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Old 04-22-2004, 04:15 PM   #1
Linh
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C built-in function for a Bash script


Bash script
now=`date "+%s"`
The above Bash script convert today 's date to a number.

1) Are the year, month, date, hour, minutes, seconds
and thousands of a second involved in this conversion ?

2) What is the mathematical formular for this conversion ?

3) What is the C built-in function for the above Bash
script ?

Last edited by Linh; 04-22-2004 at 04:17 PM.
 
Old 04-23-2004, 03:08 AM   #2
jlliagre
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This is a 32 bit unsigned integer representing the number of seconds since what is called the epoch, January the 1st, 1970 UTC.
 
Old 04-23-2004, 04:26 AM   #3
Hko
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Re: C built-in function for a Bash script

Quote:
Originally posted by Linh
Bash script
now=`date "+%s"`
The above Bash script convert today 's date to a number.

1) Are the year, month, date, hour, minutes, seconds
and thousands of a second involved in this conversion ?
No, just seconds. But you can get the nanoseconds part of the time since the epoch with: date "+%N"
Or in C using the gettimeofday() function.

Quote:
2) What is the mathematical formular for this conversion ?
None actually. It's the other way around: The system (kernel) base format for the current time is in "number of seconds since the epoch". All other time formats are conversions from this.

Quote:
3) What is the C built-in function for the above Bash
script ?
That is the time() function. This example below does the same as: date "+%s".
Code:
#include <stdio.h>
#include <time.h>

int main()
{
	 printf("%ld\n", (long int)time(NULL));
	 return 0;
}

Last edited by Hko; 04-23-2004 at 04:29 AM.
 
Old 04-23-2004, 09:23 AM   #4
Linh
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jlliagre, and Hko. Thank you both for your help.
 
  


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