(libc.info.gz) Data Structures

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(libc.info.gz) Implementing a Shell

(libc.info.gz) Initializing the Shell

 
 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;
      }
 

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