Question

I’m always confused with Regex format how they work and how to make Regex according to my requirement. I just copy some common Regex formats and paste in my project but obviously we cant find every Regex format according to our requirement. So i would like to learn about Regex.

I make it just from my guess after run code again and again but still i dont know so much about this Regex

NSString *regexNumber = @"[123456789][0-9]{0}([0-9]{1})?";

This compare Age, according to this age should be start from 1-9, minimum 1 digit, maximum 2 digits and numeric only.

Now i want to make Regex for Name – (exp – vakul, Vakul, vakul saini, Vakul Saini, vakul Saini, Vakul saini etc.), Email, Phone Number, String Only, Birthday, URL.
But dont want to copy and paste i want to learn how they work and how to make my own Regex.

Answer 1

A regular expression is a text pattern consisting of a combination of alphanumeric characters and special characters known as metacharacters

The metacharacters are:

\ | ( ) [ { ^ $ * + ? . < >

. —- It is instead a special metacharacter which matches any character.

* —- The * character matches zero or more occurrences of the character in a row.

+ —- The + character is similar to * but matches one or more.

? —- Zero or one instance of characters

{m,n} —- means match m or up to n characters. eg {1,5} matches 1 or upto 5 characters

^ —- it would match any line which began with the word following it

$ — it would match any line which ends with the word following it

<> — matches words between them. Eg. returns all words that contain abc

You can form groups, or subexpressions as they are frequently called, by using the begin and end parenthesis characters:
() The ( starts the subexpression and the ) ends it

| — Or Parameter

[ and ] — Sequence of characters. Any characters put inside the sequence brackets are treated as literal characters, even metacharacters. The only special characters are – which denotes character ranges, and ^ which is used to negate a sequence. eg. [a-z]

This is the most basic knowledge you need for regular expressions and they are same for almost all languages.

For further details you can refer this link