
2 fewer lines; #4 1 seconds ago 2,1 All

Linux Systems
Visual Editor – vi – Increment
1 line Hey all!, let do some vimming :)
~
1 change; before #4 1 seconds ago y 1,1 All
Press ESC and yy and start typing something Press p
~
~
Press CRTL a and observe the 2nd
line
Press yyp
~
~

Linux Systems
Visual Editor – vi – Go
~
Press CRTL a and observe the 3rd
line
~
Press gg and observe the cursor position
~

Linux Systems
Visual Editor – vi – Go
●
The most useful shortcut to navigate between different
lines
– [n]gg – Go to nth line Say n = 10, 10gg takes you to 10→ Directory
line
– gg take you the first line of the file
– G take you the last line of the file

Linux Systems
Visual Editor – vi – Delete
~
Press 2dd and observe
~
~
~
●
You may delete multiple lines from the current cursor
position
– [n]dd – Delete n line(s) Say n = 10, 10dd delete 10 lines→ Directory
– D the current line from the cursor position

Linux Systems
Visual Editor – vi – Decrement
Press 2 CTRL x and observe
~
~
~
●
You may increment and decrement n times
– [n]CTRL x – Increments the first integer match from the
cursor position Say n = 10 and number is 13,→ Directory
10 CTRL x decrements the number by 10,
resulting to number 3
– The increments works the same way

Linux Systems
Visual Editor – vi – Navigation - Forward
Press w and observe cursor1 line Hey all!, let do some vimming :)
~
~
~
1,1 All
~
~
~
1,8 All
Press w and observe cursor
~
~
~
1,18 All
Press 3w and observe cursor
●
[n]w – Move forward n words Say n = 10w – move 10 words→ Directory
ahead

Linux Systems
Visual Editor – vi – Navigation - Backward
Press b and observe cursor1 line Hey all!, let do some vimming :)
~
~
~
1,18 All
~
~
~
1,15 All
Press b and observe cursor
~
~
~
1,18 All
Press 2b and observe cursor
●
[n]b – Move backward n words Say n = 10b – move 10→ Directory
words behind

Linux Systems
Visual Editor – vi – Change Word
~
~
~
1,18 All
Press cw and observe
●
[n]cw – Change n words Say n = 10cw – change 10 words→ Directory
from the current cursor position
1 line all!, let do some vimming :)
~
~
~
You may insert the new words

Linux Systems
Visual Editor – vi – Delete Word
~
~
~
1 change; before #16 1,18 All
Press u to Undo
●
[n]dw – Delete n words Say n = 10dw – delete 10 words→ Directory
from the current cursor position
1 line all!, let do some vimming :)
~
~
~
1,8 All
Press dw and observe

Linux Systems
Visual Editor – vi – Settings
~
~
~
:
Press : to enter Command Line
Mode
~
~
~
:set hls
Type set hls and ENTER
to enable search highlights
●
:set hls – Enable highlight search
●
:set nohls – Disable highlight search
●
:set nu – Enable line numbers
●
:set nonu – Disable line numbers

Linux Systems
Visual Editor – vi – Search - Forward
●
[n]n – Forward search n words Say n = 10n – Searches the→ Directory
10 words from the current position forward
~
~
~
/e 1,6 All
Press / and type search pattern
and ENTER
~
~
~
/e 1,9 All
Press n

Linux Systems
Visual Editor – vi – Search - Backward
●
[n]n – Reverse search n words Say n = 10n – Searches the→ Directory
10 words from the current position backwards
~
~
~
/e 1,9 All
Press N
~
~
~
search hit TOP, continuing at BOTTOM All
Press 3N and observe the
cursor position
~
~
~
:set nohls
Type :set nohls and ENTER
to disable search highlights

Linux Systems
Visual Editor – vi – Settings
~
~
~
:
Mode
~
~
~
:set nohls
Type set hls and ENTER
to enable search highlights
1 1 line Hey all!, let do some vimming :)
~
~
~
:set nu
Type set nu and ENTER
to enable line numbers

Linux Systems
Visual Editor – vi – Substitute
~
~
~
:set nu
Type yy and 2p
~
:set nu
Mode
~
:
Mode
~
:%s/vimming/VIMMING/g
Type
%s/vimming/VIMMING/g

Linux Systems
Visual Editor – vi – Substitute
1 1 line Hey all!, let do some VIMMING :)
~
3 substitutions on 3 lines
Substitutes the pattern globally
3 1 line HEY all!, let do some VIMMING :)
~
:3s/Hey/HEY/g
Substitutes the pattern on the
Specified line(s)
1 1 linEE Hey all!, let do some VIMMING :)
2 1 linEE Hey all!, let do some VIMMING :)
3 1 linEE HEY all!, let do some VIMMING :)
~
:%s/e/EE/
Substitutes the first occurrence
of pattern globally
●
Interesting pattern substitutions possible if have knowledge on
Regular Expressions

Linux Systems
Visual Editor – vi – Edit and Read
●
Edit
– :e filename - open another file without closing the
current
– To switch between these files use CTRL 6. Make sure
the file is save
– You will not be able to undo after the switch
●
Read
– :r filename - reads file named filename at the current
cursor position

Linux Systems
Shell Scripting - Programming Languages
●
There are various types of programming languages,
compared on various parameters
●
From Embedded system engineer’s view it should be seen
how close or how much away from the hardware the
language is
●
Based on that view programming languages can be
categorized into three areas:
– Assembly language (ex: 8051)
– Middle level language (ex: C)
– High level / Scripting language (ex: Shell)

Linux Systems
Shell Scripting - Programming Languages
●
Each programming language offers some benefits with
some shortcomings
●
Depending on the need of the situation appropriate
language needs to be chosen
●
This make language selection is a key criteria when it
comes to building real time products!

Linux Systems
Shell Scripting – Prog... Lang... – A Comparison
Language
parameter
Assembly C Shell
Speed High Medium Medium
Portability Low Medium High
Maintainability Low Medium High
Size Low Medium Low
Easy to learn Low Medium High
Shell or any scripting language is also called as ‘interpreted’ language as it doesn’t
go through compilation phase. This is to keep the language simple as the purpose is
different than other languages.

