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Own shell programming,linux,POSIX

Discussion in 'C' started by Exia, Apr 12, 2008.

  1. Exia

    Exia New Member

    Joined:
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    Hello everyone

    My girlfriend gave me a home-made,half-ready shell.
    It's code:

    Code:
    #define _GNU_SOURCE
    #include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <string.h>
    #include <wait.h>
    #include <ctype.h>
    
    #define LINE_LENGTH 100
    
    typedef void (*my_fork_t)(char **);
    
    int builtin_pid (char **);
    int builtin_result (char **);
    
    typedef struct builtins_t 
    {
      char *command;
      int (*function)(char **argv);
    } builtins_t;
    
    builtins_t builtins[] = {
      { "pid", builtin_pid },
      { "result", builtin_result },
      { NULL, NULL }
    };
    
    int last_result = 0;
    
    int
    builtin_pid (char **argv)
    {
      printf ("%d\n", getpid());
      return 0;
    }
    
    int
    builtin_result (char **argv)
    {
      printf ("%d\n", last_result);
      return 0;
    }
    
    
    int
    my_fork (my_fork_t fn, char **argv)
    {
      pid_t child;
      child = fork();
      if (child > 0)
        {
          int status;
          while (1)
            {
              if (waitpid (child, &status, 0) == -1)
                {
                  perror ("waitpid");
                  return -1;
                }
              if (WIFEXITED (status))
                {
                  return WEXITSTATUS (status);
                }
              else if (WIFSIGNALED (status))
                {
                  fprintf (stderr, "%s", strsignal (WTERMSIG (status)));
                  return -1;
                }
            }
        }
      else if (child == 0)
        {
          fn (argv);
          exit (0);
        }
      else
        {
          perror ("fork");
          exit (1);
        }
    }
    
    void
    run_argv (char **argv)
    {
      execvp (argv[0], argv);
      perror (argv[0]);
      exit (1);
    }
    
    #define ARGV_LIMIT 50
    
    char **
    cmdline_to_argv (char *cmdline)
    {
      int i = 0;
      char **cmd_argv = malloc (ARGV_LIMIT * sizeof (char *));
      char *p = cmdline;
      int in_word = 0;
      
      while (*p)
        {
          if (in_word)
            {
              if (isspace (*p))
                {
                  *p = 0;
                  in_word = 0;
                }
            }
          else
            {
              if (!isspace (*p))
                {
                  cmd_argv[i++] = p;
                  in_word = 1;
                }
            }
          p++;
        }
      cmd_argv[i] = NULL;
      return cmd_argv;
    }
    
    void
    free_cmd_argv (char **cmd_argv)
    {
      free (cmd_argv);
    }
    
    int
    run_command (char **argv)
    {
      int i = 0;
      while (builtins[i].command)
        {
          if (strcmp(builtins[i].command, argv[0]) == 0)
            {
              return builtins[i].function (argv);
            }
          i++;
        }
      return my_fork (run_argv, argv);
    }
    
    
    int
    main (int argc, char **argv)
    {
      char cmdline[LINE_LENGTH];
    
      while (printf ("$ "), fgets (cmdline, LINE_LENGTH, stdin))
        {
          char **cmd_argv = cmdline_to_argv (cmdline);
          if (cmd_argv[0])
            last_result = run_command (cmd_argv);
          free_cmd_argv (cmd_argv);
        }
      return 0;
    }
    
    She wants to make the "set" builtin command ,what can set an environment variable to a value,for example:' set APPLE "RINGO" ' sets the APPLE environment variable to the RINGO value.
    Unfortunately I'm not too good at POSIX prohramming,so I can't help her.
    So please if you don't mind help us.
    +She will be very happy if somebody show,how can she made a "get" bulletin, what gives back the value of an environment variable.

    Thank you for your help.
     

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