The Regex block

The Regex block is deprecated and isn't available in Postman Flows. To use a regular expression for processing data, include the regex in your TypeScript or FQL code in an Evaluate block.

Using a regex in an Evaluate block can be a powerful approach. Here's an example:

• Suppose you have a JSON array of objects that describe auto service invoices. From these invoices, you want to extract the line items for brake hardware - that is, anything to do with brakes that’s not brake fluid.

• In your Evaluate block's TypeScript expression, a plain .includes ("brake") isn't enough, because it still matches the string "brake fluid" that you want to exclude.

• Instead, you can use a regex that matches strings that contain the word "brake" but only if they're not followed by the word "fluid". You can do this with a negative lookahead - (?! fluid) in this case - to exclude items that contain the unwanted string.

If you name the Evaluate block's input variable invoices, the whole TypeScript expression might look like this:

regex = /\bbrake(?! fluid)\b/i;

invoices.flatMap(inv =>
  inv.line_items.filter(item => regex.test(item.description))
);

The TypeScript expression filters and maps the JSON input, using the regex to extract only the desired items. The complete flow shows how this looks: