CODEWITHSUNDEEP
cexecforkpipegnu
Wayne Hong
Wayne Hong

Reputation: 119

C executing a pipe: execlp works while execvp doesn't

Could someone explain to me why this gives the normal behavior (ls | cat)

int fd[2]; pipe(fd);
pid_t pid = fork();
if(pid > 0) {
    close(fd[0]);
    close(STDOUT_FILENO);
    dup2(fd[1],STDOUT_FILENO);
    execlp("ls","ls",NULL);
} else if (pid == 0) {
    close(fd[1]);
    close(STDIN_FILENO);
    dup2(fd[0],STDIN_FILENO);
    execlp("cat","cat",NULL);
} else {
    error(1, errno, "forking error");
}

but when I change execlp to execvp suddenly nothing is output and exit status is 255? Code:

int fd[2]; pipe(fd);
pid_t pid = fork();
if(pid > 0) {
    close(fd[0]);
    close(STDOUT_FILENO);
    dup2(fd[1],STDOUT_FILENO);
    char **args = {"ls", NULL};
    execvp("ls",args);
} else if (pid == 0) {
    close(fd[1]);
    close(STDIN_FILENO);
    dup2(fd[0],STDIN_FILENO);
    char **args = {"cat", NULL};
    execvp("cat",args);
} else {
    error(1, errno, "forking error");
}

I'd really like to use execvp because I'll be executing commands with variable length arg lists. Help would be much appreciated.

Upvotes: 0

Views: 1309

Answers (1)

Anton Kovalenko
Anton Kovalenko

Reputation: 21507

char **args = {"ls", NULL}; should be char *args[] = {"ls", NULL};, and the same for the second args (for cat).

(It's too late here, so I can't think of the reason for the first one to compile. At least it gives a warning).

Upvotes: 2

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