jsonpath substring

JSONPath does not have a built-in function for substring, but you can use a combination of other functions to achieve the same result.

For example, to extract a substring from a string value in a JSON object, you can use the `substring()` function along with the `match()` function.

Here's an example JSON object:

{
  "name": "John Doe",
  "email": "john.doe@example.com"
}

To extract the first name from the `name` field, you can use the following JSONPath expression:

$.name.match(/^[^ ]+/)

This expression uses the `match()` function with a regular expression pattern that matches the first word in the string (i.e., the first name).

You can also use the `substring()` function to extract a substring of a specific length from a string value. For example, to extract the first three characters of the `name` field, you can use the following expression:

$.name.substring(0, 3)

This expression uses the `substring()` function with a start index of 0 and a length of 3 to extract the first three characters of the string.