Inter-Process Communication Using Pipes

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1️⃣ What is a Pipe?

A pipe is a unidirectional communication channel that allows one process to write data and another process to read data.

• Created using the system call:

pipe(int fd[2]);

End	Description
fd[0]	Read end
fd[1]	Write end

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2️⃣ When are Pipes Used?

• Communication between parent and child processes

• Data flows in one direction

• Used in commands like:

ls | wc

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3️⃣ How IPC Using Pipe Works

1. Parent creates a pipe

2. Parent forks a child

3. Child inherits the pipe

4. One process writes data

5. Other process reads data

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4️⃣ Important System Calls Used

System Call	Purpose
pipe()	Creates pipe
fork()	Creates child process
write()	Writes to pipe
read()	Reads from pipe
close()	Closes unused pipe ends

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5️⃣ Simple Example: Parent Writes, Child Reads

🔹 Program Explanation

• Parent sends a message to child

• Child reads and prints the message

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6️⃣ C Program: IPC Using Pipe

#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main() {
    int fd[2];
    pid_t pid;
    char message[] = "Hello from parent process";
    char buffer[100];

    // Create pipe
    if (pipe(fd) == -1) {
        perror("pipe");
        return 1;
    }

    // Create child process
    pid = fork();

    if (pid < 0) {
        perror("fork");
        return 1;
    }

    // Child process
    if (pid == 0) {
        close(fd[1]); // Close write end
        read(fd[0], buffer, sizeof(buffer));
        printf("Child received: %s\n", buffer);
        close(fd[0]);
    }
    // Parent process
    else {
        close(fd[0]); // Close read end
        write(fd[1], message, strlen(message) + 1);
        close(fd[1]);
    }

    return 0;
}

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7️⃣ Sample Output

Child received: Hello from parent process

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8️⃣ Key Points to Remember 

• Pipes are unidirectional

• Used for related processes

• Child inherits pipe descriptors

• Must close unused ends to avoid blocking