[Rust] Stage #JV1 stuck on error where cat doesn't find a file the test expects to be there

I’m stuck on Stage #JV1

I’ve tried enabling debug output, but it made no change in my logs.

Here are my logs:

[compile]    Compiling codecrafters-shell v0.1.0 (/app)
[compile]     Finished `release` profile [optimized] target(s) in 0.83s
[compile] Moved ./.codecrafters/run.sh → ./your_program.sh
[compile] Compilation successful.
[tester::#JV1] Running tests for Stage #JV1 (Redirection - Redirect stdout)
[tester::#JV1] [setup] export PATH=/tmp/mango/pear/orange:$PATH
[tester::#JV1] Running ./your_program.sh
[tester::#JV1] [setup] echo "banana" > "/tmp/rat/banana"
[tester::#JV1] [setup] echo "grape" > "/tmp/rat/grape"
[tester::#JV1] [setup] echo "pear" > "/tmp/rat/pear"
[your-program] $ ls -1 /tmp/rat > /tmp/pig/bee.md
[your-program] $ cat /tmp/pig/bee.md
[your-program] banana
[your-program] grape
[your-program] pear
[tester::#JV1] ✓ Received redirected file content
[your-program] $ echo 'Hello Maria' 1> /tmp/pig/dog.md
[your-program] $ cat /tmp/pig/dog.md
[your-program] Hello Maria
[tester::#JV1] ✓ Received redirected file content
[your-program] $ cat /tmp/rat/grape nonexistent 1> /tmp/pig/rat.md
[your-program] cat: nonexistent: No such file or directory
[tester::#JV1] ✓ Received error message
[your-program] $ cat /tmp/pig/rat.md
[your-program] cat: /tmp/pig/rat.md: No such file or directory
[tester::#JV1] ^ Line does not match expected value.
[tester::#JV1] Expected: "grape"
[tester::#JV1] Received: "cat: /tmp/pig/rat.md: No such file or directory"
[your-program] $ 
[tester::#JV1] Assertion failed.
[tester::#JV1] Test failed

I don’t quite understand how this error happens, as the error seems to be from cat, not my code. For some reason cat returns an error that says it can’t find the file or directory, but the test expects there to be a file there.

Preceding tests shows cat working fine and printing the expected contents when there is a file (tmp/pig/bee and tmp/pig/dog), so why the /tmp/pig/rat.md call to cat fails to find a file when the test expects it to find one is a mystery to me.

I’ve no idea how my code can be responsible for cat sometimes, but not always, failing to find a file that exists. If it wasn’t for how unlikely it is, I’d honestly conclude that it’s the test that’s set up wrong, erroneously trying to access and print the contents of a file that doesn’t exist. But I assume that’s not the case, and that there’s some part of my code that’s messing up.

Here’s the code that should be relevant to the output of my logs:

// This is the code in charge of running the program and passing on its output
// The function this code exists in returns a Resul<String, String>
// It returns OK with parsed output when the program runs and outputs parseable text
// It returns Err with appropriate message if program fails to run, outputs to stderr or the parsing of output fails
if let Ok(output) = process::Command::new(cmd).args(args).output() {
    if output.status.success() {
        match str::from_utf8(&output.stdout) {
            Ok(val) => result = Ok(val.trim().to_string()),
            Err(_) => result = Err(String::from("failed to parse program output as text"))
        }
    } else {
        match str::from_utf8(&output.stderr) {
            Ok(val) => result = Err(val.trim().to_string()),
            Err(_) => result = Err(String::from("failed to parse program output as text"))
        }
    }
} else {
    let err_message = String::from("couldn't execute program");
    result = Err(err_message)
}

// Later in the main loop this code handles results sent from the various functions associated with the shells different commands
// It prints to stderr if the result returned an error message
// It writes to file if the result returned an OK and the user initially gave arguments to pipe output to a file
// It prints to stdout if the result returned OK with a non-empty string and the user didn't try to pipe to a file
match result {
    Ok(message) => {
        if !output_file_path.is_empty() {
            write_output_to_file(message, output_file_path);
        } else if !message.is_empty() {
            println!("{message}");
        }
    }
    Err(message) => {
        eprintln!("{message}");
    }
}

Hey @MarsAstro, could you upload your code to GitHub and share the link? It will be much easier to debug if I can run it directly.

Sure thing, here you go!

Glancing at your code you only write upon success? So you run cat /tmp/rat/grape nonexistent 1> /tmp/pig/rat.md and it finishes with non-zero exit code because of nonexistent. But cat still writes output which is supposed to go /tmp/pig/rat.md even if empty or not.

My guess is you don’t forward data directly, but instead capture it and wait. So I guess the output.status.success is false and but match str::from_utf8(&output.stderr) is true if I had to guess. Later at the end you match result with Err(message) you write (forward) the stderr from cat which is cat: nonexistent: No such file or directory and is correct; the tester expected that output from that command. But you never forwarded the stdout from cat to the file. Thus the next step fails because the file indeed does not exist, but it was supposed to.

Aah, right! Yes, I’ve been operating under the assumption that cat only outputs if all its arguments are valid, but if it outputs for each argument separately then that would explain the error here.

I think you’ve nailed it! I’ll try a rewrite later to see if that fixes it. Do you know of any ways to use cat on windows so I can test it locally? Or better yet, if there’s a way to get a unix style terminal in VSCode on windows

EDIT: Nvm, figured out the unix thing. I set VScode to use Git Bash. Now I can test cat locally!

I never bothered anymore with MinGW or cygwin since 10 years ago. If you installed Git via an “extended” installation like “Git for Windows”, then you might have “Git Bash” which is a Bash and mine finds cat.

But the more recent solutions is to run Linux inside WSL, can’t remember but something like wsl -d Ubuntu.

Thanks! I could indeed do that, I figured it out myself right after I asked the question. Cat works locally now, and I can see it does indeed output each argument separately, so the issue is almost certainly what you said.

But also, a bit of advice. You are trying to be too clever, you shouldn’t write to stdout or stderr unless is a direct decision by your shell. If you are switching based on exit code, your shell already did its job of launching the process. Just let stdout and stderr end up wherever the user/program wanted it to, which by default, in the absence of redirects, pipes, etc., should be your shell’s stdout and stderr.