--------------------------------------------- 
$ pico copy1.c
#include <stdio.h>
/* copy1.c - copy input to output, version 1 */
main()
{
    int c;
    c = getchar();
    while (c != EOF) {
        putchar(c);
        c = getchar();
    }
}
^X
$ gcc copy1.c
$ ls  
a.out  copy1.c
$ a.out
AAAAA
AAAAA
^D
$ ./a.out < copy1.c > anothercopy.c
$ ./a.out < a.out > copy
ls
a.out  copy  copy1.c  anothercopy.c
$ ./copy < anothercopy.c > yetanothercopy.c
bash: ./copy: Permission denied
% chmod 770 copy
$ ./copy < anothercopy.c > yetanothercopy.c
$ ls
a.out  copy  copy1.c  anothercopy.c  yetanothercopy.c
-------------------------------------------
1. getchar() inputs a character (8-bit byte) and
   putchar() outputs a character.
2. getchar returns a 16-bit (or larger) int so that we can
   differentiate between an input byte of all 1's
   (0000000011111111) and the End Of File (1111111111111111).
3. Control D (^D) is keyboard EOF.
4. EOF (along with getchar and putchar) defined in <stdio.h>.
-------------------------------------------