Lecture 11 CSCE 510 - Shells

• Test 1 Distribution
• Key emailed tonight
• Fork revisited
  • What is different in child and parent
  • What is inherited, what is not
  • Who goes first?
• forkStdio.c from last time
• vfork -
• Exec family
  • execve(path, newargv, environ)
  • execv(path, newargv)
  • execvp(file, newargv);
  • execle(path, *arg0, ... *argn, NULL, environ)
  • execl(path, *arg0, ... *argn, NULL)
  • execlp(file, *arg0, ... *argn, NULL)
• exec_vi.c

  #include "stdio.h"   // should be < >
  main() {
    int p;
    if ((p=fork())== 0) {
        execlp("vi","vi",NULL);
        fprintf(stderr,"EXEC FAILED\n");
    }
    sleep (5);
  
  }
  
  

• execExamples.c

  /* Examples of exec's  
   * Of course, only the first will be executed. 
   * edit the file and rearrange to test others 
   * (if you are so possessed).
   */
  #include 
  
  main(){
    char *myargv[24];  /* maximum of 24 words in a cmd */
    char **envp;       /* environment pointer to be passed */
    char **tmp;        /* temporary to help build environment*/
    char *strdup();
  
  /* Simple execve */
    myargv[0] = "env";
    myargv[1] = NULL;
    envp = (char **) malloc(15 * sizeof (char *));
    tmp = envp;
    *(tmp++) = strdup("TERM=vt101");
    *(tmp++) = strdup("SHELL=/grad/phantom/510/mysh");
    *(tmp++) = NULL;
  
  /* Just to make sure what the environment was set to
   * for(tmp = envp; *tmp != NULL; ++tmp)
   *   fprintf(stderr, "\n%s", *tmp);
   */
  
    execve("/usr/bin/env", myargv, envp);
    fatal("Exec Failed");
  
  /* Simple execv */
    myargv[0] = "ls";
    myargv[1] = "-l";
    myargv[2] = "sh.pipe.pseudo";
    myargv[3] = "execExamples.c";
    myargv[4] = NULL;
    execv("/bin/ls", myargv);
  
  /* Simple execvp */
    myargv[0] = "ls";
    myargv[1] = "-l";
    myargv[2] = "sh.pipe.pseudo";
    myargv[3] = "execExamples.c";
    myargv[4] = NULL;
    execvp("ls", myargv);
  
  
    execlp("ls", "ls", " ", NULL); /* Test if blank args cause problems */
  
    execlp("ls", "ls", "-l", NULL); /* note PATH is used to find cmd */
  }
  
  char *strdup(char * s)
  {
    char *tmp;
  
    if((tmp = (char *)malloc(strlen(s))) == (char *)NULL) exit(1);
    strcpy(tmp,s);
    return (tmp);
  }
  
  fatal(char *s)
  {
    fprintf(stderr, "\nFATAL ERROR: %s", s);
    exit(1);
  }
  
  

• execEnv.c

  #include 
  #define EOS '\0'
  extern *environ;
  main(int argc, char **argv)
  {
     char *myargv[100], *myenv[100];
  
     myargv[0] = "vi";
     myargv[1] = "testdata";
     myargv[2] = NULL;
  
     myenv[0] = "EXINIT=number";
     myenv[1] = "TERM=vt100";
     myenv[2] = NULL;
  
     if(execve("/usr/ucb/vi",myargv, myenv) < 0)
       fprintf(stderr,"Exec Failed - maybe path problem\n");
     
  }
  

• Exec and data and files
• Process Termination
• Exit
• pid_t wait(int *status)
• includes
• pid_t waitpid(pid_t pid, int *status, int option)
  • pid == -1 wait for any child
  • pid > 0 wait for specific child with pid pid
  • pid == 0, pid < -1 ... actions associated with process group
  • Options: WHOHANG,
• wait Macros
  • WIFEXITED
  • WIFSTOPPED
  • WIFSIGNALED, WTERMSIG(status)
• pid_t wait3(int *statusp, int options, struct rusage *rusage);

       #include sys/wait.h
       #include sys/time.h
       #include sys/resource.h
  

• system.c
• Shells
• Features of Shells
• Bourne Shell
• cshell
• tcshell
• korn, bash
• cshell setup files
• cshell predefined variables
• cshell history substituion
• cshell history word selection
• cshell builtin commands
• cshell filename expansion

  
       int
       match(const char *string, char *pattern)
       {
             int status;
             regex_t re;
             if (regcomp(&re, pattern, REG_EXTENDED|REG_NOSUB) != 0) {
                  return(0);      /* report error */
             }
             status = regexec(&re, string, (size_t) 0, NULL, 0);
             regfree(&re);
             if (status != 0) {
                   return(0);      /* report error */
             }
             return(1);
       }
  

• cshell alias substitution
• cshell command substitution
• Shell Implementation
  1. write prompt
  2. read command line
  3. parse into linked list of words
  4. perform substitutions
  5. remap Standard IO
  6. build argv
  7. fork/exec

[Readings:]

[Assignment:]

1. Write a "match program" that will read a line of input, break it into words, inserting each into a linked (maybe doubly linked list). Then print the list. Then read a match pattern and match it against the name of every file in the current directory.