session-09.txt

Linux
Expenses project

Shell Script
------------------
3 servers....

configuring the server?
------------------------
installed application runtime --> nodejs
downloaded code
created a directory
created a user for our application
unzip the code
installed node js dependencies
created systemctl service
configured mysql details
start the server

MySQL
----------
install mysql server
configure password
start the server

frontend
-----------
install nginx
start nginx
downloaded the code
unzipped
configured backend details
start the server

15min
20 servers --> 30min

10-15min

Deployment
------------
releasing new version

download andriod latest version
switch off phone
install latest version
start the phone

upgrade/releasing/deploying the new application
---------------
download the new code
stop the server
remove old code
copy the new code
start the server

logs in field
---------------
carry one log at a time manually to home...
hire a tractor, keep all logs at a time...

run commands one by one --> manual
keep all commands in a file and run that file --> shell script
------------------------------
shell runs these commands in sequence...

errors may defnitely come
-------------------------
if error
	you ignore?
	you clear error and go forward
	
we need to check if the present command got success or not?

if success go forward
if failure, exit the program

programming/developing scripting
---------------------------
Coding
	1. Programming/Developing --> reactjs, nodejs, java, .net, python, etc.
	2. Scripting
		automating manual tasks other than development
			server configuration
			installations
			deployment process
	
execution time should be less
memory consumption should be less
	data structures
	alogorithms
	design patterns
	
	connect to DB
	fetch the data asap..
	transaction management
	
Coding concepts
-----------------
variables
data types --> less priority in scripting
functions
loops
conditions


Algorithm
-----------------
1. fast releases
2. reduce the defects

write down the steps in general way...
I will install a package through script

1. check the package is already installed or not
	if installed that's all
2. if not installed
	then you need to install
3. just verify is it done properly or not
	if good, that's all
	otherwise check and clear the error
	
if sunday, dont go to school, otherwise go to school
-------------------------------------------------
1. check what day is today..
2. if today is not sunday, just go to school.
3. otherwise enjoy the holiday.

today=wednesday
if(today==sunday){
	print enjoy the holiday
}
else{
	print go to school
}

what is shell?
----------------
ls -l --> getting result
lss -l --> who is checking that it is wrong?

it's nothing but shell

shell is the CLI that interprets the linux commands and executes them

terminal == shell terminal

shell script --> keeping all the commands you need in a file with variables, conditions, loops, functions, etc is called shell script

shell interprets and executes shell script.

Where to store scripts?
------------------------
can you store in your laptop?
	security and backup --> if laptop crashes
	versions --> you must keep the previous versions
	collobaration -->
	
to store our shell scripts in github

repository --> stores something...
github --> only store code

git vs github vs gitlab

Linux --> kernel
Redhat, ubuntu --> implementations of linux kernel from different vendors

git --> linus torvalds...concept
github gitlab bitbucket -->implementations of git from different vendors

one repo one specific code...

steps
-----------
1. create repo in github
2. clone in your local laptop

where to develop the code?
-------------------
can I develop code using vim editor?

IDE --> integrated development environment/editor

vs code --> light weight and perfect for scripting
eclipse
intelliJ
sublime editor

1