task2.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int main(int argc, char **argv) {
    int fd[2];
    int pid;
    int res;

    if (argc != 2) {
        fprintf(stderr, "ERROR: Worng arguments!\n");
        return EXIT_FAILURE;
    }

    // Args for execvp
    char *grep[] = {"grep", argv[1], NULL};
    char *ls[] = {"ls", NULL};

    // create pipe
    pipe(fd);

    // create fork
    pid = fork();
    if (pid == 0) {
        // Child

        // Change stdout to pipe[1] and close fd read
        dup2(fd[1], 1);
        close(fd[0]);

        // run ls
        res = execvp("ls", ls);

        // close fd write
        close(fd[1]);
        exit(res);
    } else if (pid > 0) {
        // Parent:
        // Input is from pipe[0] and output is via stdout.
        dup2(fd[0], 0);
        close(fd[1]);

        // run grep
        res = execvp("grep", grep);
        close(fd[0]);
    }

    return EXIT_SUCCESS;
}