Linux Systems
Shell Scripting – What is a Script?
●
Any collection of shell commands can be stored in a file,
which is then called as shell script
●
Programming the scripts is called shell scripting
●
Scripts have variables and flow control statements like
other programming languages
●
Shell script are interpreted, not compiled
●
The shell reads commands from the script line by line and
searches for those commands on the system

Linux Systems
Shell Scripting - Script – Where to use?
●
System Administration
– Automate tasks
– Repeated tasks
●
Development
– Allows testing a limited sub-set
– Testing tools
●
Daily usage
– Simple scripts
– Reminders, e-mails etc…

Linux Systems
Shell Scripting - Script – Example
1 #!/bin/bash
2 echo "Hello World" # Print Hello World on standard output
~
~
:wq
user@user:Classwork] vi hello.sh
user@user:~] cd # Move to home directory
user@user:~] mkdir -p ECEP/LinuxSystems/Classwork
user@user:~] cd ECEP/LinuxSystems/Classwork
user@user:Classwork]
user@user:Classwork] bash hello.sh
Hello World
user@user:Classwork] ls -l
-rw-rw-r-- 1 adil adil 31 Dec 2 21:44 hello.sh
user@user:Classwork] chmod +x hello.sh
user@user:Classwork] ls -l
-rwxrwxr-x 1 adil adil 31 Dec 2 21:44 hello.sh
user@user:Classwork] ./hello.sh
Hello World

Linux Systems
Shell Scripting - Script – echo
user@user:Classwork] echo Hello World
Hello World
●
echo displays a line of text
●
Helps use to print on screen with required formatting
●
Used in scripts to print normal messages and the value of
variable, which will be seeing shortly
●
Some examples are as shown below
user@user:Classwork] echo HellonWorld # To print on 2 seperate line
HellonWorld
user@user:Classwork] echo -e “HellonWorld” # To print on 2 seperate line
Hello
World
user@user:Classwork] echo -e “HellotWorld” # To words with tab
Hello World
user@user:Classwork] echo -e “HellorWorld” # To overwrite previous print
World

Linux Systems
Shell Scripting - Special Characters
user@user:Classwork] echo ~ # Expands to users home directory path
/home/user
●
Characters which has special meaning
●
Used in many advanced functionalities
●
Lets understand some of the most important ones
user@user:Classwork] firefox
⇐ Observe here, the shell would be held by the application you invoked!!
~ → Directory The current user's home directory
& Open applications or commands→ Directory in the background
user@user:Classwork] firefox & # firefox is opened in background
[1] 7746
user@user:Classwork] # You may use the command prompt

Linux Systems
user@user:Classwork] mkdir TBD
user@user:TBD] cd TBD
user@user:TBD] touch file_{1..5}.txt # Create 5 files from 1 to 5
user@user:TBD] touch file_{6..10}.c
user@user:TBD] touch file_{1..5}.sh
user@user:TBD] ls
file_10.c file_13.sh file_1.txt file_4.txt file_7.c
file_11.sh file_14.sh file_2.txt file_5.txt file_8.c
file_12.sh file_15.sh file_3.txt file_6.c file_9.c
user@user:TBD] ls *.txt
file_1.txt file_2.txt file_3.txt file_4.txt file_5.txt
user@user:TBD] ls *1*
file_10.c file_12.sh file_14.sh file_1.txt
file_11.sh file_13.sh file_15.sh
user@user:TBD]
* → wildcard, matching zero or more characters (e.g. : ls doc_*)

Linux Systems
user@user:TBD] ls
file_10.c file_13.sh file_1.txt file_4.txt file_7.c
file_11.sh file_14.sh file_2.txt file_5.txt file_8.c
file_12.sh file_15.sh file_3.txt file_6.c file_9.c
user@user:TBD] ls file_?.c
file_6.c file_7.c file_8.c file_9.c
user@user:TBD] ls file_??.c
file_10.c
user@user:TBD] ls file_??.*
file_10.c file_11.sh file_12.sh file_13.sh file_14.sh file_15.sh
user@user:TBD]
? → wildcard, matching exactly one character (e.g.: ls doc_?)

Linux Systems
user@user:TBD] echo $ # Note, A $ with any non space character will be seen
as a variable. Will see this in next few slides
$
user@user:TBD] echo $0 # Expands to name of the shell or shell script
/bin/bash
user@user:TBD] echo $$ # Expands to this shell process id
2668
user@user:TBD] echo $? # Expands to the status of the previous command
0
user@user:TBD]
$ → used to access a variable (e.g. : $HOME), used with echo command
●
There 2 more which makes sense in a script will see them
shortly
– $@ → Directory Value of all arguments passed
– $# → Directory No of arguments passed to shell script

Linux Systems
Shell Scripting - Variables
●
Variables are a way of storing information temporarily
●
A couple of conversions we need to follow
– Variables usually appear in uppercase
– There should not be a white space between the variable
name and the equal sign
user@user:TBD] X=10
user@user:TBD] echo $X # Any non space charater adjacent to $ is a variable
10
user@user:TBD] NAME=”EMERTXE”
user@user:TBD] echo $NAME
EMERTXE
user@user:TBD] echo $DUMMY # The DUMMY variable is not set. Hence no print
user@user:TBD]

Linux Systems
Shell Scripting - White-space & Line-breaks
●
Bash shell scripts are very sensitive to white-space & line-
breaks
●
Because the “keywords” of this programming language are
actually commands evaluated by the shell
●
Need to separate arguments with white spaces
●
Likewise a line-break in the middle of a command will mislead
the shell into thinking the command is incomplete.
user@user:TBD] TEST = 10 # Not allowed
TEST: command not found
user@user:TBD] TEST1=10; TEST2=20 # Allowed
user@user:TBD] echo $TEST1 $TEST2
10 20
user@user:TBD]

Linux Systems
Shell Scripting - The Shell Env Variables
●
Login-shell's responsibility is to set the non-login shell and
it will set the environment variables
●
Environment variables are set for every shell and
generally at login time
●
Environmental variables are set by the system.
●
env - lists shell environment variable/value pairs

Linux Systems
Shell Scripting - The Shell Env Variables
user@user:TBD] echo $HOME # The current user's home directory
/home/user
user@user:TBD] echo $SHELL # Shell that will be interpreting user commands
/bin/bash
user@user:TBD] echo $USER # The current logged in user
user
user@user:TBD] echo $PWD # The previous working directory
/home/user/ECEP/LinuxSystems/Classwork/TBD
user@user:TBD] echo $OLDPWD # The previous working directory
/home/user
user@user:TBD] echo $PATH # System will check when looking for commands here
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/
local/games:/snap/bin:
user@user:TBD] echo $HOSTNAME # The hostname of the computer
emertxe
user@user:TBD] echo $TERM # Type of terminal to emulate when running the shell
xterm-256color
user@user:TBD] echo $PS1
[e]0;u@h: wa]${debian_chroot:+($debian_chroot)}[033[01;32m]u@h[
033[00m]:[033[01;34m]W[033[00m]]
user@user:TBD]

