waitpid

I know that waitpid() is used to wait for a process to finish, but how would one use it exactly? Here what I want to do is, create two children and wait for the first child to finish, then kill the second child before exiting. //Create two children pid_t child1; pid_t child2; child1 = fork(); //wait for child1 to finish, then kill child2 waitpid() ... child1 { kill(child2) } mf_starboi_8041 Syntax of waitpid() : pid_t waitpid(pid_t pid, int *status, int options); The value of pid can be: < -1 : Wait for any child process whose process group ID is equal to the absolute value of pid . -1 : Wait

I need to implement my shell that handles multiple pipe commands. For example I need to be able to handle this: ls | grep -i cs340 | sort | uniq | cut -c 5 . I am assuming the problem is that I am not passing output of the previous command to the input of the next command. When I execute my code, it gives me no output. I am using this pseudo code: for cmd in cmds if there is a next cmd pipe(new_fds) fork if child if there is a previous cmd dup2(old_fds[0], 0) close(old_fds[0]) close(old_fds[1]) if there is a next cmd close(new_fds[0]) dup2(new_fds[1], 1) close(new_fds[1]) exec cmd || die else

I'm trying to return an integer value from a child process. However, if I use exit(1) i get 256 as the output. exit(-1) gives 65280 . Is there a way I can get the actual int value that I send from the child process? if(!(pid=fork())) { exit(1); } waitpid(pid,&status,0); printf("%d",status); Edit: Using exit(-1) (which is what I actually want) I am getting 255 as the output for WEXITSTATUS(status). Is it supposed to be unsigned? Have you tried "man waitpid"? The value returned from the waitpid() call is an encoding of the exit value. There are a set of macros that will provide the original exit

#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> #include <sys/types.h> #include <sys/wait.h> static pid_t fork_child(void) { int pid = fork(); if (pid == -1) { perror("fork"); exit(1); } if (pid == 0) { puts("child: sleeping..."); sleep(10); puts("child: exiting"); exit(0); } return pid; } int waitpid_timeout(pid_t pid, int mseconds) { sigset_t mask, orig_mask; sigemptyset(&mask); sigaddset(&mask, SIGCHLD); if (sigprocmask(SIG_BLOCK, &mask, &orig_mask) < 0) { perror("sigprocmask"); return 1; } else { struct timespec timeout; timeout.tv_sec = mseconds / 1000;