A cross-platform library for opening OS pipes.
The standard library uses pipes to read output from child processes,
but it doesn't expose a way to create them directly. This crate
fills that gap with the pipe function. It also includes some
helpers for passing pipes to the std::process::Command API.
Usage note: The main purpose of os_pipe is to support the
higher-level duct
library, which handles most of the same use cases with much less
code and no risk of deadlocks. duct can run the entire example
below in one line of code.
From<...> for File impls. While treating a pipe or a tty as
a file works pretty smoothly on Unix, it's questionable on Windows. For
example, File::metadata may return an error, or it might succeed but
then incorrectly return true from is_file. Now that the standard
library's Stdin/Stdout/Stderr types all implement
AsRawFd/AsRawHandle, callers who know what they're doing can use
those interfaces, rather than relying on os_pipe.From<PipeReader> and From<PipeWriter> for Stdio and
File. The latter is useful for APIs that require a File, like
memmap, together with dup_stdin etc. below.IntoStdio trait. Since Rust 1.20, PipeReader and
PipeWriter (as well as the standard File) can be passed directly to
std::process::Command, without any extra conversion.parent_stdin/parent_stdout/parent_stderr with
dup_stdin/dup_stdout/dup_stderr, which return
PipeReader or PipeWriter instead of Stdio.Join the stdout and stderr of a child process into a single stream, and read it. To do that we open a pipe, duplicate its write end, and pass those writers as the child's stdout and stderr. Then we can read combined output from the read end of the pipe. We have to be careful to close the write ends first though, or reading will block waiting for EOF.
```rust use os_pipe::pipe; use std::io::prelude::*; use std::process::{Command, Stdio};
// This command prints "foo" to stdout and "bar" to stderr. It // works on both Unix and Windows, though there are whitespace // differences that we'll account for at the bottom. let shell_command = "echo foo && echo bar >&2";
// Ritual magic to run shell commands on different platforms. let (shell, flag) = if cfg!(windows) { ("cmd.exe", "/C") } else { ("sh", "-c") };
let mut child = Command::new(shell); child.arg(flag); child.arg(shell_command);
// Here's the interesting part. Open a pipe, copy its write end, and // give both copies to the child. let (mut reader, writer) = pipe().unwrap(); let writerclone = writer.tryclone().unwrap(); child.stdout(writer); child.stderr(writer_clone);
// Now start the child running. let mut handle = child.spawn().unwrap();
// Very important when using pipes: This parent process is still // holding its copies of the write ends, and we have to close them // before we read, otherwise the read end will never report EOF. The // Command object owns the writers now, and dropping it closes them. drop(child);
// Finally we can read all the output and clean up the child. let mut output = String::new(); reader.readtostring(&mut output).unwrap(); handle.wait().unwrap(); assert!(output.split_whitespace().eq(vec!["foo", "bar"])); ```