Linux Systems
Shell Scripting - Quotes
●
Using double quotes to show a string of characters will
allow any variables in the quotes to be resolved
user@user:TBD] VAR=10
user@user:TBD] echo $VAR
10
user@user:TBD] echo “The value is $VAR”
The value is 10
user@user:TBD]
●
Using single quotes causes the variable name to be used
literally, and no substitution will take place
user@user:TBD] VAR=10
user@user:TBD] echo $VAR
10
user@user:TBD] echo ‘The value is $VAR’
The value is $VAR
user@user:TBD]

Linux Systems
Shell Scripting - Expressions
●
expr Evaluates simple math on the command line
calculator
●
bc An arbitrary precision calculator language
user@user:TBD] expr 10 + 20
30
user@user:TBD] expr 10 * 20
expr: syntax error
user@user:TBD] expr 10 * 20 # * acts a wildcard, so need to escape it
200
user@user:TBD]
user@user:TBD] bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundati
on, Inc. This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'./
10 * 20
200
10 + 34 * 23
792
quit
user@user:TBD]

Linux Systems
Shell Scripting – Expressions - Script
user@user:TBD] cd ../PPT-Examples
user@user:PPT-Examples]
1 #!/bin/bash
2
3 NUM1=5
4 NUM2=3
5
6 ADD=$((${NUM1} + ${NUM2}))
7 SUB=$((${NUM1} - ${NUM2}))
8 MUL=$((${NUM1} * ${NUM2}))
9 DIV=$((${NUM1} / ${NUM2}))
10 MOD=$((${NUM1} % ${NUM2}))
11
12 echo -e "Addition of two numbers istt: ${ADD}"
13 echo -e "Substraction of two numbers istt: ${SUB}"
14 echo -e "Multiplication of two numbers ist: ${MUL}"
15 echo -e "Division of two numbers istt: ${DIV}"
16 echo -e "Modulum of two numbers istt: ${MOD}"
~
"1_expression.sh" 16L, 418C 0,0-1 All
user@user:PPT-Examples] vi 1_expression.sh

Linux Systems
Shell Scripting – Expressions - Script
user@user:PPT-Examples] chmod +x 1_expression.sh
user@user:PPT-Examples] ./1_expression.sh
Addition of two numbers is : 8
Substraction of two numbers is : 2
Multiplication of two numbers is : 15
Division of two numbers is : 1
Modulum of two numbers is : 2

Linux Systems
Shell Scripting - Conditions – if else
●
The if statement chooses between alternatives each of
which may have a complex test
●
The simplest form is the if-then statement
if [ condition ]
then
expression
else
expression
fi
Syntax

Linux Systems
Shell Scripting - Conditions – if else
1 #!/bin/bash
2
3 NUM1=5
4 NUM2=3
5
6 if [ ${NUM1} -gt ${NUM2} ]
7 then
8 echo "NUM1 is greater than NUM2"
9 else
11 fi
~
"2_if_then.sh" 11L, 139C 0,0-1 All
user@user:PPT-Examples] vi 2_if_then.sh
user@user:PPT-Examples] chmod +x 2_if_then.sh
user@user:PPT-Examples] ./2_if_then.sh
NUM1 is greater than NUM2

Linux Systems
Shell Scripting - Conditions – if else if
●
Multiple if blocks can be strung together to make an
elaborate set of conditional responses
if [ condition_a ]
then
condition_a is true
elif [ condition_b ]
then
condition_b is true
else
both false
fi
Syntax

Linux Systems
Shell Scripting - Conditions – if else if
1 #!/bin/bash
2
3 NUM1=5
4 NUM2=3
5
6 if [ ${NUM1} -eq ${NUM2} ]
7 then
8 echo "NUM1 is equal to NUM2"
9 elif [ ${NUM1} -gt ${NUM2} ]
10 then
12 else
13 echo "NUM1 is less than NUM2"
11 fi
~
"3_if_elif.sh" 14L, 200C 0,0-1 All
user@user:PPT-Examples] vi 3_if_elif.sh
user@user:PPT-Examples] chmod +x 3_if_elif.sh
user@user:PPT-Examples] ./3_if_elif.sh
NUM1 is less than NUM2

Linux Systems
Shell Scripting - Conditions – case
●
The case statement compares the value of
the variable ($var in this case) to one or
more values
●
Once a match is found, the associated
commands are executed and the case
statement is terminated
●
Used to execute statements based on
specific values
●
Often used in place of an if statement if
there are a large number of conditions.
●
Each set of statements must be ended by a
pair of semicolon
●
*) is used for not matched with list of
values
case ${VAR} in
value_1)
commands;
;;
value_2)
commands;
;;
*)
commands;
;;
esac
Syntax

Linux Systems
1 #!/bin/bash
2
3 echo “Enter a number:”
4 read NUM
5
6 case ${NUM} in
7 1)
8 echo "You entered One"
9 ;;
10 2) echo "You entered Two"
11 ;;
12 *) echo "Obey my orders please" ;;
13 esac
~
~
"4_case_statements.sh" 13L, 187C 0,0-1 All
user@user:PPT-Examples] vi 4_case_statments.sh

Linux Systems
user@user:PPT-Examples] chmod +x 4_case_statements.sh
user@user:PPT-Examples] ./4_case_statements.sh
“Enter a number < 3:”
2
You entered Two
user@user:PPT-Examples] ./4_case_statements.sh
“Enter a number < 3:”
5
Obey my orders please

Linux Systems
Shell Scripting – Numeric Test Operators
Operator Functions
-eq Compare if two numbers are equal
-ge Compare if one number is greater than or equal to num
-le Compare if one number is less than or equal to a num
-ne Compare if two numbers are not equal
-lt Compare if one number is less than another number
-gt Compare if one number is greater than another number

Linux Systems
Shell Scripting - String Tests
●
String comparison, Numeric comparison, File operators
and logical operators
●
Comparison operations are provided below
Operator Functions
= Compare if two strings are equal
!= Compare if two strings are not equal
-n Evaluate if string length is greater than zero
-z Evaluate if string length is equal to zero

