Listing 1: popen example

1  /* Listing 1
2   * popen() example
3   */
4  #include <stdio.h>
5  #define MAX_LINES   99
6  #define MAX_CHARS   4000
7  #define MAX_TXT 256
8
9  main()
10  {
11  char *slines[MAX_LINES];
12  char sbuf[MAX_CHARS];
13  char *com_str="who|sort|pr -n -t|grep -v '^[ \\t]*$'";
14  int count,i;
15
16  count=run_popen(slines, sbuf, com_str);
17  fprintf(stderr,"count is %d\n", count);
18  for(i=0; i<count;   i++)
19       printf("%s\n", slines[i]);
20  }
21  /*
22   * This function executes   a piped command passed as
23   * a pointer-to-string, exe_str.
24   * buffer is the    array where each line is stored
25   * lineptr is an array-of-pointers where each element of the
26   * array points to the beginning of each line stored in buffer.
27   *
28   * returns the number of lines read into buffer, cnt.
29   */
30  int run_popen(lineptr, buffer, exe_str)
31  char *lineptr[]; /*array-of-pointers to addresses */
32  char buffer[];  /*buffer to save strings */
33  char *exe_str;   /*pipe command */
34  {
35  int i, cnt=0;
36  FILE *ptr, *popen();
37  char *bufstart, *bufend, line[MAX_TXT], *fgets();
38
39  bufstart = buffer;         /*mark start of available space*/
40  bufend = buffer + MAX_CHARS;    /*mark end of available space*/
41  if((ptr =   popen(exe_str, "r")) == NULL)
42       fatal("Couldn't open pipe");
43
44  for(i=0; i<MAX_LINES; i++)
45       {
46       if(fgets(line, MAX_TXT, ptr) == NULL)
47          break;
48       line[strlen(line)-1] = '\0'; /* no new-lines*/
49       if((bufstart + strlen(line) + 1) >= bufend)
50          fatal("Line too long");
51       lineptr[i]=bufstart;        /*save the address of the line*/
52       strcpy(bufstart,line);      /*save the line into buffer*/
53       bufstart += strlen(line)+1; /*update starting pointer*/
54       cnt++;
55       }
56  fclose(ptr);
57  return cnt;
58  }
59  /*
60   * Fatal Error
61   */
62  int fatal(x)
63  char *x;
64  {
65  perror(x);
66  exit(1);
67  }
/* End of File */