Crate cradle

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

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

use cradle::prelude::*;

let StdoutTrimmed(stdout) = cmd!(%"echo foo");
assert_eq!(stdout, "foo");

Arguments

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

use cradle::prelude::*;

let StdoutTrimmed(stdout) = cmd!("echo", "foo", "bar");
assert_eq!(stdout, "foo bar");

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

Whitespace Splitting

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

use cradle::prelude::*;

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

Output

You can choose which return type you want cmd! to return, as long as the chosen return type implements 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) = cmd!(%"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 cmd!, you can use () as the return value:

use cradle::prelude::*;

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

Since that’s a very common case, cradle provides the cmd_unit! shortcut. It’s named after the unit type (). It behaves exactly like cmd! but always returns ().

use cradle::prelude::*;

cmd_unit!(%"touch foo");

See the implementations for Output for all the supported types.

Error Handling

By default cmd! panics 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 to cmd!.

For example:

use cradle::prelude::*;

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

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

use cradle::prelude::*;

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

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

use cradle::prelude::*;

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

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

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

use cradle::prelude::*;

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

Alternative interface

cradle also provides an alternative interface to execute commands through methods on the Input trait: .run(), .run_unit() 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 cmd!, cmd_unit! and cmd_result!. Here are some examples:

use cradle::prelude::*;

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

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

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_unit();
Split("echo foo").run_unit();

Prior Art

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

Re-exports

pub use error::Error;

Modules

error

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

input

The Input trait that defines all possible inputs to cmd!, cmd_unit! and cmd_result!.

output

The Output trait that defines all possible outputs of cmd!, cmd_unit! and cmd_result!.

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

cmd

Execute child processes. See the module documentation on how to use it.

cmd_result

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

cmd_unit

Like cmd!, but fixes the return type to (). It’s named after the unit type ().