DEV Community: Prajwal k

Linux and Bash Command Cheat Sheet: The Basics

Prajwal k — Sun, 26 Jun 2022 16:45:18 +0000

Getting information

Return your user name

whoami

Return your user and group id

id

Return operating system name, username, and other info

uname -a

Display reference manual for a command

man top

Get help on a command

curl --help

Return the current date and time

date

Monitoring performance and status

List selection of or all running processes and their PIDs

ps
ps -e

Display resource usage

top

List mounted file systems and usage

df

Working with files

Copy a file

cp file.txt new_path/new_name.txt

Change file name or path

mv this_file.txt that_path/that_file.txt

Remove a file verbosely

rm this_old_file.txt -v

Create an empty file, or update existing file's timestamp

touch a_new_file.txt

Change/modify file permissions to 'execute' for all users

chmod +x my_script.sh

Get count of lines, words, or characters in file

wc -l table_of_data.csv
wc -w my_essay.txt
wc -m some_document.txt

Return lines matching a pattern from files matching a filename pattern - case insensitive and whole words only

grep -iw hello \*.txt

Return file names with lines matching the pattern 'hello' from files matching a filename pattern

grep -l hello \*.txt

Navigating and working with directories

List files and directories by date, newest last

ls -lrt

Find files in directory tree with suffix 'sh'

find -name '\*.sh'

Return present working directory

pwd

Make a new directory

mkdir new_folder

Change the current directory: up one level, home, or some other path

cd ../
cd ~ or cd
cd another_directory

remove directory, verbosely

Printing file and string contents

Print file contents

cat my_shell_script.sh

Print file contents page-by-page

more ReadMe.txt

Print first N lines of file

head -10 data_table.csv

Print last N lines of file

tail -10 data_table.csv

Print string or variable value

echo "I am not a robot"
echo "I am $USERNAME"

Compression and archiving

Archive a set of files

tar -cvf my_archive.tar.gz file1 file2 file3

Compress a set of files

zip my_zipped_files.zip file1 file2
zip my_zipped_folders.zip directory1 directory2

Extract files from a compressed zip archive

unzip my_zipped_file.zip
unzip my_zipped_file.zip -d extract_to_this_direcory

Performing network operations

Print hostname

hostname

Send packets to URL and print response

ping www.google.com

Display or configure system network interfaces

ifconfig
ip

Display contents of file at a URL

curl <url>

Download file from a URL

wget <url>

Bash shebang

!/bin/bash

Pipes and Filters

Chain filter commands using the pipe operator

ls | sort -r

Pipe the output of manual page for ls to head to display the first 20 lines

man ls | head -20

Shell and Environment Variables

List all shell variables

set

Define a shell variable called my_planet and assign value Earth to it

my_planet=Earth

Display shell variable

echo $my_planet

List all environment variables

env

Environment vars: define/extend variable scope to child processes

export my_planet
export my_galaxy='Milky Way'

Metacharacters

Comments

# The shell will not respond to this message

Command separator

echo 'here are some files and folders'; ls

File name expansion wildcard

ls *.json

Single character wildcard

ls file_2021-06-??.json

Quoting

Single quotes - interpret literally

echo 'My home directory can be accessed by entering: echo $HOME'

Double quotes - interpret literally, but evaluate metacharacters

echo "My home directory is $HOME"

Backslash - escape metacharacter interpretation

echo "This dollar sign should render: \$"

I/O Redirection

Redirect output to file

echo 'Write this text to file x' > x

Append output to file

echo 'Add this line to file x' >> x

Redirect standard error to file

bad_command_1 2> error.log

Append standard error to file

bad_command_2 2>> error.log

Redirect file contents to standard input

$ tr “[a-z]” “[A-Z]” < a_text_file.txt

The input redirection above is equivalent to

$cat a_text_file.txt | tr “[a-z]” “[A-Z]”

Command Substitution

Capture output of a command and echo its value

THE_PRESENT=$(date)
echo "There is no time like $THE_PRESENT"

