upe(6.4):A Screen at a Time Printer: p

/* upe(6.4):A Screen at a Time Printer: p
 * created on Mar 29, 2011
*/

#include    "stdio.h"

#define     PAGESIZE 22
char *progname; /* program name for error message */

/* p: print input in chunks (version 1) */

main(int argc, char *argv[])
{
    int i;
    FILE *fp, *efopen();

    progname = argv[0];
    if (argc == 1)
      printf (stdin, PAGESIZE);
    else
      for (i = 1; i < argc; i++) {
          fp = efopen(argv[i], "r");
          print(fp, PAGESIZE);
          fclose(fp);
      }
    return 0;
}

/* efopen: fopen file, die if can't */

FILE *efopen(file, mode)
{
    FILE *fp, *fopen();
    extern char *progname;

    if ((fp = fopen(file, mode)) != NULL)
      return fp;
    fprintf(stderr, "%s: can't open file %s mode %s\n",
        progname, file, mode);
    return 1;
}

/* print: print fp in pagesize chunks */
print(FILE *fp, int pagesize)
{
    static int lines = 0 ; /* number of lines so far */
    char buf[BUFSIZ];

    while (fgets(buf, sizeof buf, fp) != NULL)
      if (++lines < pagesize)
        fputs(buf, stdout);
      else {
          buf[strlen(buf)-1] = '\0';
          fputs(buf, stdout);
          fflush(stdout);
          ttyin();
          lines = 0;
      }
}

/* ttyin: process response from /dev/tty (version 1) */
ttyin()
{
    char buf[BUFSIZ];
    FILE *efopen();
    static FILE *tty = NULL;

    if (tty == NULL)
      tty = efopen("/dev/tty", "r");
    if (fgets(buf, BUFSIZ, tty) == NULL || buf[0] == 'q')
      exit(0);
    else /* ordinary line */
      return buf[0];
}