Linux Systems
1 #!/bin/bash
2
3 echo “Enter the first string”
4 read STR1
5 echo “Enter the second string”
6 read STR2
7
8 if [ -z ${STR1} ]; then
9 echo "First string is empty"
10 else
11 echo "First string is not empty"
12 fi
13 if [ -n ${STR2} ]; then
14 echo "Second string is not empty"
15 else
16 echo "Second string is empty"
17 fi
18 if [ ${STR1} = ${STR2} ]; then
19 echo "Both strings are equal"
20 else
21 echo "Both strings are not equal"
22 fi
~
"5_string_test.sh" 22L, 405C 0,0-1 All
user@user:PPT-Examples] vi 5_string_test.sh

Linux Systems
user@user:PPT-Examples] chmod +x 5_string_test.sh
user@user:PPT-Examples] ./5_string_test.sh
“Enter the first string”
Hello
“Enter the second string”
World
First string is not empty
Second string is not empty
Both strings are not equal
user@user:PPT-Examples] ./5_string_test.sh
“Enter the first string”
Hello
“Enter the second string”
Hello
First string is not empty
Second string is not empty
Both strings are equal

Linux Systems
Shell Scripting – Logical Operators
Operator Functions
! Compare if two strings are equal
-a Logically AND two logical expression
-o Logically OR two logical expressions
1 #!/bin/bash
2
3 echo “Enter the first number A” ; read A
4 echo “Enter the second number B” ; read B
5 echo “Enter the third number C” ; read C
6
7 if [ ${A} -gt ${B} -a ${A} -gt ${C} ]; then
8 echo "A is the greatest of all"
9 elif [ ${B} -gt ${A} -a ${B} -gt ${C} ]; then
10 echo "B is the greatest of all"
14 elif [ ${C} -gt ${A} -a ${C} -gt ${B} ]; then
15 echo "C is the greatest of all"
16 else
17 echo "Invalid Input"
18 fi
"6_logical_operators.sh" 18L, 426C 0,0-1 All
user@user:PPT-Examples] vi 6_logical_operator.sh

Linux Systems
Shell Scripting - Logical Operator
user@user:PPT-Examples] chmod +x 6_logical_operator.sh
user@user:PPT-Examples] ./6_logical_operator.sh
“Enter the first number A”
10
“Enter the second number B ”
2
“Enter the third number C ”
3
A is the greatest of all
user@user:PPT-Examples] ./6_logical_operator.sh
“Enter the first number A”
3
“Enter the second number B ”
10
“Enter the third number C ”
2
B is the greatest of all

File Specific Commands
and Operators

Linux Systems
File Specific Cmds & Opers - more
●
more helps us to view a file content page wise
user@user:PPT-Examples] more 2_if_then.sh # Use q to quit
#!/bin/bash
NUM1=15
NUM2=6
if [ ${NUM1} -gt ${NUM2} ]
then
echo "NUM1 is greater than NUM2"
else
fi
●
Note, if the file size if greater than the window size you
would have page view
●
You may try the below example
user@user:PPT-Examples] sudo more /var/log/syslog

Linux Systems
File Specific Cmds & Opers - less
●
less similar to more with many features
user@user:PPT-Examples] less 2_if_then.sh # Use q to quit
●
Note, if the file size if greater than the window size you
would have page view
●
You may try the below example
user@user:PPT-Examples] sudo less /var/log/syslog
#!/bin/bash
NUM1=15
NUM2=6
if [ ${NUM1} -gt ${NUM2} ]
then
else
fi
2_if_then.sh (END)

Linux Systems
File Specific Cmds & Opers - | (pipe)
●
A pipe is a form of redirection that is used in Linux
operating systems to send the output of one program to
another program for further processing.
●
A pipe is designated in commands by the vertical bar
character
user@user:PPT-Examples] ls
10_cmd_line_args.sh 4_string_test.sh 8_while_loop.sh
1_expressions.sh 5_logical_operators.sh 9_arrays.sh
2_if_then.sh 6_case_statements.sh
3_if_elif.sh 7_for_loop.sh
user@user:PPT-Examples] ls | wc # Gives the word count info from ls output
10 10 166
●
It is a very useful operator. Well see some more usage in
later slide

Linux Systems
File Specific Cmds & Opers - head
●
head helps us to output the first part of files
user@user:PPT-Examples] head -5 1_expressions.sh # Print first 5 lines
#!/bin/bash
NUM1=5
NUM2=3
user@user:PPT-Examples] ls -1v | head -5 # Print first 5 lines for ls output
1_expressions.sh
2_if_then.sh
3_if_elif.sh
4_string_test.sh
5_logical_operators.sh

Linux Systems
File Specific Cmds & Opers - tail
●
tail helps us to output the last part of files
user@user:PPT-Examples] tail -5 1_expressions.sh # Print last 5 lines
echo -e "Addition of two numbers istt: ${ADD}"
echo -e "Substraction of two numbers istt: ${SUB}"
echo -e "Multiplication of two numbers ist: ${MUL}"
echo -e "Division of two numbers istt: ${DIV}"
echo -e "Modulum of two numbers istt: ${MOD}"
user@user:PPT-Examples] ls -1v | tail -5 # Print first 5 lines for ls output
7_for_loop.sh
7_while_loop.sh
6_case_statements.sh
9_arrays.sh
10_cmd_line_args.sh

Linux Systems
File Specific Cmds & Opers - Redirection
●
Operators used to redirect data
– From a file to a command – Input Redirection → Directory <
– To a file from the command – Output Redirection → Directory >
●
We may control the data stream which passed to the file
– 1> from stdout to file→ Directory
– 2> from stdin file→ Directory
●
Data can be appended to an existing file
– >>
●
The functions discussed here basic
●
Many advanced functions are available if required

Linux Systems
2_if_then.sh 6_case_statements.sh
3_if_elif.sh 7_for_loop.shh
user@user:PPT-Examples] echo Hello > test.txt
2_if_then.sh 6_case_statements.sh test.txt
user@user:PPT-Examples] cat text.txt
Hello
user@user:PPT-Examples] echo World > test.txt # Overwrites the files
World
user@user:PPT-Examples] echo Hello >> test.txt
World
Hello

Linux Systems
2_if_then.sh 6_case_statements.sh test.txt
user@user:PPT-Examples] ls 9_arrays.sh 1234 > test.txt
ls: cannot access '1234': No such file or directory
9_arrays.sh
user@user:PPT-Examples] ls 9_arrays.sh 1234 2> test.txt
9_arrays.sh
ls: cannot access '1234': No such file or directory
user@user:PPT-Examples] echo 1 + 2 > text.txt
user@user:PPT-Examples] bc < test.txt # The file contents is passed as input
3
user@user:PPT-Examples] rm text.txt # Not needed anymore