Command line arguments

./My_Bash_Script.sh arg1 arg2 arg3

Batch vs. concurrent modes
Run commands sequentially

start=$(date); ./MyBigScript.sh ; end=$(date)

Run commands in parallel

./ETL_chunk_one_on_these_nodes.sh & ./ETL_chunk_two_on_those_nodes.sh

Scheduling jobs with Cron

Open crontab editor

crontab -e

Job scheduling syntax

m h dom mon dow command

minute, hour, day of month, month, day of week
'*' means any

Append the date/time to file every Sunday at 6:15 pm

15 18 * * 0 date >> sundays.txt

Run a shell script on the first minute of the first day of each month

1 0 1 * * ./My_Shell_Script.sh

Back up your home directory every Monday at 3 am

0 3 * * 1 tar -cvf my_backup_path\my_archive.tar.gz $HOME\

Deploy your cron job

Close the crontab editor and save the file

List all cron jobs

crontab -l

📝 Learn JavaScript the right way with this beginner's cheat sheet

Prajwal k — Fri, 10 Jun 2022 16:02:08 +0000

Fundamentals
Variables
Data Types
Operators
Functions
Array
Loops
If-Else
Strings
Regular Expression
Data Transformation
Dealing with Dates in JavaScript
Document Object Model (DOM) in JavaScript
JavaScript Numbers & Math
Events
Error
Working With Browser

1. JavaScript Fundamentals

Here are the basics on how to add JavaScript to your website.

In HTML code, JavaScript is written as follows:

Adding JavaScript code to an HTML page requires it to be enclosed within the <script> tag as shown below:

<script type = "text/javascript">
//JavaScript coding can be done inside this tag
</script>

Using this input, the browser can correctly identify and execute the code.

Including external JavaScript files in an HTML file:

It is also possible to create a separate JavaScript file and include it within our HTML file.

Keeping different types of code separate will result in better-organized files, and different kinds of codes can be kept isolated from one another.

We can, for example, include our JavaScript code in our HTML file in the following manner if our JavaScript code is in the file script.js:

<script src="script.js"></script>

Including Comments:

Leaving comments in your code helps other people understand what you're doing or reminds you if you've forgotten something.
Note: To prevent the browser from trying to execute them, they must be properly marked.

In JavaScript you have two different options:

Single-line comments— Whenever you want to include a comment that is limited to a single line, precede it with //
Multi-line comments — If you want to include a long comment between several lines, wrap it in /* and */ to avoid it being executed

2. JavaScript Variables

JavaScript variables are simply storage locations named by their names.

Thus, we can use them in our JavaScript codes as stand-in values through which we can perform various operations.

There are three ways to use variables in JavaScript:
var — The most common variable. It can be reassigned but only accessed within a function. with var move to the top when the code is executed.

var x = 140; //  variable x can be reassigned a new value and also redeclared

const — Cannot be reassigned and are not accessible until they appear in a program.

const x = 5; // variable x cannot be reassigned a new value or redeclared

let— Like const, the let variable can be reassigned but not re-declared.

let x = 202; // variable x cannot be redeclared but can be reassigned a new value

3. JavaScript Data Types

Variables in JavaScript can store a variety of values and data. You use the equals to "=" operator to assign values to JavaScript variables. JavaScript has the following data types:

Numbers: These can either be real numbers or integers.

var id = 50

Variables: Unlike a fixed value, a variable data type does not have a fixed value.

var x

Text (strings): Strings are the most basic types of JavaScript data.

var demoString = "Hello! World"

Operations: JavaScript variables can be assigned operations.

var mul = 10*9

Boolean Values: True or false are the only two types of Boolean values.

var booleanValue = true

Constant numbers: These data types have a constant value.const

l = 8.8

JavaScript objects: These are containers for properties that have names. JavaScript objects have methods and members.

var name = {name:"Jon Snow", id:"AS123"}

4. JavaScript Operators

Having variables allows you to perform various types of operations on them. Operators allow you to do this.

