use std::{fs, io, io::prelude::*, path::PathBuf}; fn bash_program() -> io::Result<()> {    use std::io::IsTerminal;    if !std::io::stdout().is_terminal() {        eprintln!("warning: `bash-program` subcommand not meant for scripting, format may change");    }    println!("{}", gix_testtools::bash_program().display());    Ok(())} fn mess_in_the_middle(path: PathBuf) -> io::Result<()> {    let mut file = fs::OpenOptions::new().read(false).write(true).open(path)?;    file.seek(io::SeekFrom::Start(file.metadata()?.len() / 2))?;    file.write_all(b"hello")?;    Ok(())} #[cfg(unix)]fn umask() -> io::Result<()> {    println!("{:04o}", gix_testtools::umask());    Ok(())} fn main() -> Result<(), Box<dyn std::error::Error>> {    let mut args = std::env::args().skip(1);    let scmd = args.next().expect("sub command");    match &*scmd {        "bash-program" | "bp" => bash_program()?,        "mess-in-the-middle" => mess_in_the_middle(PathBuf::from(args.next().expect("path to file to mess with")))?,        #[cfg(unix)]        "umask" => umask()?,        _ => unreachable!("Unknown subcommand: {}", scmd),    }    Ok(())}