# 1.0.0[−][src]Trait std::os::unix::process::CommandExt

    pub trait CommandExt {
        fn uid(&mut self, id: u32) -> &mut Command;
        fn gid(&mut self, id: u32) -> &mut Command;
        fn before_exec<F>(&mut self, f: F) -> &mut Command
        where
            F: FnMut() -> Result<()> + Send + Sync + 'static;
        fn exec(&mut self) -> Error;
    }

This is supported on Unix only.

Unix-specific extensions to the `process::Command` builder.

## Required methods

### `fn uid(&mut self, id: u32) -> &mut Command`

This is supported on Unix only.

Sets the child process's user id. This translates to a `setuid` call in the child process. Failure in the `setuid` call will cause the spawn to fail.

### `fn gid(&mut self, id: u32) -> &mut Command`

This is supported on Unix only.

Similar to `uid`, but sets the group id of the child process. This has the same semantics as the `uid` field.

### `fn before_exec<F>(&mut self, f: F) -> &mut Command where
F: FnMut() -> Result<()> + Send + Sync + 'static,`
1.15.0

This is supported on Unix only.

Schedules a closure to be run just before the `exec` function is invoked.

The closure is allowed to return an I/O error whose OS error code will be communicated back to the parent and returned as an error from when the spawn was requested.

Multiple closures can be registered and they will be called in order of their registration. If a closure returns `Err` then no further closures will be called and the spawn operation will immediately return with a failure.

# Notes

This closure will be run in the context of the child process after a `fork`. This primarily means that any modifications made to memory on behalf of this closure will not be visible to the parent process. This is often a very constrained environment where normal operations like `malloc` or acquiring a mutex are not guaranteed to work (due to other threads perhaps still running when the `fork` was run).

When this closure is run, aspects such as the stdio file descriptors and working directory have successfully been changed, so output to these locations may not appear where intended.

### `fn exec(&mut self) -> Error`
1.9.0

This is supported on Unix only.

Performs all the required setup by this `Command`, followed by calling the `execvp` syscall.

On success this function will not return, and otherwise it will return an error indicating why the exec (or another part of the setup of the `Command`) failed.

`exec` not returning has the same implications as calling `process::exit` – no destructors on the current stack or any other thread’s stack will be run. Therefore, it is recommended to only call `exec` at a point where it is fine to not run any destructors. Note, that the `execvp` syscall independently guarantees that all memory is freed and all file descriptors with the `CLOEXEC` option (set by default on all file descriptors opened by the standard library) are closed.

This function, unlike `spawn`, will not `fork` the process to create a new child. Like spawn, however, the default behavior for the stdio descriptors will be to inherited from the current process.

# Notes

The process may be in a "broken state" if this function returns in error. For example the working directory, environment variables, signal handling settings, various user/group information, or aspects of stdio file descriptors may have changed. If a "transactional spawn" is required to gracefully handle errors it is recommended to use the cross-platform `spawn` instead.

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## Implementors

### `impl CommandExt for Command`[src]

#### `fn uid(&mut self, id: u32) -> &mut Command`[src]

This is supported on Unix only.

#### `fn gid(&mut self, id: u32) -> &mut Command`[src]

This is supported on Unix only.

#### `fn before_exec<F>(&mut self, f: F) -> &mut Command where
F: FnMut() -> Result<()> + Send + Sync + 'static,` [src]

This is supported on Unix only.

#### `fn exec(&mut self) -> Error`[src]

This is supported on Unix only.
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