There are 4 types of Operators

Fundamental Operators:

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
(...)	Grouping operator, operations within brackets are executed earlier than those outside
%	Modulus (remainder )
++	Increment numbers
--	Decrement numbers

Bitwise Operators:

Operator	Description
&	AND statement

~	NOT
^	XOR
<<	Left shift
>>	Right shift
>>>	Zero fill right shift

Comparison Operators:

Operator	Description
==	Equal to
===	Equal value and equal type
!=	Not equal
!==	Not equal value or not equal type
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to
?	Ternary operator

Logical Operators:

Operator	Description
&&	Logical and

!	Logical not

5. JavaScript Functions

The JavaScript function is a block of code that performs a particular task. They look like this:

function nameOfTheFunction(parameterOne, parameterTwo, parameterThree, parameterFour,....,parameterN) {
   // Job or Task of the function 
}

Function for outputting data Functions are commonly used to output data. There are several options for the output:

Function	Description
alert()	Output data in an alert box in the browser window
confirm()	Opens up a yes/no dialog and returns true/false
console.log()	Writes information to the browser console, good for debugging purposes
document.write()	Write directly to the HTML document
prompt()	Creates a dialogue for user input

Global Functions Global functions are functions built into every browser capable of running JavaScript.

Function	Description
decodeURI()	Decodes a Uniform Resource Identifier (URI) created by encodeURI or similar
decodeURIComponent()	Decodes a URI component
encodeURI()	Encodes a URI into UTF-8
encodeURIComponent()	Same but for URI components
eval()	Evaluates JavaScript code represented as a string
isFinite()	Determines whether a passed value is a finite number
isNaN()	Determines whether a value is NaN or not
Number()	Returns a number converted from its argument
parseFloat()	Parses an argument and returns a floating-point number
parseInt()	Parses its argument and returns an integer

6. JavaScript Arrays

An array is a special variable, which can hold more than one value:

const cars = ["Saab", "Volvo", "BMW"];

Array Methods:

Which can be used to perform various types of operations.

Methods	Description
pop()	This method is used for removing the last element of an array.
push()	This method is used for adding a new element at the very end of an array.
concat()	This method is used for joining various arrays into a single array.
reverse()	This method is used for reversing the order of the elements in an array.
shift()	This method is used for removing the first element of an array.
slice()	This method is used for pulling a copy of a part of an array into a new array.
splice()	This method is used for adding elements in a particular way and position.
toString()	This method is used for converting the array elements into strings.
unshift()	This method is used for adding new elements at the beginning of the array.
valueOf()	This method is used for returning the primitive value of the given object.
indexOf()	This method is used for returning the first index at which a given element is found in an array.
lastIndexOf()	This method is used for returning the final index at which a given element appears in an array.
join()	This method is used for combining elements of an array into one single string and then returning it.
sort()	This method is used for sorting the array elements based on some condition.

An array is a special variable, which can hold more than one value:

const cars = ["Saab", "Volvo", "BMW"];

7. JavaScript Loops

Almost all programming languages include loops. It allows you to run blocks of code indefinitely with different values:

for loop: JavaScript's most common method for creating loops.

for (initialization of the loop variable; condition checking for the loop; updation after the loop) {
   // code to be executed in loop
}

while loop: Determines when a loop should run. // Initialization of the loop variable is done before the while loop begins

while(condition checking for the loop){
// 1. code to be executed in loop
// 2. updation of the loop variable
}

do-while loop: Similar to the while loop, it runs at least once and checks whether there is a condition to run it again at the end. // Initialization of the loop variable is done before the do-while loop begins

do{
// 1. code to be executed in loop
// 2. updation of the loop variable
}while(condition checking for the loop);

When it comes to loops, there are two important statements:

Continue statement: If certain conditions are met, skip sections of the loop.
break statement: Exit the cycle when a specified condition is met.

8. JavaScript If-Else

If-else is used in JavaScript to execute a block of codes conditionally. These are used to set conditions for your code block to run. There are situations where certain blocks of code are executed, and there are situations where they are not.

if (condition)
{
   // Executes this block if
   // condition is true
}
else
{
   // Executes this block if
   // condition is false
}

9. JavaScript Strings

In JavaScript, strings are used to represent text that does not perform a function but can be displayed.

var Name = "John Cena";

In this case, John Cena is the string.

