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#2 in #command-name

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Fun Run

What does the "Zombie Zoom 5K", the "Wibbly wobbly log jog", and the "Turkey Trot" have in common? They're runs with a fun name! That's exactly what fun_run does. It makes running your Rust Commands more fun, by naming them.

What is Fun Run?

Fun run is designed for the use case where not only do you want to run a Command you want to output what you're running and what happened. Building a CLI tool is a great use case. Another is creating a buildpack.

Here's some things you can do with fun_run:

  • Advertise the command being run before execution
  • Customize how commands are displayed
  • Return error messages with the command name.
  • Turn non-zero status results into an error
  • Embed stdout and stderr into errors (when not streamed)
  • Store stdout and stderr for debug and diagnosis without displaying them (when streamed)

Just like you don't need to dress up in a giant turkey costume to run a 5K you also don't need fun_run to do these things. Though, unlike the turkey costume, using fun_run will also make the experience easier.

Ready to Roll

For a quick and easy fun run you can use the fun_run::CommandWithName trait extension to stream output:

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("bundle");
cmd.args(["install"]);

// Advertise the command being run before execution
println!("Running `{name}`", name = cmd.name());

// Stream output to the end user
// Turn non-zero status results into an error
let result = cmd
    .stream_output(std::io::stdout(), std::io::stderr());

// Command name is persisted on success or failure
match result {
    Ok(output) => {
        assert_eq!("bundle install", &output.name())
    },
    Err(cmd_error) => {
        assert_eq!("bundle install", &cmd_error.name())
    }
}

Pretty (good) errors

Fun run comes with nice errors by default:

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("becho");
cmd.args(["hello", "world"]);

match cmd.stream_output(std::io::stdout(), std::io::stderr()) {
    Ok(_) => todo!(),
    Err(cmd_error) => {
        let expected = r#"Could not run command `becho hello world`. No such file or directory"#;
        let actual = cmd_error.to_string();
        assert!(actual.contains(expected), "Expected {actual:?} to contain {expected:?}, but it did not")
    }
}

And commands that don't return an exit code 0 return an Err so you don't accidentally ignore a failure, and the output of the command is captured:

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("bash");
cmd.arg("-c");
cmd.arg("echo -n 'hello world' && exit 1");

// Quietly gets output
match cmd.named_output() {
    Ok(_) => todo!(),
    Err(cmd_error) => {
        let expected = r#"
Command failed `bash -c "echo -n 'hello world' && exit 1"`
exit status: 1
stdout: hello world
stderr: <empty>
        "#;

        let actual = cmd_error.to_string();
        assert!(
            actual.trim().contains(expected.trim()),
            "Expected {:?} to contain {:?}, but it did not", actual.trim(), expected.trim()
        )
    }
}

By default, streamed output won't duplicated in error messages (but is still there if you want to inspect it in your program):

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("bash");
cmd.arg("-c");
cmd.arg("echo -n 'hello world' && exit 1");

// Quietly gets output
match cmd.stream_output(std::io::stdout(), std::io::stderr()) {
    Ok(_) => todo!(),
    Err(cmd_error) => {
        let expected = r#"
Command failed `bash -c "echo -n 'hello world' && exit 1"`
exit status: 1
stdout: <see above>
stderr: <see above>
        "#;
        let actual = cmd_error.to_string();
        assert!(
            actual.trim().contains(expected.trim()),
            "Expected {:?} to contain {:?}, but it did not", actual.trim(), expected.trim()
        );

        let named_output: fun_run::NamedOutput = cmd_error.into();

        assert_eq!(
            "hello world",
            named_output.stdout_lossy().trim()
        );

        assert_eq!(
            "bash -c \"echo -n 'hello world' && exit 1\"",
            named_output.name()
        );
    }
}

Renaming

If you need to provide an alternate display for your command you can rename it, this is useful for omitting implementation details.

