Regex what it is ?? How to decrept ??

Hi folks ,
For many times in programming tasks I have used regex patterns.
Every time I google and find expected regex pattern for my task, but though to write detail post so that next time I ‘ll not be blindly using regex in stackoverflow 😉

We gonna discuss below questions :
1) What is Regex?
2) where to use it??
3) how to write and read regex?
4) utilities available on web to write and read regex???

1) What is Regex??
It stands for Regular expressions, its pattern which describes certain text.
It’s way to describe a different series of text in short expression.
Different languages, technologies has different implementation of regex, your regex which is working in PHP may not work in java.
As I work majorly in JAVA technologies I ‘ll focus on JAVA regex patterns.

2) where to use it???
Many places let me give you some examples,
1. do you want to search email address in 1000 lines of text ?? use regex.
2. Do you want to search specific file pattern to pass your condition ? use regex..
3. Do you want to check if password meets certain criteria ?? like mix of uppercase and lowercase? use regex.

3) how to write and read regex?

Regex definition is defined under 3 sections :
1. Common Matching Symbols
2. Meta characters
3. Quantifiers.

The best explanations with examples i found here :

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