The following are all the escape sequences in JavaScript, as well as methods that JavaScript provides for strings:

Escape Characters Using single or double quotes, strings are marked in JavaScript. Special characters are needed for quotation marks in a string:

Character	Description
\'	Single quotes
\"	Double quotes
\t	Horizontal tab
\v	Vertical tab
\	Backslash
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return

String methods: Strings can be worked with in many different ways:

Method	Description
charAt()	Returns a character at a specified position inside a string
charCodeAt()	Gives you the Unicode of a character at that position
concat()	Concatenates (joins) two or more strings into one
fromCharCode()	Returns a string created from the specified sequence of UTF-16 code units
indexOf()	Provides the position of the first occurrence of a specified text within a string
lastIndexOf()	Same as indexOf() but with the last occurrence, searching backward
match()	Retrieves the matches of a string against a search pattern
replace()	Find and replace specified text in a string
search()	Executes a search for a matching text and returns its position
slice()	Extracts a section of a string and returns it as a new string
split()	Splits a string object into an array of strings at a specified position
substr()	Similar to slice() but extracts a substring depending on a specified number of characters
substring()	Also similar to slice() but can’t accept negative indices
toLowerCase()	Convert strings to lower case
toUpperCase()	Convert strings to upper case
valueOf()	Returns the primitive value (that has no properties or methods) of a string object

10. JavaScript Regular Expression

Strings can be matched by regular expressions, which are search patterns. They can be used for text search and text replacement.

Pattern Modifiers

Pattern	Description
e	Evaluate replacement
i	Perform case-insensitive matching
g	Perform global matching
m	Perform multiple line matching
s	Treat strings as a single line
x	Allow comments and whitespace in the pattern
U	Ungreedy pattern

Brackets

Operator	Description
[abc]	Find any of the characters between the brackets
[^abc]	Find any character which is not in the brackets
[0-9]	Used to find any digit from 0 to 9
[A-z]	Find any character from uppercase A to lowercase z
(a	b

Metacharacters

Operator	Description
.	Find a single character, except newline or line terminator
\w	Word character
	\W
\d	A digit
\D	A non-digit character
\s	Whitespace character
\S	Non-whitespace character
\b	Find a match at the beginning/end of a word
\B	A match not at the beginning/end of a word
\0	NUL character
\n	A new line character
\f	Form feed character
\r	Carriage return character
\t	Tab character
\v	Vertical tab character
\xxx	The character specified by an octal number xxx
\xdd	Character specified by a hexadecimal number dd
\uxxxx	The Unicode character specified by a hexadecimal number XXXX

Quantifiers

Operator	Description
n+	Matches any string that contains at least one n
n*	Any string that contains zero or more occurrences of n
n?	A string that contains zero or one occurrence of n
n{X}	String that contains a sequence of X n’s
n{X,Y}	Strings that contain a sequence of X to Y n’s
n{X,}	Matches any string that contains a sequence of at least X n’s
n$	Any string with n at the end of it
^n	String with n at the beginning of it
?=n	Any string that is followed by a specific string n
?!n	String that is not followed by a specific string ni

11. Data Transformation

'Data transformation' is the conversion of one format to another. Using higher-order JavaScript functions, you can transform data by taking two or more functions as inputs and returning a function as a consequence. Map(), filter(), and reduce() are all higher-order functions that take a function as input.

Map() By calling a specific function on each element of a parent array, JavaScript's map() method creates an array. Iterating over an array and calling functions on every element is accomplished using

map(), a non-mutating method.
var arr = [10,20,30];
var triple  = arr.map(x => x * 3);
triple; // [30,60,90]

filter() With arr.filter(), a new array is generated that consists only of those elements in a given array that meet a given set of conditions and criteria.

var arr = [13,40,47];
var odd = arr.filter(x => x % 2);
odd; // [13,47]

Reduce() When used in JavaScript, the arr.reduce() method reduces a given array to a single value by running a function provided for each value (from left-to-right), and storing the output in an accumulator.

var arr = [10,20,30];
var counter = 0;
let answer = arr.reduce((accumulator, value) => value + accumulator, counter);
console.log(answer) // answer = 10 + 20 + 30 = 60

12. Dealing with Dates in JavaScript

Dealing with Dates in JavaScript
You can also work with and modify dates and time with JavaScript. This is the next chapter in the JavaScript cheat sheet.

