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

/* filter all characters to lower case */

/* gcc unix-simple-filter.c -o filter */

/* example of use:

   cat file.txt | filter

*/

int main(void) 
{
    int c;

    while ((c = getchar()) != EOF)
        putchar(tolower(c));

    return 0;
}