Mastering Child Process Interaction with Pipes

Introduction

In this lab, the usage of std::Child struct to represent a running child process and its interaction through pipes with the stdin, stdout, and stderr handles is demonstrated.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL rust(("Rust")) -.-> rust/FunctionsandClosuresGroup(["Functions and Closures"]) rust(("Rust")) -.-> rust/AdvancedTopicsGroup(["Advanced Topics"]) rust(("Rust")) -.-> rust/MemorySafetyandManagementGroup(["Memory Safety and Management"]) rust(("Rust")) -.-> rust/DataStructuresandEnumsGroup(["Data Structures and Enums"]) rust(("Rust")) -.-> rust/ErrorHandlingandDebuggingGroup(["Error Handling and Debugging"]) rust(("Rust")) -.-> rust/BasicConceptsGroup(["Basic Concepts"]) rust(("Rust")) -.-> rust/DataTypesGroup(["Data Types"]) rust/BasicConceptsGroup -.-> rust/variable_declarations("Variable Declarations") rust/BasicConceptsGroup -.-> rust/mutable_variables("Mutable Variables") rust/DataTypesGroup -.-> rust/string_type("String Type") rust/FunctionsandClosuresGroup -.-> rust/function_syntax("Function Syntax") rust/FunctionsandClosuresGroup -.-> rust/expressions_statements("Expressions and Statements") rust/MemorySafetyandManagementGroup -.-> rust/lifetime_specifiers("Lifetime Specifiers") rust/DataStructuresandEnumsGroup -.-> rust/method_syntax("Method Syntax") rust/ErrorHandlingandDebuggingGroup -.-> rust/panic_usage("panic! Usage") rust/AdvancedTopicsGroup -.-> rust/operator_overloading("Traits for Operator Overloading") subgraph Lab Skills rust/variable_declarations -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/mutable_variables -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/string_type -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/function_syntax -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/expressions_statements -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/lifetime_specifiers -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/method_syntax -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/panic_usage -.-> lab-99274{{"Child Process Interaction with Pipes"}} rust/operator_overloading -.-> lab-99274{{"Child Process Interaction with Pipes"}} end

Pipes

The std::Child struct represents a running child process, and exposes the stdin, stdout and stderr handles for interaction with the underlying process via pipes.

use std::io::prelude::*;
use std::process::{Command, Stdio};

static PANGRAM: &'static str =
"the quick brown fox jumped over the lazy dog\n";

fn main() {
    // Spawn the `wc` command
    let process = match Command::new("wc")
                                .stdin(Stdio::piped())
                                .stdout(Stdio::piped())
                                .spawn() {
        Err(why) => panic!("couldn't spawn wc: {}", why),
        Ok(process) => process,
    };

    // Write a string to the `stdin` of `wc`.
    //
    // `stdin` has type `Option<ChildStdin>`, but since we know this instance
    // must have one, we can directly `unwrap` it.
    match process.stdin.unwrap().write_all(PANGRAM.as_bytes()) {
        Err(why) => panic!("couldn't write to wc stdin: {}", why),
        Ok(_) => println!("sent pangram to wc"),
    }

    // Because `stdin` does not live after the above calls, it is `drop`ed,
    // and the pipe is closed.
    //
    // This is very important, otherwise `wc` wouldn't start processing the
    // input we just sent.

    // The `stdout` field also has type `Option<ChildStdout>` so must be unwrapped.
    let mut s = String::new();
    match process.stdout.unwrap().read_to_string(&mut s) {
        Err(why) => panic!("couldn't read wc stdout: {}", why),
        Ok(_) => print!("wc responded with:\n{}", s),
    }
}

Summary

Congratulations! You have completed the Pipes lab. You can practice more labs in LabEx to improve your skills.