Setting Dates

Methods	Description
Date()	Creates a new date object with the current date and time
Date(2017, 5, 21, 3, 23, 10, 0)	Create a custom date object.
Date("2017-06-23")	Date declaration as a string

Pulling Date and Time Values

Properties	Description
getDate()	Get the day of the month as a number (1-31)
getDay()	The weekday as a number (0-6)
getFullYear()	Year as a four-digit number (yyyy)
getHours()	Get the hour (0-23)
getMilliseconds()	The millisecond (0-999)
getMinutes()	Get the minute (0-59)
getMonth()	Month as a number (0-11)
getSeconds()	Get the second (0-59)
getTime()	Get the milliseconds since January 1, 1970
getUTCDate()	The day (date) of the month in the specified date according to universal time (also available for day, month, full year, hours, minutes etc.)
parse	Parses a string representation of a date and returns the number of milliseconds since January 1, 1970

Set Part of a Date

Properties	Description
setDate()	Set the day as a number (1-31)
setFullYear()	Sets the year (optionally month and day)
setHours()	Set the hour (0-23)
setMilliseconds()	Set milliseconds (0-999)
setMinutes()	Sets the minutes (0-59)
setMonth()	Set the month (0-11)
setSeconds()	Sets the seconds (0-59)
setTime()	Set the time (milliseconds since January 1, 1970)
setUTCDate()	Sets the day of the month for a specified date according to universal time (also available for day, month, full year, hours, minutes etc.)

13. Document Object Model (DOM) in JavaScript

A website's code is organized into Document Object Models (DOMs). JavaScript allows you to build and alter HTML elements (called nodes) in many different ways.

Node Properties

Properties	Description
attributes	Returns a live collection of all attributes registered to an element
baseURI	Provides the absolute base URL of an HTML element
childNodes	Gives a collection of an element’s child nodes
firstChild	Returns the first child node of an element
lastChild	The last child node of an element
nextSibling	Gives you the next node at the same node tree level
nodeName	Returns the name of a node
nodeType	Returns the type of a node
nodeValue	Sets or returns the value of a node
ownerDocument	The top-level document object for this node
parentNode	Returns the parent node of an element
previousSibling	Returns the node immediately preceding the current one
textContent	Sets or returns the textual content of a node and its descendants

Node Methods

Methods	Description
appendChild()	Adds a new child node to an element as the last child node
cloneNode()	Clones an HTML element
compareDocumentPosition()	Compares the document position of two elements
getFeature()	Returns an object which implements the APIs of a specified feature
hasAttributes()	Returns true if an element has any attributes, otherwise false
hasChildNodes()	Returns true if an element has any child nodes, otherwise false
insertBefore()	Inserts a new child node before a specified, existing child node
isDefaultNamespace()	Returns true if a specified namespaceURI is the default, otherwise false
isEqualNode()	Checks if two elements are equal
isSameNode()	Checks if two elements are the same node
isSupported()	Returns true if a specified feature is supported on the element
lookupNamespaceURI()	Returns the namespace URI associated with a given node
lookupPrefix()	Returns a DOMString containing the prefix for a given namespace URI if present
normalize()	Joins adjacent text nodes and removes empty text nodes in an element
removeChild()	Removes a child node from an element
replaceChild()	Replaces a child node in an element