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("bash");
cmd.arg("-c");
cmd.arg("echo -n 'hello world' && exit 1");

let mut renamed_cmd = cmd.named("echo 'hello world'");

assert_eq!("echo 'hello world'", &renamed_cmd.name());

This is also useful for adding additional information, such as environment variables:

use fun_run::CommandWithName;
use std::process::Command;


let mut cmd = Command::new("bundle");
cmd.arg("install");

let env_vars = std::env::vars();
# let mut env_vars = std::collections::HashMap::<String, String>::new();
# env_vars.insert("RAILS_ENV".to_string(), "production".to_string());

let mut renamed_cmd = cmd.named_fn(|cmd| fun_run::display_with_env_keys(cmd, env_vars, ["RAILS_ENV"]));

assert_eq!(r#"RAILS_ENV="production" bundle install"#, renamed_cmd.name())

Debugging system failures with which_problem

When a command execution returns an Err due to a system error (and not because the program it executed launched but returned non-zero status), it's usually because the executable couldn't be found, or if it was found, it couldn't be launched, for example due to a permissions error. The which_problem crate is designed to add debuggin errors to help you identify why the command couldn't be launched.

The name which_problem works like which to but helps you identify common mistakes such as typos:

$ cargo whichp zuby
Program "zuby" not found

Info: No other executables with the same name are found on the PATH

Info: These executables have the closest spelling to "zuby" but did not match:
      "hub", "ruby", "subl"

Fun run supports which_problem integration through the which_problem feature. In your Cargo.toml:

# Cargo.toml
fun_run = { version = <version.here>, features = ["which_problem"] }

And annotate errors:

use fun_run::CommandWithName;
use std::process::Command;

let mut cmd = Command::new("becho");
cmd.args(["hello", "world"]);

#[cfg(feature = "which_problem")]
cmd.stream_output(std::io::stdout(), std::io::stderr())
    .map_err(|error| fun_run::map_which_problem(error, cmd.mut_cmd(), std::env::var_os("PATH"))).unwrap();

Now if the system cannot find a becho program on your system the output will give you all the info you need to diagnose the underlying issue.

Note that which_problem integration is not enabled by default because it outputs information about the contents of your disk such as layout and file permissions.

What won't it do?

The fun_run library doesn't support executing a Command in ways that do not produce an Output, for example calling Command::spawn returns a Result<std::process::Child, std::io::Error> (Which doesn't contain an Output). If you want to run for fun in the background, spawn a thread and join it manually:

use fun_run::CommandWithName;
use std::process::Command;
use std::thread;


let mut cmd = Command::new("bundle");
cmd.args(["install"]);

// Advertise the command being run before execution
println!("Quietly Running `{name}` in the background", name = cmd.name());

let result = thread::spawn(move || {
    cmd.named_output()
}).join().unwrap();

// Command name is persisted on success or failure
match result {
    Ok(output) => {
        assert_eq!("bundle install", &output.name())
    },
    Err(cmd_error) => {
        assert_eq!("bundle install", &cmd_error.name())
    }
}

FUN(ctional)

If you don't want to use the trait, you can still use fun_run by functionally mapping the features you want:

let mut cmd = std::process::Command::new("bundle");
cmd.args(["install"]);

let name = fun_run::display(&mut cmd);

cmd.output()
    .map_err(|error| fun_run::on_system_error(name.clone(), error))
    .and_then(|output| fun_run::nonzero_captured(name.clone(), output))
    .unwrap();

Here's some fun functions you can use to help you run:

  • on_system_error - Convert std::io::Error into CmdError
  • nonzero_streamed - Produces a NamedOutput from Output that has already been streamd to the user
  • nonzero_captured - Like nonzero_streamed but for when the user hasn't already seen the output
  • display - Converts an &mut Command into a human readable string
  • display_with_env_keys - Like display but selectively shows environment variables.

Dependencies

~2.2–3.5MB
~60K SLoC