Linux Systems
File Specific Cmds & Opers - du
●
du helps us to estimate file space usage
user@user:PPT-Examples] du
44 .
user@user:PPT-Examples] du -h # Human readable
44K .
user@user:PPT-Examples] du -sb * # Size in bytes
301 10_cmd_line_args.sh
416 1_expressions.sh
139 2_if_then.sh
200 3_if_elif.sh
405 4_string_test.sh
427 5_logical_operators.sh
187 6_case_statements.sh
131 7_for_loop.sh
103 8_while_loop.sh
436 9_arrays.sh

Linux Systems
File Specific Cmds & Opers - df
●
df helps us to fine system disk space usage
user@user:PPT-Examples] df
tmpfs 803976 9520 794456 2% /run
/dev/sda1 76765204 9557568 63285052 14% /
tmpfs 4019868 8484 4011384 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 4019868 0 4019868 0% /sys/fs/cgroup
/dev/sda6 519987072 71655932 421847532 15% /home
tmpfs 803976 60 803916 1% /run/user/1001
user@user:PPT-Examples] df -h # Human readable
udev 3.9G 0 3.9G 0% /dev
tmpfs 786M 9.3M 776M 2% /run
/dev/sda1 74G 9.2G 61G 14% /
tmpfs 3.9G 8.3M 3.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
/dev/sda6 496G 69G 403G 15% /home
tmpfs 786M 60K 786M 1% /run/user/1001

Linux Systems
File Specific Cmds & Opers - df
●
df helps us to find system disk space usage
user@user:PPT-Examples] df # Note the output depends on the installation
tmpfs 803976 9520 794456 2% /run
/dev/sda1 76765204 9557568 63285052 14% /
tmpfs 4019868 8484 4011384 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 4019868 0 4019868 0% /sys/fs/cgroup
/dev/sda6 519987072 71655932 421847532 15% /home
tmpfs 803976 60 803916 1% /run/user/1001
user@user:PPT-Examples] df -h # Human readable
udev 3.9G 0 3.9G 0% /dev
tmpfs 786M 9.3M 776M 2% /run
/dev/sda1 74G 9.2G 61G 14% /
tmpfs 3.9G 8.3M 3.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
/dev/sda6 496G 69G 403G 15% /home
tmpfs 786M 60K 786M 1% /run/user/1001

Linux Systems
File Specific Cmds & Opers - stat
●
stat helps us to display file or file system status
user@user:PPT-Examples] stat 1_expression.sh
File: '1_expressions.sh'
Size: 416 Blocks: 8 IO Block: 4096 regular file
Device: 806h/2054d Inode: 23600973 Links: 1
Access: (0777/-rwxrwxrwx) Uid: ( 1001/ adil_sk) Gid: ( 1001/ adil_sk)
Access: 2018-12-03 16:24:18.489886098 +0530
Modify: 2018-12-03 14:24:00.896270594 +0530
Change: 2018-12-03 14:29:10.811075929 +0530
Birth: -

Linux Systems
File Specific Cmds & Opers - ln
●
ln helps us to make links between file
●
Two types of links are possible
– Hard link only on files→ Directory
●
The link file has the same inode number
●
Doesn’t matter if the original file get deleted
●
It a default link created
– Soft link both on files and directories→ Directory
●
The link file has the different inode number
●
If the original file is deleted the link get broken
●
Created with -s option

Linux Systems
File Specific Cmds & Opers – ln – Hard link
user@user:PPT-Examples] cat test.txt
Hello
user@user:PPT-Examples] ln test.txt hard_link.txt # Default is hardlink
user@user:PPT-Examples] cat hard_link.txt
Hello
user@user:PPT-Examples] echo World >> hard_link.txt
Hello
World
user@user:PPT-Examples] stat text.txt | head -3
File: 'text.txt'
user@user:PPT-Examples] stat hard_link.txt | head -3
File: 'hard_link.txt'
user@user:PPT-Examples] rm text.txt # Doesn’t effect the hard link!!
user@user:PPT-Examples] cat hard_link.txt
Hello
World

Linux Systems
File Specific Cmds & Opers – ln – Soft link
user@user:PPT-Examples] ln -s test.txt soft_link.txt
user@user:PPT-Examples] ls -l soft_link.txt
lrwxrwxrwx 1 user user 8 Dec 4 15:01 soft_link.txt -> test.txt
user@user:PPT-Examples] cat soft_link.txt
Hello
user@user:PPT-Examples] echo World >> soft_link.txt
Hello
World
user@user:PPT-Examples] stat text.txt | head -3
File: 'text.txt'
user@user:PPT-Examples] stat hard_link.txt | head -3
File: 'soft_link.txt'
user@user:PPT-Examples] rm text.txt # This effects the soft link!!
user@user:PPT-Examples] cat soft_link.txt
cat: soft_link.txt: No such file or directory
user@user:PPT-Examples] ls -l soft_link.txt # Broken link!!
lrwxrwxrwx 1 user user 8 Dec 4 15:01 soft_link.txt -> test.txt

Linux Systems
Shell Scripting - Loops – for
●
The structure is a looping structure. Used to execute a
set of commands while the provided list is empty
●
The loop terminates as soon as the all the elements in
the list is evaluated
●
Can be used in multiple methods, an example for fixed
iteration is show below
for i in list
do
Code Block
done
Syntax

Linux Systems
Shell Scripting - Loops – for
1 #!/bin/bash
2
3 for i in 1 2 3 4 5
4 do
5 echo "Loop counter is ${i}"
6 done
~
"7_for_loop.sh" 6L, 70C 0,0-1 All
user@user:PPT-Examples] vi 7_for_loop.sh
user@user:PPT-Examples] chmod +x 7_for_loop.sh
user@user:PPT-Examples] ./7_for_loop.sh
Loop counter is 1
Loop counter is 2
Loop counter is 3
Loop counter is 4
Loop counter is 5

Linux Systems
Shell Scripting - Loops – while
●
The structure is a looping structure. Used to execute a
set of commands while a specified condition is true
●
The loop terminates as soon as the condition becomes
false. If condition never becomes false, loop will never
exit
●
Any valid conditional expression will work in the while
loop.
while [ condition ]
do
Code Block
done
Syntax

