Regex for unique email validation-CodePudding

My issue is finding a Regex that matches the following rules.

The main Regex I'm using to check if the email is valid is /^\w ([.-]?\w )*@\w ([.-]?\w )*(\.\w{2,3}) $/

I would like to use 3 additional Regexs to match:

characters AND @ (nothing after @)
@ domain OR @ domain top-level-domain
characters AND NO @

These 3 Regexs should be sufficient to check if:

A domain hasn't been entered
A username hasn't been entered
If the @ sign hasn't been entered

If the input doesn't match these rules then they will receive a generic error message.

CodePudding user response：

Using Regex101.com I was able to create my own regular expressions and use their explanations to understand them. I am using 8 Regexs for this email input:

/^\w ([.-]?\w )*@$/;
/^\w ([.-]?\w )*$/;
/^\w ([.-]?\w )*(\.) $/;
/^@\w ([.-]?\w )*$/;
/^@\w ([.-]?\w )*(\.)$/;
/^@\w ([.-]?\w )*(\.\w{2,3}) $/;
/^\w ([.-]?\w )*(\.\w{2,3}) $/;
/^\w ([.-]?\w )*@\w ([.-]?\w )*(\.\w{2,3}) $/;

Using these expressions and one test against whether the input is empty, I display the following messages:

Enter your email address
Don't forget to include '@'.
Enter a domain after '@'.
Enter a username before the '@'.
This email address is not valid.

CodePudding user response：

This is a valid email address using reg expression:

[\w\d._] @[\w\d] \.[\w]{2,3}

All what you need to do is to create a condition statement against the above string. If it matches, then it's a valid email address, otherwise it's a non valid address.

Below is a Python example (which you can still modify to match whatever language you want):

import re

pattern = "^[a-zA-Z0-9] @[a-zA-Z0-9] \.[a-zA-Z]{2,3}$"

user_input = input()

if(re.search(pattern, user_input)):
    print("This is a valid email")

else:
    print("This isn't a valid email")