Re: Bash unable to print epoch timestamp

[Brian Inglis <Brian dot Inglis at SystematicSw dot ab dot ca>]

Brian Inglis <Brian.Inglis <at> SystematicSw.ab.ca> writes:

> 
> Don Harrop <don <at> effx.us> writes:
> > Bash outputs no value when using it's built in method of printing an 
> > "epoch" timestamp.
> > BashCommandLine#: printf '%(%s)T' -1
> 
> bash printf depends on underlying strftime in newlib, which does not support
> %s, as it is conditional on _WANT_C99_TIME_FORMATS being defined, and that
> is presumably not defined in the config, as %s is not shown in man strftime. 
> Workaround for now is use 
>     date +%s 
> for current time, and 
>    date -d $(printf '%(%T)T' -2) +%s
> for shell invocation time.

> %s, as it is conditional on _WANT_C99_TIME_FORMATS being defined, and that
Wrong! Misread the code, strftime %s is not supported! 

STC and suggested patch appended (posting from gmane), compiles, but can't
build STC as ld fails with undef refs, and I don't know all the correct
LD..., -L and -l incantations. Email me for original files. 

/* newlib/time/strftime.c %s format STC */
#include <stdio.h>
#include <time.h>

int main( int argc, char **argv) {
    char ss[BUFSIZ]     = "";
    time_t tt           = time( NULL );
    struct tm *tp       = gmtime( &tt );
    tt                  = mktime( tp );
    size_t st           = strftime( ss, sizeof ss, "%s", tp);
    int rc              = puts( ss );
    st                  = strftime( ss, sizeof ss, "%T", tp);
    rc                  = puts( ss );
    return rc;
}

--- 8< ---
2015-10-12  Brian Inglis  <Brian.Inglis@SystematicSw.ab.ca>
* newlib/time/strftime.c (__strftime): add support for %s (seconds from Unix
epoch)

--- a/newlib/time/strftime.c        2015-08-20 03:39:24.000000000 -0600
+++ b/newlib/time/strftime.c        2015-10-21 20:15:22.367453000 -0600
@@ -166,6 +166,10 @@ notations, the result is an empty string
 o %R
 The 24-hour time, to the minute.  Equivalent to "%H:%M". [tm_min, tm_hour]

+o %s
+The time elapsed, in seconds, since the start of the Unix epoch at
+1970-01-01 00:00:00 UTC.
+
 o %S
 The second, formatted with two digits (from `<<00>>' to `<<60>>').  The
 value 60 accounts for the occasional leap second. [tm_sec]
@@ -1109,6 +1113,74 @@ recurse:
                          tim_p->tm_hour, tim_p->tm_min);
           CHECK_LENGTH ();
           break;
+       case CQ('s'):
+/*
+ * From:
+ * The Open Group Base Specifications Issue 7
+ * IEEE Std 1003.1, 2013 Edition
+ * Copyright (c) 2001-2013 The IEEE and The Open Group
+ * XBD Base Definitions
+ * 4. General Concepts
+ * 4.15 Seconds Since the Epoch
+ * A value that approximates the number of seconds that have elapsed since the
+ * Epoch. A Coordinated Universal Time name (specified in terms of seconds
+ * (tm_sec), minutes (tm_min), hours (tm_hour), days since January 1 of the
year
+ * (tm_yday), and calendar year minus 1900 (tm_year)) is related to a time
+ * represented as seconds since the Epoch, according to the expression below.
+ * If the year is <1970 or the value is negative, the relationship is
undefined.
+ * If the year is >=1970 and the value is non-negative, the value is
related to a
+ * Coordinated Universal Time name according to the C-language expression,
where
+ * tm_sec, tm_min, tm_hour, tm_yday, and tm_year are all integer types:
+ * tm_sec + tm_min*60 + tm_hour*3600 + tm_yday*86400 +
+ *     (tm_year-70)*31536000 + ((tm_year-69)/4)*86400 -
+ *     ((tm_year-1)/100)*86400 + ((tm_year+299)/400)*86400
+ * OR
+ * ((((tm_year-69)/4 - (tm_year-1)/100 + (tm_year+299)/400 +
+ *         (tm_year-70)*365 + tm_yday)*24 + tm_hour)*60 + tm_min)*60 + tm_sec
+ */
+/* modified from %z case by hoisting offset outside if block and
initializing */
+         {
+           long offset;        /* offset < 0 => W of GMT, > 0 => E of GMT:
+           offset = 0;    subtract to get UTC */
+
+           if (tim_p->tm_isdst >= 0)
+             {
+               TZ_LOCK;
+               if (!tzset_called)
+                 {
+                   _tzset_unlocked ();
+                   tzset_called = 1;
+                 }
+
+#if defined (__CYGWIN__)
+               /* Cygwin must check if the application has been built with or
+                  without the extra tm members for backward compatibility, and
+                  then use either that or the old method fetching from tzinfo.
+                  Rather than pulling in the version check infrastructure, we
+                  just call a Cygwin function. */
+               extern long __cygwin_gettzoffset (const struct tm *tmp);
+               offset = __cygwin_gettzoffset (tim_p);
+#elif defined (__TM_GMTOFF)
+               offset = tim_p->__TM_GMTOFF;
+#else
+               __tzinfo_type *tz = __gettzinfo ();
+               /* The sign of this is exactly opposite the envvar TZ.  We
+                  could directly use the global _timezone for tm_isdst==0,
+                  but have to use __tzrule for daylight savings.  */
+               offset = -tz->__tzrule[tim_p->tm_isdst > 0].offset;
+#endif
+               TZ_UNLOCK;
+             }
+           len = snprintf (&s[count], maxsize - count, CQ("%lld"),
+                           (((((long long)tim_p->tm_year - 69)/4
+                               - (tim_p->tm_year - 1)/100
+                               + (tim_p->tm_year + 299)/400
+                               + (tim_p->tm_year - 70)*365 + tim_p->tm_yday)*24
+                             + tim_p->tm_hour)*60 + tim_p->tm_min)*60
+                           + tim_p->tm_sec - offset);
+           CHECK_LENGTH ();
+         }
+          break;
        case CQ('S'):
 #ifdef _WANT_C99_TIME_FORMATS
          if (alt != CQ('O') || !*alt_digits
@@ -1442,6 +1514,7 @@ const struct test  Vec0[] = {
        { CQ("%p"), 2+1, EXP(CQ("AM")) },
        { CQ("%r"), 11+1, EXP(CQ("09:53:47 AM")) },
        { CQ("%R"), 5+1, EXP(CQ("09:53")) },
+       { CQ("%s"), 2+1, EXP(CQ("1230648827")) },
        { CQ("%S"), 2+1, EXP(CQ("47")) },
        { CQ("%t"), 1+1, EXP(CQ("\t")) },
        { CQ("%T"), 8+1, EXP(CQ("09:53:47")) },



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