27.6.1 Data Structures for the Shell

All of the program examples included in this chapter are part of a simple shell program. This section presents data structures and utility functions which are used throughout the example.

The sample shell deals mainly with two data structures. The job type contains information about a job, which is a set of subprocesses linked together with pipes. The process type holds information about a single subprocess. Here are the relevant data structure declarations:

     /* A process is a single process.  */
     typedef struct process
     {
       struct process *next;       /* next process in pipeline */
       char **argv;                /* for exec */
       pid_t pid;                  /* process ID */
       char completed;             /* true if process has completed */
       char stopped;               /* true if process has stopped */
       int status;                 /* reported status value */
     } process;
     
     /* A job is a pipeline of processes.  */
     typedef struct job
     {
       struct job *next;           /* next active job */
       char *command;              /* command line, used for messages */
       process *first_process;     /* list of processes in this job */
       pid_t pgid;                 /* process group ID */
       char notified;              /* true if user told about stopped job */
       struct termios tmodes;      /* saved terminal modes */
       int stdin, stdout, stderr;  /* standard i/o channels */
     } job;
     
     /* The active jobs are linked into a list.  This is its head.   */
     job *first_job = NULL;

Here are some utility functions that are used for operating on job objects.

     /* Find the active job with the indicated pgid.  */
     job *
     find_job (pid_t pgid)
     {
       job *j;
     
       for (j = first_job; j; j = j->next)
         if (j->pgid == pgid)
           return j;
       return NULL;
     }
     
     /* Return true if all processes in the job have stopped or completed.  */
     int
     job_is_stopped (job *j)
     {
       process *p;
     
       for (p = j->first_process; p; p = p->next)
         if (!p->completed && !p->stopped)
           return 0;
       return 1;
     }
     
     /* Return true if all processes in the job have completed.  */
     int
     job_is_completed (job *j)
     {
       process *p;
     
       for (p = j->first_process; p; p = p->next)
         if (!p->completed)
           return 0;
       return 1;
     }