(string-replace-substring str searchstr replacestr)

string-replace-substring replaces searchstr with replacestr throughout a string.

Parameter	Description
str	Input string
searchstr	The string searched for
replacestr	The string to replace with

Example

Example 1: Replace the substring "brown fox" with a "dinosaur".

> (define a "The quick brown fox jumps over the lazy dog.")
> (string-replace-substring a "brown fox" "dinosaur")
"The quick dinosaur jumps over the lazy dog."