$regsub

$regsub([name], text, re, subtext, %var)

Performs a regular expression match, like $regex(), and then performs a substitution using subtext.
Returns N, the number of substitutions made, and assigns the result to %var.

Example:

alias testing {
 var %num_of_matches = $regsub(a dog was eating milk,/dog/g,cat,%new_content)
 ;%num_of_matches will have a value of 1, since 'dog' was mathced once
 ;%new_content will be 'a cat was eating milk'
}