Regular expressions (regex) are a sequence of characters that define a pattern. They are used to find and match similar patterns in a piece of text. In other words, regex is a set of strings that holds a particular pattern. It is commonly used to authenticate values entered by the users during submission of any form. It helps:

• Increase efficiency: Regex makes it easier to find specific patterns in a large amount of data.
• Improve data identification: Regex allows to specify the exact pattern reducing the possibility of missing or misidentification of data.
• Facilitate reusability: Once you have created a regex pattern, you can reuse the same pattern in different contexts.
• Maintain data accuracy: Regex can be used to validate the input data and ensure that it meets certain criteria before processing it further.

Some common instances where regex can be useful in validating user's input: 

1. Email addresses: Regex can be used to validate the format of an email address. For example, the below regex pattern can be used to validate if an email address has the "@" symbol and the domain name in the right sequence. 
   ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
   
   
2. Account numbers: Regex can be used to validate bank account numbers. Here's an example of a regex pattern to validate a U.S. bank account number:
   ^\d{1,17}$
   The above pattern will check whether the account numbers contain 1-17 digits.
   
   
3. Password Strength: Regex can also be used to validate the strength of passwords. For example, the following regex pattern can be used to check for a strong password:
   ^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[^\w\d\s:])([^\s]){8,16}$
   This regex pattern checks for a password that contains at least one digit, one lowercase letter, one uppercase letter, one special character, and is between 8 and 16 characters long.

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Regex Gallery 

In addition to creating regex pattern while defining a criteria in layout/validation rules, there's also an option to select preferred regex patterns from the regex gallery. With regex gallery, you can use the predefined regex patterns at any time, eliminating the need to create the pattern every time.

Following are the Regex patterns that are available in the gallery:

Regex Criteria 

Regex criteria are special patterns that match the user input precisely. This regex criteria is used to find, validate, or replace specific patterns of characters in a chunk of text. Before looking into regex in layout and validation rules, let's cover the different regex criteria available.

1. Matches Regex:
   
   
1. When to use: This option is used when a user want to find data that precisely match a specific pattern defined using regex.
   
2. What can be achieved: Matches Regex can be used to search for data that adhere to a very specific and defined pattern. For example, you could use it to find if all email addresses matches a particular alphanumeric pattern.
   
   
2. Not Matches Regex:
   
   
1. When to use: Not Matches Regex is helpful when a user wants to filter out data that match a particular regex pattern.
   
2. What can be achieved: This option excludes data that meet a specific pattern. For instance, you might want to exclude usernames entries that contain special characters. By applying Not Matches Regex, you can easily avoid the usernames that don't align with your desired pattern.
   
   
3. Contains Regex:
   

1. When to use: The Contains Regex option is used when a user wants to find or validate data that contain a specific pattern.
   
2. What Can Be Achieved: This option allows user to identify instances where a particular pattern exists within the provided text. Consider an online marketplace where sellers list products. To ensure accurate shipping information, you want to identify product listings that mention U.S. postal codes. By using Contains Regex, you can automatically detect listings that reference the five-digit format of U.S. postal codes. 

Points to Remember

• A layout/validation rule can have five primary conditions, and each condition can have a separate regex criteria.
• You cannot add the regex criteria for secondary conditions in layout and validation rule.
  
  
  
  
  
  
• While defining the regex criteria, you can either manually create a custom regex pattern or select a pattern from the regex gallery.
  
  
  

Using  Regex in layout rules 

Layout rules are used to define dependency between fields or sections based on the user's input. So, when a user fills in a field, the layout progressively adds more fields or sections based on the user's input. In general, layout rules can be used to define the dynamic behavior of the layout based on a value entered in a field. See also: Creating Layout Rules in Zoho Desk.

While configuring layout rules, regex can be set on the primary field so that the value can be validated when entered by the user. This can be useful in determining the layout behavior based on the format of the data given and eliminates the need to create several criteria. 

For example, in a product purchase form a user needs to fill the credit card number, based on which a section with fields such as expiry date, card holder's name etc. is displayed. With regex, the credit card number format and pattern can be validated so that users fill a valid 16-digit number. If the field value is incorrect, the dependent section will not be displayed. 

You can create a layout rule using the below regex criteria:
Credit card number + Contains Regex + Credit Card Number

 To create a layout rule using regex 

1. Navigate to Setup (  ) > Customization > Layout and Fields.
2. Select Layout Rules from the left pane.
3. Click Create Rule in the upper-right corners.
   
   
   
   
4. In the Create Layout Rule window, do the following:
   
1. Enter the rule name.
   
2. Give a Description for the rule.
   
3. Select the desired Layout.
   
4. Choose a Primary field that controls this rule.
   
5. Choose a Condition to initiate the rule. 
   
6. Select the desired regex criteria. 
   
7. You can choose from Matches Regex, Not Matches Regex, and Contains Regex (For example: Credit card Number + Contains Regex + Credit Card Number).
   
8. Click Next.
   
   
   
   
5. In the Create Layout Rule Editor, click Trigger an action and choose the desired actions from the list.
6. In the Create Action page, click Show Fields, Show Sections, and Set Mandatory Fields, then select the respective fields.
7.  Click Done.
   Actions in Layout Rule.
8. Check Apply to Help Center to manage dependencies between fields when tickets are submitted through your help center.
9. Click Save.
   
   
   
   

Using Regex in validation rules 

Using regex in validation rules, helps ensure that only those records where the user's input matches the specific pattern are saved in the system. This was, organizations can prevent invalid inputs.

For example, let's say you want to validate whether an end user enters an email address in a specific format, such as johnsmith123@zylker.com. In such a case, you can create a validation rule and define or choose a regex pattern that matches the format of a valid email address (Such as Email + Matches Regex + Email Address). This pattern can then be used to check whether the entered email address matches that format. 

Likewise, you can also create a regex pattern that matches email addresses ending with the zylker [your desired] domain. 

(?i)[a-z0-9.-]+@zylker\.com$

In this pattern, (?i) is a modifier that makes the pattern case-insensitive. This regular expression allows for alphanumeric characters (lowercase), periods, and hyphens in the email username. It then matches the literal string "@zylker.com", and the $ symbol specifies that the match must end with the domain name "zylker.com".

 To create a validation rule using regex 

1. Navigate to Setup (  ) > Customization > Layout and Fields.
2. Select Validation Rules from the left pane.
3. Click Create Rule in the upper-right area
   
   
   
   
4. In the New Validation Rule window, do the following:
   
1. Select the desired Layout.
   
2. Choose a primary field that controls this rule.
3. Click Next.
5. In the Create Validation Rule editor, click Add Another Option and specify the regex criteria to validate.
   You can choose from Matches Regex, Not Matches Regex, and Contains Regex. For example: Email + Matches Regex + Email Address.
6. Click Done.
   
   
   
   
   
   
7. Specify the necessary Alert message.
   
   
   
   
8. Check Apply to Help Center to validate tickets submitted through your help center.
9. Click Save.

Note: You can either disable or delete the layout or validation rule when not in use. When you delete a rule, it will be permanently removed and cannot be recovered.

See more: Deleting Layout Rules and Deleting Validation Rules.