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# How to Write / Formulation Regex

Articles on: [Workflows & Activities](/en/category/workflows-activities-169b7fg/)

Regex formula is primarily used for pattern matching within strings (such as search, replace, or validation tasks). Regular expressions are commonly used in programming and text processing.

Regex is a regular expression that defines or restricts what a user inputs/fill on the input questions (Input text, Integer, decimal, etc.).

It is a sequence of characters that define a search pattern.

We have a provision to use it both in the list and in the workflows, see below on how to formulate one.   
  
*   Characters definition;
  
*   [] - A set of characters
  
*   \ - Signals a special sequence (can also be used to escape special characters)
  
*   . - Any character (except newline character)
  
*   ^ - Starts with
  
*   $ - Ends with
  
*   {} - Exactly the specified number of occurrences
  
*   | - Either or - Used to easily combine regex with two or more functions
  
*   () - Capture and group
  
  
*   Sets descriptions;
  
*   [0123] - Returns a match where any of the specified digits (0, 1, 2, or 3) are present
  
*   [0-9] - Returns a match for any digit between 0 and 9
  
*   [0-5][0-9] - Returns a match for any two-digit numbers from 00 and 59
  
  
Examples  
  
*   ^([1-9]|1[012])$
 
*   ^ -  Anchors the regex at the start of the string
  
*   [1-9] - Matches 1 to 9
  
*   | - Basically used when you want to combine two or more regex - alternation matches the previous match or the following match.
  
*   1[012] - Matches 10, 11, or 12
  
*   $ - Anchors the regex at the end of the string.
  
  
*   ^2[0-9]{10}$ - Allows 10 Digits starting with a 2.
  
*   ^[0]{1}[1-9]{1}[0-9]{8}$ - Values need to have at least 10 digits starting with a 0
  
*   ^237[0-9]{9}$ - Values need to have at least 12 digits starting with 237
  
The best site to use in formulating Regex and testing them is [Regex101](https://regex101.com/), Please do test these Regex first before implementing them on the workflows/list.