clippy::suspicious_command_arg_space: single argument that looks like it should be multiple arguments

What you see

warning: single argument that looks like it should be multiple arguments
 --> main.rs:3:40
  |
3 | std::process::Command::new("echo").arg("-n hello").spawn().unwrap();
  |                                        ^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#suspicious_command_arg_space
  = note: `#[warn(clippy::suspicious_command_arg_space)]` on by default
help: consider splitting the argument
  |
3 - std::process::Command::new("echo").arg("-n hello").spawn().unwrap();
3 + std::process::Command::new("echo").args(["-n", "hello"]).spawn().unwrap();
  |

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

Command::arg() does not split arguments by space. An argument like arg("-t ext2") will be passed as a single argument to the command, which is likely not what was intended.

Code that is most likely wrong or useless. Warns by default.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

std::process::Command::new("echo").arg("-n hello").spawn().unwrap();

Write this instead

std::process::Command::new("echo").args(["-n", "hello"]).spawn().unwrap();

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

#[allow(clippy::suspicious_command_arg_space)]
fn my_function() { /* ... */ }

[lints.clippy]
suspicious_command_arg_space = "allow"

cargo clippy -- -A clippy::suspicious-command-arg-space

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.