Linux Systems
Shell Scripting - Loops – while
1 #!/bin/bash
2
3 LOOP=1
4
5 while [ ${LOOP} -le 5 ]
6 do
7 echo "Looping : ${LOOP}"
8 LOOP=$((${LOOP} + 1))
9 done
~
"8_while_loop.sh" 9L, 103C 0,0-1 All
user@user:PPT-Examples] vi 8_while_loop.sh
user@user:PPT-Examples] chmod +x 8_while_loop.sh
user@user:PPT-Examples] ./8_while_loop.sh
Looping : 1
Looping : 2
Looping : 3
Looping : 4
Looping : 5

Linux Systems
Shell Scripting - Arrays
●
An array is a variable containing multiple values may be
of same type or of different type
●
There is no maximum limit to the size of an array
●
Array index starts with zero

Linux Systems
Shell Scripting - Arrays
1 #!/bin/bash
2 LINUX_DISTROS=('Debian' 'Redhat' 'Ubuntu' 'Suse' 'Fedora');
3 echo "Number of elements in the array: ${#LINUX_DISTROS[@]}"
4 echo -e "Printing elements of array in one shottt: ${LINUX_DISTROS[@]}"
5 echo -e "Printing elements of array in one shottt: ${LINUX_DISTROS[*]}"
6 echo -en "Printing elements of array in using a loopt:"
7 for i in ${LINUX_DISTROS[@]}
8 do
9 echo -n ${i}” “
10 done; echo
~
"9_arrays.sh" 10L, 436C 0,0-1 All
user@user:PPT-Examples] vi 9_arrays.sh
user@user:PPT-Examples] chmod +x 9_arrays.sh
user@user:PPT-Examples] ./9_arrays.sh
Number of elements in the array: 5
Printing elements of array in one shot : Debian Redhat Ubuntu Suse Fedora
Printing elements of array in one shot : Debian Redhat Ubuntu Suse Fedora
Printing elements of array in using a loop : Debian Redhat Ubuntu Suse Fedora

Linux Systems
Shell Scripting – Command Line Arguments
●
Shell script can accept command-line arguments & options
just like other Linux commands
●
Within your shell script, you can refer to these arguments as
$1,$2,$3,.. & so on.
●
Then the command line arguments are executed like
●
Read all command line arguments and print them

Linux Systems
Shell Scripting - Command Line Arguments
1 #!/bin/bash
2
3 if [ $# != 2 ]
4 then
5 echo "Usage: Pass 2 arguments"
6 exit 0
7 fi
8
9 echo "The arguments of the script you passed are:"
10 echo "Total number of arguments you passed are : $#"
11 echo "The name of the script is : $0"
12 echo "The first argument is : $1"
13 echo "The second argument is : $2"
~
"10_cmd_line_args.sh" 13L, 301C 0,0-1 All
user@user:PPT-Examples] vi 10_cmd_line_args.sh

Linux Systems
Shell Scripting - Command Line Arguments
user@user:PPT-Examples] chmod +x 10_cmd_line_args.sh
user@user:PPT-Examples] ./10_cmd_line_args.sh Hello 1234
The arguments of the script you passed are:
Total number of arguments you passed are : 2
The name of the script is : ./10_cmd_line_args.sh
The first argument is : Hello
The second argument is : 1234

Linux Systems
Shell Scripting - Functions
●
Writing functions can greatly simplify a program
●
Improves modularity, readability and maintainability
●
However speed will get slowed down
●
Arguments are accessed as $1, $2, $3…
function name()
{
<command>
<statments>
<expression>
}
Syntax

Linux Systems
Shell Scripting - Functions
1 #!/bin/bash
2
3 function sum()
4 {
5 x=`expr $1 + $2`
6 echo $x
7 }
8
9 y=`sum 5 3`
10 echo "The sum is 5 and 3 is $y"
11 echo "The sum is 6 and 2 is `sum 6 2`"
~
"11_functions.sh" 11L, 146C 0,0-1 All
user@user:PPT-Examples] vi 11_functions.sh
user@user:PPT-Examples] chmod +x 11_functions.sh
user@user:PPT-Examples] ./11_functions.sh
The sum is 5 and 3 is 8
The sum is 6 and 2 is 8

Linux Systems
User Specific Commands – useradd and su
●
All Accesses into a Linux System are through a User
●
Super user (root) will have higher privileges
●
useradd helps us to create a new user or update default new
user information
user@user:~] useradd pingu
useradd: Permission denied.
useradd: cannot lock /etc/passwd; try again later.
user@user:~] sudo useradd pingu
[sudo] password for user:
user@user:~]
●
su to change user ID or become superuser
user@user:~] su - pingu # Note, we did not set the password yet
Password:
●
We need to set the password!. Refer the next slide

Linux Systems
User Specific Commands –passwd
●
So, lets set the password for the user using passwd which is
used to change user password
●
Terminate the prompt by CTRL D and follow the below
command
●
One simple method to solve the above issue is to re create the
user again

Linux Systems
User Specific Commands – userdel
●
userdel to delete a user account and related files

Linux Systems
User Specific Commands – w, who, whoami
●
w shows who is logged on and what they are doing
●
who shows who is logged on
●
whoami prints effective userid

Linux Systems
User Specific Commands – scp
●
scp secure copy (remote file copy program)
●
The authenticity message come whenever there is new user is
found
●
You will have to add -r in case of directories
●
You may provide the destiny path after the : so that the file
gets copied in the provided path

Linux Systems
User Specific Commands – ssh
●
ssh OpenSSH SSH client (remote login program)
●
Well both scp and ssh requires some network information like
and all, so lets see some basic network related commands

Linux Systems
Network Related Commands – ifconfig
●
ifconfig to configure a network interface

Linux Systems
Network Related Commands – ping
●
ping send ICMP ECHO_REQUEST to network hosts

Linux Systems
File Specific Commands – sort
●
sort lines of text files
●
You may even use pipes

Linux Systems
File Specific Commands – uniq
●
uniq used to report or omit repeated lines

Linux Systems
File Specific Commands – cmp
●
cmp to compare two files byte by byte

Linux Systems
File Specific Commands – diff
●
diff to compare files line by line

Linux Systems
Types of Files
●
In Linux system there are different types of files
●
Every file belongs to different group and has different
permissions
●
The below example shows the different types of files
available in Linux
permissions
owner
& group
file
size
created date
& time
file name

