Getting started with Regular Expression/REGEX

Pronounced as Regex or rejex?

probably is the most dificult thing to answer, But i will go with Regex as it stands for Reguar Expression

Why use Regex?

Validate Text
Search through text

builtin functions in js to write regex

match() - search for a matching patern
replace() - replace that maching patterns

Regex strings starts and ends with / and if there is extra information needed, we can use regex flags after the ending / like this //g the g here is a flag

Special Regex Characters

These are all the Special characters.

.^&*+-?()[]{}\|

| logical OR
() Grouping
quantifiers
```
`?` - 0 or 1 times

`*` - 0 or multiple times

`+` - 1 or multiple times
```
by adding braces {} we can give them explicit count.
?r{2,6}
\ escape a special characters
\d to escape digits
\w to escape words
\D to escape neither digits nor words
[] Ranging
^ Negation, do the opposite

Flags

are written at the right side of the / like so //g The g flat turns it into a global, which will make it search for multiple matches

visit regexr.com for more. it has amazing cheatsheet and traning area.

\[ \begin{aligned} KL(\hat{y} || y) &= \sum_{c=1}^{M}\hat{y}_c \log{\frac{\hat{y}_c}{y_c}} \\ JS(\hat{y} || y) &= \frac{1}{2}(KL(y||\frac{y+\hat{y}}{2}) + KL(\hat{y}||\frac{y+\hat{y}}{2})) Let's begin with a eulers formula, $e^{i\pi + 1} = 0$. \end{aligned} \]

This is an inline $a^*=x-b^*$ equation.

These are block equations:

\[a^*=x-b^*\] \[ a^*=x-b^* \] \[ a^*=x-b^* \]

These are block equations using alternate delimiters:

$$a^*=x-b^*$$ $$ a^*=x-b^* $$ $$ a^*=x-b^* $$