how to write ls command in c using execvp

Question

i am trying to write a simple ls command so i'm input "ls r" and i want to check if my code is allright. the output does not showing anything. this is the code:

int main(void){

  char *line;
  char *args[16];
  pid_t pid; 

    line = (char*)malloc(1024);
    printf("$ "); 
    fgets(line,1024,stdin);
     args[0] = strtok(line, " ");
     args[1] = strtok(NULL, " "); 

    printf("%s\n" , args[0]);
    printf("%s", args[1]);

    execvp(args[0], args);
}

thanks all.

Answer 1

Look inside the source code of existing free software shells (ie sash or bash ) and read Advanced Linux Programming

Read execvp(3) man page. Notice that execvp can fail. When it succeeds, it does not return ! Also, stdout(3) is buffered , you need to call fflush(3) .

You are probably missing some basic understanding (a shell is forking processes, read also fork(2) & execve(2) etc...)

Try first:

int main(void){
 char line[1024];
 char *args[16];
 memset (args, 0, sizeof(args));
 printf("$ ");
 fflush(NULL); 
 fgets(line,sizeof(line),stdin);
 args[0] = strtok(line, " ");
 args[1] = strtok(NULL, " "); 
 printf("%s\n" , args[0]);
 printf("%s", args[1]);
 fflush(NULL);
 execvp(args[0], args);
 perror("execvp");
 return EXIT_FAILURE;
}

Don't forget the relevant #include directives needed by fflush(3) , fgets , execvp , perror .

Read also errno(3) , syscalls(2) ...

Compile using gcc -Wall -g . Learn how to use the debugger gdb and also strace

BTW, real shells don't use strtok(3) ; they parse the line explicitly (and they have to, since a shell can escape a space with a backslash or a quote).

Actually, try strace ls ; you'll find out that /bin/ls uses stat(2) .