Convert UNIX time_t into a date/time text string

Often times, when working with the standard Linux/UNIX time format (time_t) one needs to quickly find out what is the “human readable” date and time text string a particular time_t value corresponds to.

NOTE: The ‘C’ time_t type is the number of seconds elapsed since the “epoch”, the epoch being January 1st 1970 at 00:00:00.

As much as I tried to find a standard *NIX command to do the job I couldn’t.. Eventually I wrote a C two-liner to do the job but I am still curious if there is a standard shell command to do the job, so if anybody knows of one I would appreciate a comment… 🙂

As far as writing it yourself this line of code will do the job :
printf("UNIX time %ld is: %s\n", time_t_var, ctime( &time_t_var ) );
, where the variable time_t_var holds the time_t value…

Because ctime is used to convert time_t into a datetime text string, the text will display the date and time taking into account the current locale settings (timezone and summer time). If you want a ‘raw’ UTC/GMT representation of the time_t value then use gmtime()..

An example using both functions follows:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int main(int argc, char **argv)
{
    time_t  time_t_var;

    if (argc > 1)
    {
        time_t_var = atoi(argv[1]);
    }
    else
    {
        time_t_var = time((time_t *) NULL);
    }

    printf( "UNIX time %ld is: %s (ctime)\n",
            time_t_var, ctime( &time_t_var ) );

    struct tm tm_val;
    gmtime_r( &time_t_var, &tm_val );
    printf( "UNIX time %ld is: %s (gmtime)\n",
            time_t_var, asctime(&tm_val) );

    return 0;
}