% cat  popen.c

/* A program to demonstrate some of the nifty UNIX capabilities in C */

#include <stdio.h>

main()

{
  FILE *pipefp;
  char tmp[100];

  printf("Opening Pipe...\n");

  pipefp = popen("ls -l","r");
  if ( pipefp == NULL ) {
    fprintf(stderr,"Unable to open pipe\n");
    exit();
  }

  while(fgets(tmp,100,pipefp) != NULL ) {
    printf("Line: %s",tmp);
  }  /* End while */

  pclose(pipefp);

}
% cc  popen.c
% a.out 
Opening Pipe...
Line: -rwx------   1 crs      cl          4669 Aug 16 11:11 a.out
Line: -rw-------   1 crs      cl           682 Aug 16 09:13 fun3.c
Line: -rw-------   1 crs      cl          1652 Dec  7 1993  gradepretty.c
Line: -rw-------   1 crs      cl           110 Dec  7 1993  gradepretty.dat
Line: -rw-------   1 crs      cl           985 Dec  8 1993  grades.c
Line: -rw-------   1 crs      cl           402 Aug 16 11:10 popen.c
Line: -rw-------   1 crs      cl           442 Dec  7 1993  quad.c
Line: -rw-------   1 crs      cl           810 Aug 16 10:43 quadfun.c
Line: -rw-------   1 crs      cl          1009 Dec  7 1993  quadsub.C
Line: -rw-------   1 crs      cl           578 Dec  7 1993  tempconv.c
%