usr/src/cmd/calendar/calendar.c

static  char *sccsid = "@(#)calendar.c  4.2 (Berkeley) 81/02/28";
/* /usr/lib/calendar produces an egrep -f file
   that will select today's and tomorrow's
   calendar entries, with special weekend provisions

   used by calendar command
*/
#include <time.h>

#define DAY (3600*24L)

char *month[] = {
        "[Jj]an",
        "[Ff]eb",
        "[Mm]ar",
        "[Aa]pr",
        "[Mm]ay",
        "[Jj]un",
        "[Jj]ul",
        "[Aa]ug",
        "[Ss]ep",
        "[Oo]ct",
        "[Nn]ov",
        "[Dd]ec"
};
struct tm *localtime();

tprint(t)
long t;
{
        struct tm *tm;
        tm = localtime(&t);
        printf("(^|[ (,;])((%s[^ ]* *|%d/)0*%d)([^0123456789]|$)\n",
                month[tm->tm_mon], tm->tm_mon + 1, tm->tm_mday);
        printf("(^|[ (,;])((\\* *)0*%d)([^0123456789]|$)\n",
                tm->tm_mday);
}

main()
{
        long t;
        time(&t);
        tprint(t);
        switch(localtime(&t)->tm_wday) {
        case 5:
                t += DAY;
                tprint(t);
        case 6:
                t += DAY;
                tprint(t);
        default:
                t += DAY;
                tprint(t);
        }
}