I'm writing a test to execute sql, but the spawned command just can't find the created files!
The code below reproduces the error via cat command:
for simple case, it works: Rust Playground
but doesn't work for this: Rust Playground
I really don't know what's going on...
You are accidentally debug-escaping the format string in the .arg() of the Command. This works. (You probably confused shell-escaping with .arg()? Escaping doesn't happen here, you are literally passing the prepared arguments to the command, the shell has no say in it.)
Thanks! I never knew that, and I was always thinking about checking the existence of files.
Now the error from cat is clearer to me than that from clickhouse...
// clickhouse error:
stderr = Code: 107. DB::ErrnoException: Cannot open file "/tmp/.tmp7AJJ9D/1-xxx/__full.sql", errno: 2, strerror: No such file or directory. (FILE_DOESNT_EXIST)
// cat error:
stderr = cat: '"/tmp/.tmp7AJJ9D/1-xxx/__full.sql"': No such file or directory
So the error can be reproduced in the simple case: Rust Playground LOL
And I read the arg signature again
pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command
then we can directly pass the path into it 
let output = Command::new("cat").arg(full_path).output()?;