Element Methods

Methods	Description
getAttribute()	Returns the specified attribute value of an element node
getAttributeNS()	Returns string value of the attribute with the specified namespace and name
getAttributeNode()	Gets the specified attribute node
getAttributeNodeNS()	Returns the attribute node for the attribute with the given namespace and name
getElementsByTagName()	Provides a collection of all child elements with the specified tag name
getElementsByTagNameNS()	Returns a live HTMLCollection of elements with a certain tag name belonging to the given namespace
hasAttribute()	Returns true if an element has any attributes, otherwise false
hasAttributeNS()	Provides a true/false value indicating whether the current element in a given namespace has the specified attribute
removeAttribute()	Removes a specified attribute from an element
removeAttributeNS()	Removes the specified attribute from an element within a certain namespace
removeAttributeNode()	Takes away a specified attribute node and returns the removed node
setAttribute()	Sets or changes the specified attribute to a specified value
setAttributeNS()	Adds a new attribute or changes the value of an attribute with the given namespace and name
setAttributeNode()	Sets or changes the specified attribute node
setAttributeNodeNS()	Adds a new namespaced attribute node to an element

14. JavaScript Numbers & Math

Mathematical functions and constants can also be performed in JavaScript.

Number Properties

Properties	Description
MAX_VALUE	The maximum numeric value representable in JavaScript
MIN_VALUE	Smallest positive numeric value representable in JavaScript
NaN	The “Not-a-Number” value
NEGATIVE_INFINITY	The negative Infinity value
POSITIVE_INFINITY	Positive Infinity value

Number Methods

Methods	Description
toExponential()	Returns the string with a rounded number written as exponential notation
toFixed()	Returns the string of a number with a specified number of decimals
toPrecision()	String of a number written with a specified length
toString()	Returns a number as a string
valueOf()	Returns a number as a number

Math Properties

Properties	Description
E	Euler’s number
LN2	The natural logarithm of 2
LN10	Natural logarithm of 10
LOG2E	Base 2 logarithm of E
LOG10E	Base 10 logarithm of E
PI	The number PI
SQRT1_2	Square root of 1/2
SQRT2	The square root of 2

Math Methods

Method	Description
abs(x)	Returns the absolute (positive) value of x
acos(x)	The arccosine of x, in radians
asin(x)	Arcsine of x, in radians
atan(x)	The arctangent of x as a numeric value
atan2(y,x)	Arctangent of the quotient of its arguments
ceil(x)	Value of x rounded up to its nearest integer
cos(x)	The cosine of x (x is in radians)
exp(x)	Value of Ex
floor(x)	The value of x rounded down to its nearest integer
log(x)	The natural logarithm (base E) of x
max(x,y,z,...,n)	Returns the number with the highest value
min(x,y,z,...,n)	Same for the number with the lowest value
pow(x,y)	X to the power of y
random()	Returns a random number between 0 and 1
round(x)	The value of x rounded to its nearest integer
sin(x)	The sine of x (x is in radians)
sqrt(x)	Square root of x
tan(x)	The tangent of an angle

15. JavaScript Events

Events are things that can happen to HTML elements and are performed by the user. The programming language can listen for these events and trigger actions in the code. No JavaScript cheat sheet would be complete without them.

Mouse

Properties	Description
onclick	The event occurs when the user clicks on an element
oncontextmenu	User right-clicks on an element to open a context menu
ondblclick	The user double-clicks on an element
onmousedown	User presses a mouse button over an element
onmouseenter	The pointer moves onto an element
onmouseleave	Pointer moves out of an element
onmousemove	The pointer is moving while it is over an element
onmouseover	When the pointer is moved onto an element or one of its children
onmouseout	User moves the mouse pointer out of an element or one of its children
onmouseup	The user releases a mouse button while over an element

Keyboard

Properties	Description
onkeydown	When the user is pressing a key down
onkeypress	The moment the user starts pressing a key
onkeyup	The user releases a key

Frame

Properties	Description
onabort	The loading of a media is aborted
onbeforeunload	Event occurs before the document is about to be unloaded
onerror	An error occurs while loading an external file
onhashchange	There have been changes to the anchor part of a URL
onload	When an object has loaded
onpagehide	The user navigates away from a webpage
onpageshow	When the user navigates to a webpage
onresize	The document view is resized
onscroll	An element’s scrollbar is being scrolled
onunload	Event occurs when a page has unloaded

