How can I capture the result of var_dump to a string?

I’d like to capture the output of var_dump to a string.

The PHP documentation says;

As with anything that outputs its result directly to the browser, the output-control functions can be used to capture the output of this function, and save it in a string (for example).

What would be an example of how that might work?

print_r() isn’t a valid possibility, because it’s not going to give me the information that I need.