List of Most Common Regular Expressions and Their Uses

Introduction

A regular expression is a pattern that could be matched against an input text. The following is the important list of regular expressions that we use widely in our applications.

1. Email id validation
2. URL validation
3. Password strength validation
4. Mobile number validation
5. String pattern validation

For using a regular expression in C# server side, we need to use the following namespace.

using System.Text.RegularExpressions;

Remember to remove / at the start and the end of the string to convert a JavaScript Regex to C#.

1. Email id validation regular expression

Regular expression:

1. /^\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$/ (Email Id)
2. /^([\w-\.]+@(?!gmail.com)(?!yahoo.com)(?!hotmail.com)([\w- ]+\.)+[\w-]{2,4})?$/ (free/domain specific email id)

2. URL validation regular expression

Regular expression:

1. /(http(s)?://)?([\w-]+\.)+[\w-]+[.com]+(/[/?%&=]*)?/ (with or without http)
   
   
2. /((www\.|(http|https|ftp|news|file)+\:\/\/)[_.a-z0-9-]+\.[a-z0-9\/_:@=.+?,##%&~-]*[^.|\'|\# |!|\(|?|,| |>|<|;|\)])/( valid everywhere)

3. Password strength validation regular expression

Regular expression:

1. / ^[a-z0-9\.@#\$%&]+$/ (only contains letter [a-z] digits[0-9], special characters(@#$%&))
   
   
2. / ^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$/ (Minimum 8 characters at least 1 Alphabet and 1 Number)
   
   
3. / ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[$@$!%*?&])[A-Za-z\d$@$!%*?&]{8,}/ (Minimum 8 characters at least 1 Uppercase Alphabet, 1 Lowercase Alphabet, 1 Number and 1 Special Character)
   
   
4. / ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[$@$!%*?&])[A-Za-z\d$@$!%*?&]{8,10}/ (Minimum 8 and Maximum 10 characters at least 1 Uppercase Alphabet, 1 Lowercase Alphabet, 1 Number and 1 Special Character)
   
   
5. / ^[a-zA-Z0-9\s]{7,16}$/ (Minimum length 7 and Maximum length 16 Characters allowed [a–z] [A-Z] [0-9])

4. Mobile number validation regular expression

Regular expression:

1. / ^((\+){0,1}91(\s){0,1}(\-){0,1}(\s){0,1}){0,1}9[0-9](\s){0,1}(\-){0,1}(\s){0,1}[1-9]{1}[0-9]{7}$/ (without +91 or 0)
   
   
2. /^((\\+91-?)|0)?[0-9]{10}$/ (with or without +91 or 0)
   
   
3. ^((\\+|00)(\\d{1,3})[\\s-]?)?(\\d{10})$/ (split the number and the country code)

5. String pattern validation regular expression

Regular expression:

1. /(?s)^((?!manish).)*$/ (string contains manish)
2. \d/ (at list one digit )
3. /(.)*(\\d)(.)* / (contains number)
4. /^\d$/ (contains only number )
5. /^\d{11}$/ (contains only 11 digit number )
6. /^[a-zA-Z]+$/ (contains only letter )
7. /^[a-zA-Z0-9]+$/ (contains only letter and number )

Use of the regular expressions

Use the preceding regular expressions in the following ways.

In the following example, I am showing an email validation in various ways. Just replace the regular expression and use any of the others to use another validation.

Using JavaScript

Email Address

1. <asp:TextBox ID="txtemail" runat="server" ></asp:TextBox>
2. <asp:Label ID="lblmsg" runat="server" ></asp:Label>
3. <br/>
4. <asp:Button ID="btnsubmit" runat="server" Text="Submit"
5. onclick="btnsubmit_Click" />
C#

1. private bool validateEmailId(string emailId)
2. {
3. return Regex.IsMatch
4. (
5. emailId,
6. @"^\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*$",
7. RegexOptions.IgnoreCase
8. );
9. }
Call the preceding function in a button click.

1. protected void btnsubmit_Click(object sender, EventArgs e)
2. {
3. if (validateEmailId(txtemail.Text.Trim()))
4. {
5. lblmsg.Text = string.Empty;
6. }
7. else
8. {
9. lblmsg.Text = "Please provide a valid email address";
10. lblmsg.ForeColor = System.Drawing.Color.Red;
11. }
12. }