today in build scripts from my nightmares:

```rust
    let re = Regex::new(r"target = .*").unwrap();
    let config_toml = include_str!(".cargo/config.toml");
    let result = re.replace(config_toml, format!("target = \"{}\"", target));
    let mut f = File::create(".cargo/config.toml").unwrap();
    f.write_all(result.as_bytes()).unwrap();
```