How to get full std::process::Command invocation as string in Rust? - rust

Question

So I want to execute a command over ssh using ssh2::channel but that crate takes command as &str. I was up until now constructing a std::process::Command and then I would format!("{:?}", cmd) but it doesn't output the env variables I have set.
To be more precise, I have this:
pub fn execute_command(
address: &String,
username: &str,
command: &Command,
buf: Option<&Vec<u8>>,
) -> anyhow::Result<Vec<u8>> {
let tcp = TcpStream::connect(address)?;
let mut sess = Session::new()?;
sess.set_tcp_stream(tcp);
sess.handshake()?;
sess.userauth_agent(&username)?;
let mut channel = sess.channel_session()?;
let command = format!("{:?}", command);
trace!("channel acquired for {}", address);
channel.exec(&command)?;
}
The problem is that Command doesn't include set env variables when being printed out via Debug. Is there another way to extract it as string for invocation where env variables would be included?

Answer 1

There's no built-in method on Command to do that. You could write a function to make such a string though:
fn pretty_cmd(cmd: &Command) -> String {
format!(
"{} {:?}",
cmd.get_envs()
.map(|(key, val)| format!("{:?}={:?}", key, val))
.fold(String::new(), |a, b| a + &b),
cmd
)
}
println!("{}", pretty_cmd(&cmd)); // e.g. "PATH"=Some("/usr") "sh" "-c" "echo hello"
Alternatively you could use a wrapper struct and implement Debug on that:
use std::fmt;
struct PrettyCmd(pub Command);
impl fmt::Debug for PrettyCmd {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(
f,
"{} {:?}",
self.0.get_envs()
.map(|(key, val)| format!("{:?}={:?}", key, val))
.fold(String::new(), |a, b| a + &b),
self.0
)
}
}
println!("{:?}", PrettyCmd(cmd)); // "PATH"=Some("/usr") "sh" "-c" "echo hello"
(try on playground)
The advantage of using a wrapper struct like this is that you can store a PrettyCmd wherever you currently store a Command, and the different Debug formatting will happen without needing an extra function call.