Form

Properties	Description
onblur	When an element loses focus
onchange	The content of a form element changes (for , and )
onfocus	An element gets focus
onfocusin	When an element is about to get focus
onfocusout	The element is about to lose focus
oninput	User input on an element
oninvalid	An element is invalid
onreset	A form is reset
onsearch	The user writes something in a search field (for )
onselect	The user selects some text (for and )
onsubmit	A form is submitted

Drag

Properties	Description
ondrag	An element is dragged
ondragend	The user has finished dragging the element
ondragenter	The dragged element enters a drop target
ondragleave	A dragged element leaves the drop target
ondragover	The dragged element is on top of the drop target
ondragstart	User starts to drag an element
ondrop	Dragged element is dropped on the drop target

Clipboard

Properties	Description
oncopy	User copies the content of an element
oncut	The user cuts an element’s content
onpaste	A user pastes the content in an element

Media

Properties	Description
onabort	Media loading is aborted
oncanplay	The browser can start playing media (e.g. a file has buffered enough)
oncanplaythrough	The browser can play through media without stopping
ondurationchange	The duration of the media changes
onended	The media has reached its end
onerror	Happens when an error occurs while loading an external file
onloadeddata	Media data is loaded
onloadedmetadata	Metadata (like dimensions and duration) are loaded
onloadstart	The browser starts looking for specified media
onpause	Media is paused either by the user or automatically
onplay	The media has been started or is no longer paused
onplaying	Media is playing after having been paused or stopped for buffering
onprogress	The browser is in the process of downloading the media
onratechange	The playing speed of the media changes
onseeked	User is finished moving/skipping to a new position in the media
onseeking	The user starts moving/skipping
onstalled	The browser is trying to load the media but it is not available
onsuspend	The browser is intentionally not loading media
ontimeupdate	The playing position has changed (e.g. because of fast forward)
onvolumechange	Media volume has changed (including mute)
onwaiting	Media paused but expected to resume (for example, buffering)

Animation

Properties	Description
animationend	A CSS animation is complete
animationiteration	CSS animation is repeated
animationstart	CSS animation has started

Other

Properties	Description
transitionend	Fired when a CSS transition has completed
onmessage	A message is received through the event source
onoffline	The browser starts to work offline
ononline	The browser starts to work online
onpopstate	When the window’s history changes
onshow	A element is shown as a context menu
onstorage	A Web Storage area is updated
ontoggle	The user opens or closes the element
onwheel	Mouse wheel rolls up or down over an element
ontouchcancel	Screen-touch is interrupted
ontouchend	User’s finger is removed from a touch-screen
ontouchmove	A finger is dragged across the screen
ontouchstart	A finger is placed on the touch-screen

16. JavaScript Errors

When working with JavaScript, different errors can occur. There are several ways of handling them:

Properties	Description
try	Lets you define a block of code to test for errors
catch	Set up a block of code to execute in case of an error
throw	Create custom error messages instead of the standard JavaScript errors
finally	Lets you execute code, after try and catch, regardless of the result

Error Name Values

JavaScript also has a built-in error object. It has two properties:

Properties	Description
name	Sets or returns the error name
message	Sets or returns an error message in a string from

The error property can return six different values as its name:

Methods	Description
EvalError	An error has occurred in the eval() function
RangeError	A number is “out of range”
ReferenceError	An illegal reference has occurred
SyntaxError	A syntax error has occurred
TypeError	A type error has occurred
URIError	An encodeURI() error has occurred

17. JavaScript Working With Browser

Besides HTML elements, JavaScript is also able to take into account the user browser and incorporate its properties into the code.

Window Properties

Methods	Description
closed	Checks whether a window has been closed or not and returns true or false
defaultStatus	Sets or returns the default text in the status bar of a window
document	Returns the document object for the window
frames	Returns all elements in the current window
history	Provides the History object for the window
innerHeight	The inner height of a window’s content area
innerWidth	The inner width of the content area
length	Find out the number of elements in the window
location	Returns the location object for the window
name	Sets or returns the name of a window
navigator	Returns the Navigator object for the window
opener	Returns a reference to the window that created the window
outerHeight	The outer height of a window, including toolbars/scrollbars
outerWidth	The outer width of a window, including toolbars/scrollbars
pageXOffset	Number of pixels the current document has been scrolled horizontally
pageYOffset	Number of pixels the document has been scrolled vertically
parent	The parent window of the current window
screen	Returns the Screen object for the window
screenLeft	The horizontal coordinate of the window (relative to the screen)
screenTop	The vertical coordinate of the window
screenX	Same as screenLeft but needed for some browsers
screenY	Same as screenTop but needed for some browsers
self	Returns the current window
status	Sets or returns the text in the status bar of a window
top	Returns the topmost browser window

