Why is execv doesn't work in sort command-CodePudding

Hi I'm trying to use execv function in forked child process to execute the commands like: ls, grep, sort, awk and so on in terminal. However, ls, grep works but sort, awk and other things are not working and execv returns -1 for failure. Inputs for argv was "sort t.txt" by stdin and argv[0]=sort, argv[1]=t.txt. When I put in grep 5 t.txt for example, it printed out 3 numbers in t.txt that includes 5 and ls printed out every file in directory. Why do only ls and grep work and rest of commands don't?

    char* command(char** argv) {
       char* ptr = malloc(200);
       if (!strcmp(argv[0], "ls") || !strcmp(argv[0], "man") || !strcmp(argv[0], "grep")
        || !strcmp(argv[0], "sort") || !strcmp(argv[0], "awk") || !strcmp(argv[0], "bc")) {
           sprintf(ptr, "/bin/%s", argv[0]);
       }
       return ptr;
    }
    
    //inside fork=
    char* pos = command(argv);
    if (execv(pos, argv) < 0) {
       printf("%s\n", argv[0]);
       if(argv[1]!=NULL)
          printf("%s\n", argv[1]);
       if(argv[2]!=NULL)
          printf("%s\n", argv[2]);
       perror("execv");
       fprintf(stderr, "%s: Command not found.\n", argv[0]);
       free(pos);
       exit(0);
    }
    free(pos);

   mini> sort t
   sort
   t
   execv: No such file or directory
   sort: Command not found.
   mini> ls
   Makefile  minishell.c  pa2  t
   mini>

CodePudding user response：

The problem is because you hard-code the commands to be found in /bin/, and some commands (like the sort command) isn't in that location (sort is typically in /usr/bin/).

To solve that problem, and to be able to use any command in the standard path, use execvp instead:

execvp(argv[0], argv);

The difference from execv is that execvp will use the environment variable PATH to search for the command.

Please read the exec family manual page for details about the different versions.