# How to Match Regex in Flows
In **Flows**, you can validate string patterns using **regex** (regular expressions), but through **JSONata expressions**, not directly in conditionals.
This guide walks you through how to use regex in a **Set Variable** step using a JSONata expression, test it, and use the result in a follow-up **conditional** step.
### **Step-by-Step: Matching Regex in Flows**
#### **Step 1: Add a Set Variable Step**
1. In your flow, click **Add Step** and choose **Set variables**.
2. Add a new variable. Name it appropriately (e.g., phone\_regex).
#### **Step 2: Select the Input Variable to Evaluate**
1. In the **Set Variable** step, select the value as an variable which points to the actual input value you are validating.
2. Then, click to **select the variable** that holds the input you want to test.\
3. A modal will open with all the possibile variable modifiers available to you. Select the edit JSONata expression.\
#### **Step 3: Use a JSONata Expression for Regex**
In the JSONata editor modal, paste your expression. For example, to validate a phone number:
**$boolean($match($, /^(?:\\+?\[0-9] ?){6,14}\[0-9]$/))**
\
This expression checks if the input:
* Is made up of 6 to 14 digits
* May begin with a +
* Allows optional spaces
* Last digit is not a space
Then click **Save**.
#### **Step 4: Test Your Expression**
1. Click **Run test** in the Set Variable step.
2. Check the output section:
* If it matches, you’ll see: "phone\_regex": true
* If it doesn’t match, you'll see: "phone\_regex": false
#### **Step 5: Use the Output in a Conditional Step**
Now that your regex match is stored in a boolean variable (e.g., phone\_regex), you can use this in a **Conditional** step to control the flow.
For example:
* **If phone\_regex is true** → Proceed to success path
* **If phone\_regex is false** → Handle invalid input
### **Example Use Cases with JSONata Expressions**
#### **1. Email Validation**
#### $boolean($match($, /^\[\w-\\.]+@(\[\w-]+\\.)+\[\w-]{2,4}$/))
Use this to ensure an email format is valid.
#### **2. Zip Code Check (U.S.)**
$boolean($match($, /^\d{5}(-\d{4})?$/))
Matches 12345 or 12345-6789.
#### **3. Alphanumeric Code**
$boolean($match($, /^\[A-Za-z0-9]+$/))
Validates a string that must contain only letters and numbers.
#### **Starts with a Specific Prefix**
$boolean($match($, /^ABC/))
Returns true if the string starts with ABC.