Window Methods

Methods	Description
alert()	Displays an alert box with a message and an OK button
blur()	Removes focus from the current window
clearInterval()	Clears a timer set with setInterval()
clearTimeout()	Clears a timer set with setTimeout()
close()	Closes the current window
confirm()	Displays a dialogue box with a message and an OK and Cancel button
focus()	Sets focus to the current window
moveBy()	Moves a window relative to its current position
moveTo()	Moves a window to a specified position
open()	Opens a new browser window
print()	Prints the content of the current window
prompt()	Displays a dialogue box that prompts the visitor for input
resizeBy()	Resizes the window by the specified number of pixels
resizeTo()	Resizes the window to a specified width and height
scrollBy()	Scrolls the document by a specified number of pixels
scrollTo()	Scrolls the document to specified coordinates
setInterval()	Calls a function or evaluates an expression at specified intervals
setTimeout()	Calls a function or evaluates an expression after a specified interval
stop()	Stops the window from loading

Screen Properties

Properties	Description
availHeight	Returns the height of the screen (excluding the Windows Taskbar)
availWidth	Returns the width of the screen (excluding the Windows Taskbar)
colorDepth	Returns the bit depth of the color palette for displaying images
height	The total height of the screen
pixelDepth	The color resolution of the screen in bits per pixel
width	The total width of the screen

🔗PythonMysql_Connection

Prajwal k — Tue, 07 Jun 2022 16:55:31 +0000

MysqlPythonConnection

About The Project

MySQL Connector Python is used to access MySQL databases from Python using this repo.
Student databases will be utilized in this project.

Features

main.py program will be able to

Insert Book
Insert Student
Insert Borrowing

Step 1 : Run studentDb.sql file in command prompt.
studentDb.sql

How to Run MySQL

  mysql -u root -p

Give the path of .sql file as:

  mysql> source <sql Path.sql>

Step 2: Run main.py file
main.py

from secrets import choice
from tkinter import W
import mysql.connector as c # import the mysql connector
con = c.connect(host="localhost", user="root", password="root", database="studentdatabase") # connect to the database

print('*'*50)
print("Welcome to the Student Database")
print('*'*50)

cursor = con.cursor() # create a cursor
while True:
    choice= int(input("1-> Insert Book\n2-> Insert Student\n3-> insert Borrowing\n4-> Exit\n Your Choice: "))
    if choice == 1:
        book_name = input("Enter the book name: ")
        author = input("Enter the author name: ")
        isbn = input("Enter the isbn number: ")
        query = "INSERT INTO books (book_name, author_name, isbn_number) VALUES (%s, %s, %s)"
        values = (book_name, author, isbn)
        cursor = con.cursor()
        cursor.execute(query, values)
        con.commit()
        print("Book inserted successfully")
    elif choice == 2:
        name = input("Enter the name: ")
        roll = input("Enter the roll number: ")
        query = "INSERT INTO students (student_name, roll_number) VALUES (%s, %s)"
        values = (name, roll)
        cursor = con.cursor()
        cursor.execute(query, values)
        con.commit()
        print("Student inserted successfully")
    elif choice == 3:
        roll = input("Enter the roll number: ")
        book_name = input("Enter the book name: ")
        query = "INSERT INTO borrowings (roll_number, book_name) VALUES (%s, %s)"
        values = (roll, book_name)
        cursor = con.cursor()
        cursor.execute(query, values)
        con.commit()
        print("Borrowing inserted successfully")
    elif choice == 4:
        break
    else:
        print("Invalid choice") 
cursor.close()
con.close()
print("Connection closed")