Shell Programming and Scripting

$ cat unixdate
#! /usr/bin/ksh
epoch=1297969816
((uday=epoch/86400))   # 86400 seconds in a day
((uday=uday+40587))    # 40587 is the modified julian day number of Jan 1, 1970
./datecalc -j $uday
$
$ ./unixdate
2011 2 17
$

/*******************************************************************************
 * File:        convtime.c
 *
 * Description: Convert OpCdatetime (seconds since EPOCH) to calendar datetime.
 *              Calendar datetime is written to stdout.
 *
 * Use:        convtime <OpCdatetime>
 *
 * Revision History
 * ================
 *
 * Name        Date    Description
 * J. Peereboom 960722    Creation
 * 
 ******************************************************************************/

/*
 * System includes
 */
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <time.h>

/*******************************************************************************
 * Function:    main()
 * Description: Main entry point.
 * Called by:   None
 * In:          argc: Argument count.
 *              argv: The arguments. argv[1] is the datetime to be converted.
 * Out:         None
 * InOut:       None
 * Return:      0.
 *              Prints the calendar datetime on stdout.
 ******************************************************************************/

extern int main(argc, argv)
 int   argc;
 char *argv[];
{
    struct tm *t;
    time_t seconds;

    if (argc != 2)
    {
    fprintf(stderr,"usage: doit time\n");
    exit(1);
    }

    sscanf (argv[1], "%ld", &seconds);
    t = localtime(&seconds);
    printf("%4d%02d%02d %02d:%02d:%02d\n"
            , t->tm_year+1900
            , t->tm_mon+1
            , t->tm_mday
                        , t->tm_hour
            , t->tm_min
            , t->tm_sec
            );
    return 0;
}

$ printf "%(%Y-%m-%d)T\n" #1297969816
2011-02-17