Generate a random number in a fully POSIX compliant shell, 'dash'... Post: 303043132

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Operating Systems OS X (Apple) Generate a random number in a fully POSIX compliant shell, 'dash'... Post 303043132 by wisecracker on Sunday 19th of January 2020 04:34:56 PM

01-19-2020

Registered User

Well the C source does not compile on a current update, 19-01-2020, Linux Mint 19 using gcc 7.4.0 so here is a completely simplified and modified version for gcc 4.2.1 and 7.4.0...
The printf function will need to edited for it to work.
It is set up for Linux, (Mint 19), using gcc 7.4.0.
You can still leave to original as it is for OSX 10.14.6+ as it won't affect the performance at all, but you can edit this in instead and have both capable with the minor alteration shown...

Code:

/* 'epoch_microsecs.c' */
/* Thanks to Perderabo for this little snippet modified to suit my needs. */
/* It saved me the bother of working it out by myself. */
/* https://www.unix.com/programming/1991-time-microseconds-2.html */

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

int main(void)
{
    struct timeval tv;
    gettimeofday(&tv, NULL);

    /* Line below for gcc version 4.2.1, OSX 10.14.6... */
    /* printf("%ld.%06d", tv.tv_sec, tv.tv_usec); */

    /* Line below for gcc version 7.4.0, Linux Mint 19... */
    printf("%ld.%06ld", tv.tv_sec, tv.tv_usec);

    exit(0);
}

Last edited by wisecracker; 01-19-2020 at 06:46 PM.. Reason: Copy and paste error...

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timercmp

TIMERADD(3)						     Linux Programmer's Manual						       TIMERADD(3)

NAME

       timeradd, timersub, timercmp, timerclear, timerisset - timeval operations

SYNOPSIS

       #include <sys/time.h>

       void timeradd(struct timeval *a, struct timeval *b,
		     struct timeval *res);

       void timersub(struct timeval *a, struct timeval *b,
		     struct timeval *res);

       void timerclear(struct timeval *tvp);

       int timerisset(struct timeval *tvp);

       int timercmp(struct timeval *a, struct timeval *b, CMP);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       All functions shown above: _BSD_SOURCE

DESCRIPTION

       The macros are provided to operate on timeval structures, defined in <sys/time.h> as:

	   struct timeval {
	       time_t	   tv_sec;     /* seconds */
	       suseconds_t tv_usec;    /* microseconds */
	   };

       timeradd()  adds  the  time  values  in	a  and b, and places the sum in the timeval pointed to by res.	The result is normalized such that
       res->tv_usec has a value in the range 0 to 999,999.

       timersub() subtracts the time value in b from the time value in a, and places the result in the timeval pointed to by res.  The	result	is
       normalized such that res->tv_usec has a value in the range 0 to 999,999.

       timerclear() zeros out the timeval structure pointed to by tvp, so that it represents the Epoch: 1970-01-01 00:00:00 +0000 (UTC).

       timerisset() returns true (nonzero) if either field of the timeval structure pointed to by tvp contains a nonzero value.

       timercmp() compares the timer values in a and b using the comparison operator CMP, and returns true (nonzero) or false (0) depending on the
       result of the comparison.  Some systems (but not Linux/glibc), have a broken timercmp() implementation, in which CMP of >=, <=, and  ==	do
       not work; portable applications can instead use

	   !timercmp(..., <)
	   !timercmp(..., >)
	   !timercmp(..., !=)

RETURN VALUE

       timerisset() and timercmp() return true (nonzero) or false (0).

ERRORS

       No errors are defined.

CONFORMING TO

       Not in POSIX.1-2001.  Present on most BSD derivatives.

SEE ALSO

       gettimeofday(2), time(7)

COLOPHON

       This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2010-02-25							       TIMERADD(3)