Linux Systems
Types of Files
Directory
Block
Character
Soft Link
FIFO (=)
Plain Text
Socket

Linux Systems
Types of Files
r → Read 100 - 4
w → Write 010 - 2
x E→ xecute 001 - 1

Linux Systems
Types of Files
others
group
user

Linux Systems
File Specific Commands – chmod
●
chmod used to change file mode bits
user@user:~] touch test.txt
user@user:~] ls -l test.txt
-rw-rw-r-- 1 user user 0 Dec 10 18:40 test.txt
user@user:~] chmod 777 test.txt
-rwxrwxrwx 1 user user 0 Dec 10 18:40 test.txt
user@user:~] chmod 707 test.txt
-rwx---rwx 1 user user 0 Dec 10 18:40 test.txt
user@user:~] chmod -x test.txt
-rw-rw-rw- 1 user user 0 Dec 10 18:40 test.txt
user@user:~] chmod o+x test.txt
-rw-rwxrw- 1 user user 0 Dec 10 18:40 test.txt
user@user:~] chmod a-r test.txt
--w--wx-w- 1 user user 0 Dec 10 18:40 test.txt
user@user:~]

Linux Systems
File Specific Commands – chown
●
chown used to file owner and group
●
-rw-rw-r-- 1 user user 0 Dec 10 18:40 test.txt
user@user:~] sudo chown user.nobody test.txt
-rw-rw-r-- 1 user nobody 0 Dec 10 18:40 test.txt
user@user:~] mkdir TBD # To Be Deleted
user@user:~] touch TBD/{1..4}.txt # Just create 4 files
user@user:~] ls -l TBD
total 0
-rw-rw-r-- 1 user user 0 Dec 10 19:01 1.txt
user@user:~] sudo chown user.nobody -R TBD # Recursive, since directory
user@user:~] ls -l TBD
total 0
-rw-rw-r-- 1 user nobody 0 Dec 10 19:01 1.txt
user@user:~] rm -fr TBD/ test.txt # Just remove the stray contents
user@user:~]

Linux Systems
Regular Expression
●
Regular expressions = search (and replace / modify /
remove) pattern
●
In theoretical computer science regular expressions
are called as regex or regexp
●
It is a sequence of characters that forms a search
pattern using some special characters
●
Popular applications in Linux (Vi editor, Grep, Sed,
Lex & Yacc etc..) extensively use regular expressions
●
Extensively used in compiler design and
implementation
●
Our idea is to understand them from Linux commands

Linux Systems
Regular Expression
●
Each character in a regular expression is either
understood to be a meta-character with its special
meaning
●
Or a regular character with its literal meaning
●
Together they form a pattern. Some popular & most
frequently used examples are provided below
Meta-character Meaning
? Zero or one occurrence
* Zero or more occurrence
+ One or more occurrence

Linux Systems
Search Commands – find
●
find to search for files in a directory hierarchy
●user@user:~] mkdir -p TBD/Dir1
user@user:~] touch TBD/Dir1/{1..4}.txt
user@user:~] mkdir TBD/Dir2
user@user:~] echo hello > TBD/Dir2/non_empty_file.txt
user@user:~] echo ls > TBD/Dir2/my_ls.sh
user@user:~] chmod +x TBD/Dir2/my_ls.sh
user@user:~] cd TBD
user@user:TBD] find . -print # Prints the contents of current directory
.
./Dir2
./Dir2/non_empty_file.txt
./Dir2/my_ls.sh
./Dir1
./Dir1/1.txt
./Dir1/4.txt
./Dir1/2.txt
./Dir1/3.txt
user@user:TBD] find . -name 1.txt
./Dir1/1.txt
user@user:TBD] find . -name *.sh
./Dir2/my_ls.sh
user@user:TBD]

Linux Systems
Search Commands – find
user@user:TBD] find . -empty
./Dir1/1.txt
./Dir1/4.txt
./Dir1/2.txt
./Dir1/3.txt
user@user:TBD] find . ! -empty
.
./Dir2
./Dir2/non_empty_file.txt
./Dir2/my_ls.sh
./Dir1
user@user:TBD] find . -type f -executable
./Dir2/my_ls.sh
user@user:TBD] find ../ -type d -name Dir1
../TBD1/Dir1
user@user:TBD]

Linux Systems
Search Commands – grep
●
grep to print lines matching a pattern
●
Get Regular Expression And Print (GREP)
●
Is a pattern matching tool used to search the name input file
user@user:TBD] echo -e “ApplenGrapesnBanana” > Dir1/1.txt
user@user:TBD] echo -e “Raw BanananCarrotnTomato” > Dir1/2.txt
user@user:TBD] echo -e “BanglesnCardnToothpick” > Dir1/3.txt
user@user:TBD] grep Apple Dir1/1.txt
Apple
user@user:TBD] grep -r Apple . # Search Apple at the given path.
Dir1/1.txt:Apple
user@user:TBD] grep -r Ban # Default path is current diretory
Dir1/1.txt:Banana
Dir1/2.txt:Raw Banana#
Dir1/3.txt:Bangles
user@user:TBD] grep -r Banana
Dir1/1.txt:Banana
Dir1/2.txt:Raw Banana
user@user:TBD] grep -rx Banana # Match only the given pattern
Dir1/1.txt:Banana
user@user:TBD]

Linux Systems
Search Commands – grep
user@user:TBD] grep -rv Ban # Search everything except Ban
Dir2/non_empty_file.txt:hello
Dir2/my_ls.sh:ls
Dir1/1.txt:Apple
Dir1/1.txt:Grapes
Dir1/2.txt:Carrot
Dir1/2.txt:Tomato
Dir1/3.txt:Bangles
Dir1/3.txt:Card
Dir1/3.txt:Toothpick
user@user:TBD] grep -r Car
Dir1/3.txt:Card
user@user:TBD] grep -ri Car # Ignore case
Dir1/2.txt:carrot
Dir1/3.txt:Card
user@user:TBD] grep -rin Ban # Show line numbers
Dir1/1.txt:3:Banana
Dir1/2.txt:1:Raw Banana
Dir1/3.txt:1:Bangles
user@user:TBD]

Linux Systems
Substitute Command – sed
●
sed is a stream editor for filtering and transforming text
●
It can be a file, or input from a pipe
user@user:TBD] sed ‘s/Apple/apple/’ Dir1/1.txt # Doesn’t change in file!
apple
Grapes
Banana
user@user:TBD] cat Dir1/1.txt
Apple
Grapes
Banana
user@user:TBD] sed -i ‘s/Apple/apple/’ Dir1/1.txt # Saves into the file
apple
Grapes
Banana
user@user:TBD] sed '3s/a/A/' Dir1/1.txt
apple
Grapes
BAnana
user@user:TBD]

