simple_shell.c

   1 #include <unistd.h>
   2 #include <sys/time.h>
   3 #include <sys/resource.h>
   4 #include <stdio.h>
   5 #include <sys/types.h>
   6 #include <sys/wait.h>
   7 #include <stdarg.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10
  11 #define MAXLINE 100
  12 #define MAXARGS 20
  13
  14 int parseline(const char *cmdline, char **argv);
  15 void do_bgfg(char *cmdline);
  16
  17 void eval (char *cmdline) {
  18     char *argv[MAXARGS];
  19     int bg;
  20     pid_t pid;
  21
  22     bg = parseline(cmdline, argv);
  23     if ((pid = fork()) == 0) {   /* child runs command */
  24         if (execvp(argv[0], argv) < 0) {
  25             perror("Command not found");
  26             exit(0);
  27         }
  28     }
  29     if (!bg) { /* parent waits for fg job to terminate */
  30         int status;
  31         if (waitpid(pid, &status, 0) < 0) {
  32             perror("waitfg: waitpid error");
  33         }
  34     }
  35     else { /* otherwise, don’t wait for bg job */
  36         printf("%d %s\n", pid, cmdline);
  37     }
  38 }
  39
  40 int main () {
  41     char cmdline[MAXLINE];
  42     while (1) {
  43         /* read */
  44         printf("> ");
  45         fgets(cmdline, MAXLINE, stdin);
  46         if (feof(stdin)) {
  47             exit(0);
  48         }
  49         /* evaluate */
  50         eval(cmdline);
  51     }   /* loop! */
  52     return 0;
  53 }
  54
  55 int parseline(const char *cmdline, char **argv)
  56 {
  57     static char array[MAXLINE]; /* holds local copy of command line */
  58     char *buf = array;          /* ptr that traverses command line */
  59     char *delim;                /* points to first space delimiter */
  60     int argc;                   /* number of args */
  61     int bg;                     /* background job? */
  62
  63     strcpy(buf, cmdline);
  64     buf[strlen(buf)-1] = ' ';   /* replace trailing '\n' with space */
  65     while (*buf && (*buf == ' ')) /* ignore leading spaces */
  66         buf++;
  67
  68     /* Build the argv list */
  69     argc = 0;
  70     if (*buf == '\'') {
  71         buf++;
  72         delim = strchr(buf, '\'');
  73     }
  74     else {
  75         delim = strchr(buf, ' ');
  76     }
  77
  78     while (delim) {
  79         argv[argc++] = buf;
  80         *delim = '\0';
  81         buf = delim + 1;
  82         while (*buf && (*buf == ' ')) /* ignore spaces */
  83             buf++;
  84
  85         if (*buf == '\'') {
  86             buf++;
  87             delim = strchr(buf, '\'');
  88         }
  89         else {
  90             delim = strchr(buf, ' ');
  91         }
  92     }
  93     argv[argc] = NULL;
  94
  95     if (argc == 0)  /* ignore blank line */
  96         return 0;
  97
  98     /* should the job run in the background? */
  99     if ((bg = (*argv[argc-1] == '&')) != 0) {
 100         argv[--argc] = NULL;
 101     }
 102     return bg;
 103 }
 104 void do_bgfg(char *cmdline){
 105
 106 }