/* establishes a pipe between the OS and a program(e.g ls | uppercase) */

#include <stdio.h>
#include <ctype.h>

main()
{
  int c;
  FILE *ifp;

  ifp = popen("ls", "r"); /* open a pipe to read the output of ls */
  while ((c = getc(ifp)) != EOF)
	putchar(toupper(c));
  pclose(ifp);
}