Linux Systems
Substitute Command – sed
user@user:TBD] sed '3s/a/A/g' Dir1/1.txt # Change globally
apple
Grapes
BAnAnA
user@user:TBD] echo -e “MangonPineapple” >> Dir1/1.txt
Apple
Grapes
Banana
Mango
Pineapple
user@user:TBD] sed -n ‘2,4p’ Dir1/1.txt
Grapes
Banana
Mango
user@user:TBD] sed ‘2,4d’ Dir1/1.txt
Apple
Pineapple
user@user:TBD]

Linux Systems
Substitute Command – cut
●
cut is used to remove sections from each line of files
user@user:TBD] cat > database.txt # Use CTRL-D to end
Tingu, 9783422342, tingu@gmail.com
Pingu, 9744527342, pingu@gmail.com
Zingu, 9993234455, zingu@gmail.com
user@user:TBD] cat database.txt
user@user:TBD] cut -d"," -f1 database.txt # Cut 1st
field
Tingu
Pingu
Zingu
user@user:TBD] cut -d"," -f2,3 database.txt # Cut 2nd
and 3rd
field
9783422342, tingu@gmail.com
9744527342, pingu@gmail.com
9993234455, zingu@gmail.com
user@user:TBD] cut -c5 database.txt # Cut 5th
character
u
u
u
user@user:TBD]

Linux Systems
Substitute Command – cut
●
Many more interesting combinations are possible
●
You use the piped outputs to cut
user@user:TBD] cut -c5 --complement database.txt # Get all except 5th
char
Ting, 9783422342, tingu@gmail.com
Ping, 9744527342, pingu@gmail.com
Zing, 9993234455, zingu@gmail.com
user@user:TBD] cut -c8-11 database.txt # Get a range from 8th
to 11th
chars
9783
9744
9993
user@user:TBD]
user@user:TBD] dmesg | tail -5 | cut -c1-15 # Get only the kernel time stamp
[ 1378.145670]
[ 1378.145685]
[ 1378.145695]
[ 1378.145935]
[ 1378.145952]
user@user:TBD]

Linux Systems
Substitute Command – split
●
split is used to split a file into pieces
user@user:TBD] mkdir TBD # Just to collect all the splited files
user@user:TBD] cat database.txt
user@user:TBD] split database.txt TBD/ # Split into files
user@user:TBD] ls TBD
aa
user@user:TBD] split -1 database.txt TBD/ # Split every line into a file
aa ab ac
user@user:TBD] cat TBD/aa
user@user:TBD] cat TBD/ac
user@user:TBD] split -b5 database.txt T1BD # Split every 5 bytes into a file
aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as
at au
user@user:TBD] cat TBD/aa # Has 5 bytes from 1st
line
Tinguuser@user:TBD] cat TBD/ab # Has next 5 bytes from 1st
line and it goes on
, 978user@user:TBD]

Linux Systems
Substitute Command – tr
●
tr translates or deletes characters
user@user:TBD] echo hello how are you | tr -d h # Delete all ‘h’
ello ow are you
user@user:TBD] echo hello how are you | tr [:space:] t
Hello how are you
user@user:TBD] echo "my age is 99" | tr -d [:digit:]
my age is
user@user:TBD] tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
Hello
HELLO
user@user:TBD] tr ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz
Hello
hello
user@user:TBD] echo "Heelllooo" | tr -s elo
Helo
user@user:TBD]

Linux Systems
File Compression
●
Compression is needed to conserve the disk space
●
When there is a need to send large files as an attachment via
the email, it is good practice to compress first
●
Compression & Decompression utilities - gzip & gunzip(.gz)
●
The degree of compression depends on
– The type of the file
– Its size
– Compression program used
●
Example
– Html files compress more
– GIF & JPEG image files compress very less, as they are already in
compressed form

Linux Systems
File Compression - Flow
file
gzip
file.gz
file.gz
gunzip
file
Compression flow De-compression flow
• Recursive compression and de-compression (-r option), will come handy
• gzip –r <directory> : To compress files in whole directory
• gunzip –r <directory> : To de-compress files in whole directory

Linux Systems
File Compression – gzip and gunzip
user@user:TBD] ls
Dir1 Dir2
user@user:TBD] ls Dir1
1.txt 2.txt 3.txt 4.txt
user@user:TBD] gzip Dir1/1.txt # Compress the file
1.txt.gz 2.txt 3.txt 4.txt
user@user:TBD] gunzip Dir1/1.txt.gz # Decompress the file
user@user:TBD] gzip -r Dir1
1.txt.gz 2.txt.gz 3.txt.gz 4.txt.gz
user@user:TBD] gunzip -r Dir1/ # Decompress the file
user@user:TBD]

Linux Systems
File Archival
●
Used for creating disk archive that contains a group of files or
an entire directory structure
●
An archive file is a collection of files and directories that are
stored in one file
●
Archive file is not compressed, it uses the same amount of disk
space as all the individual files and directories
●
In case of compression, compressed file occupies lesser space
●
Combination of archival & compression also can be done
• File archival is achieved using ‘tar’ with the following commands:
• tar -cvf <archive name> <file-names>
• tar -xvf <archive name>

Linux Systems
File Archival - Flow
file1, file2,
file3
tar -cvf
file.tar
gzip file.tar
file.tar.gz
file.tar.gz
gunzip
file.tar
tar -xvf
file1, file2,
file3
Archival
De-compression
Compression Untar

Linux Systems
File Archival – tar
user@user:TBD] ls
Dir1 Dir2
user@user:TBD] tar cvf dir1.tar Dir1/ # Archive Dir1 as dir1.tar
Dir1/
Dir1/1.txt
Dir1/4.txt
Dir1/2.txt
Dir1/3.txt
user@user:TBD] ls
Dir1 dir1.tar Dir2
user@user:TBD] rm -fr Dir1
user@user:TBD] ls
dir1.tar Dir2
user@user:TBD] tar xvf dir1.tar
Dir1/
Dir1/1.txt
Dir1/4.txt
Dir1/2.txt
Dir1/3.tx
user@user:TBD] ls
Dir1 dir1.tar Dir2
user@user:TBD]

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