nya.rs 
nya is a small and cute file processor. It does only what you want it to do, and nothing else.
Installation
Install cargo-edit to extend Cargo, allowing you to add, remove, and upgrade dependencies by modifying your Cargo.toml file from the command line.
Usage
Currently, the way you'd use it is somewhat like this:
extern crate nya;
use ;
This reads all files from a directory, and replaces the content of the first one with "test hello". Further documentation can be found on docs.rs.
License
Licensed under the AGPL-3.0+. See LICENSE.