Crate cradle

(cradle is in an early stage of development. APIs may change drastically! Use at your own risk!)

cradle provides the run! macro, that makes it easy to run child processes from rust programs.

use cradle::prelude::*;
use std::path::Path;

run!(%"touch foo");
assert!(Path::new("foo").is_file());

Input

You can pass in multiple arguments (of different types) to run! to specify arguments, as long as they implement the Input trait:

use cradle::prelude::*;
use std::path::Path;

run!("mkdir", "-p", "foo/bar/baz");
assert!(Path::new("foo/bar/baz").is_dir());

For all possible inputs to run!, see the documentation of Input.

Output

cradle also provides a run_output! macro. It allows to capture outputs of the child process. It uses return-type polymorphism, so you can control which outputs are captured by choosing the return type of run_output!. The only constraint is that the chosen return type has to implement Output. For example you can use e.g. StdoutTrimmed to collect what the child process writes to stdout, trimmed of leading and trailing whitespace:

use cradle::prelude::*;

let StdoutTrimmed(output) = run_output!(%"echo foo");
assert_eq!(output, "foo");

(By default, the child’s stdout is written to the parent’s stdout. Using StdoutTrimmed as the return type suppresses that.)

If you don’t want any result from run_output!, you can use () as the return value:

use cradle::prelude::*;

let () = run_output!(%"touch foo");

Since that’s a very common case, cradle provides the run! shortcut, that we’ve already seen above. It behaves exactly like run_output! but always returns ():

use cradle::prelude::*;

run!(%"touch foo");

See the implementations for output::Output for all the supported types.

Whitespace Splitting of Inputs

cradle does not split given string arguments on whitespace by default. So for example this code fails:

use cradle::prelude::*;

let StdoutTrimmed(_) = run_output!("echo foo");

In this code cradle tries to run a process from an executable called "echo foo", including the space in the file name of the executable. That fails, because an executable with that name doesn’t exist. cradle provides a new-type wrapper Split to help with that:

use cradle::prelude::*;

let StdoutTrimmed(output) = run_output!(Split("echo foo"));
assert_eq!(output, "foo");

Wrapping an argument of type &str in Split will cause cradle to first split it by whitespace and then use the resulting words as if they were passed into run_output! as separate arguments.

And – since this is such a common case – cradle provides a syntactic shortcut for Split, the % symbol:

use cradle::prelude::*;

let StdoutTrimmed(output) = run_output!(%"echo foo");
assert_eq!(output, "foo");

Error Handling

By default run! and run_output! panic for a few reasons, e.g.:

• when the child process exits with a non-zero exitcode,
• when the given executable cannot be found,
• when no strings are given as arguments.

For example:

use cradle::prelude::*;

// panics with "false:\n  exited with exit code: 1"
run!("false");

You can suppress panics caused by non-zero exit codes by using the Status type as a return type of run_output!:

use cradle::prelude::*;

let Status(exit_status) = run_output!("false");
assert_eq!(exit_status.code(), Some(1));

You can also turn all panics into std::result::Result::Errs by using run_result!. This will return a value of type Result<T, cradle::Error>, where T is any type that implements output::Output. Here’s some examples:

use cradle::prelude::*;

let result: Result<(), cradle::Error> = run_result!("false");
let error_message = format!("{}", result.unwrap_err());
assert_eq!(
    error_message,
    "false:\n  exited with exit code: 1"
);

let result = run_result!(%"echo foo");
let StdoutTrimmed(output) = result.unwrap();
assert_eq!(output, "foo".to_string());

run_result! can also be combined with ? to handle errors in an idiomatic way, for example:

use cradle::prelude::*;

fn build() -> Result<(), Error> {
    run_result!(%"which make")?;
    run_result!(%"which gcc")?;
    run_result!(%"which ld")?;
    run_result!(%"make build")?;
    Ok(())
}

Alternative Interface: Methods on input::Input

cradle also provides an alternative interface to execute commands through methods on the Input trait: .run(), .run_output() and .run_result(). These methods can be invoked on all values whose types implement Input. When using these methods, it’s especially useful that Input is implemented by tuples. They work analog to run!, run_output! and run_result!. Here are some examples:

use cradle::prelude::*;

("touch", "foo").run();

let StdoutTrimmed(output) = ("echo", "foo").run_output();
assert_eq!(output, "foo");

let result: Result<(), cradle::Error> = "false".run_result();
let error_message = format!("{}", result.unwrap_err());
assert_eq!(
    error_message,
    "false:\n  exited with exit code: 1"
);

Note: The % shortcut for Split is not available in this notation. You can either use tuples, or Split explicitly:

use cradle::prelude::*;

("echo", "foo").run();
Split("echo foo").run();

Prior Art

cradle is heavily inspired by shake, specifically by its cmd function.

Re-exports

pub use crate::error::Error;

Modules

error

The Error type used in the return type of run_result!.

input

The Input trait that defines all possible inputs to a child process.

output

The Output trait that defines all possible outputs of a child process.

prelude

cradle’s prelude module. It re-exports the most commonly used items from cradle. We recommend importing cradle like this: use cradle::prelude::*;

Macros

run

Executes a child process without capturing any output.

run_output

Execute child processes, and capture some output. For example you can capture what the child process writes to stdout:

run_result

Like run_output!, but fixes the return type to Result<T, Error>, where T is any type that implements Output.