.\" auto generated by yuck -*- nroff -*-
.TH DATEDIFF "1" "May 2022" "dateutils 0.4.10" "User Commands"
.SH NAME
datediff - Compute duration from DATE/TIME (the reference date/time) to the other
.SH SYNOPSIS
.B datediff
[\fIOPTION\fR]... 
DATE/TIME \fI\fR[\fIDATE/TIME\fR]\fR...
.SH DESCRIPTION
Compute duration from DATE/TIME (the reference date/time) to the other
DATE/TIMEs given and print the result as duration.
If the other DATE/TIMEs are omitted read them from stdin.

DATE/TIME can also be one of the following specials
  - `now'           interpreted as the current (UTC) time stamp
  - `time'          the time part of the current (UTC) time stamp
  - `today'         the current date (according to UTC)
  - `tomo[rrow]'    tomorrow's date (according to UTC)
  - `y[ester]day'   yesterday's date (according to UTC)

Note: The output format of durations (specified via -f) takes all format
specifiers into account, i.e. specifying %M and %S for example prints the
duration in minutes and seconds, whereas specifying %S only prints the duration
in seconds.

See section `The refinement rule' in ddiff(1).

.PP

Recognized \fIOPTION\fRs:
.TP
.B   \fB-h\fR, \fB--help
Print help and exit
.TP
.B   \fB-V\fR, \fB--version
Print version and exit
.TP
.B   \fB-q\fR, \fB--quiet
Suppress message about date/time and duration
parser errors and fix-ups.
The default is to print a warning or the
fixed up value and return error code 2.
Also see -S|--skip-illegal to output an empty
line instead of leaving out the line altogether.
.TP
.B   \fB-S\fR, \fB--skip-illegal
Deprecated, use -E|--empty-mode.
.TP
.B   \fB-E\fR, \fB--empty-mode
Output empty lines as placeholder for illegal
input, i.e. parser errors or date/times that
cannot be subtracted.
.TP
.B   \fB-f\fR, \fB--format\fR=\fISTRING
Output format.  This can either be a specifier
string (similar to strftime()'s FMT) or the name
of a calendar.
.TP
.B   \fB-i\fR, \fB--input-format\fR=\fISTRING\fR...
Input format, can be used multiple times.
Each date/time will be passed to the input
format parsers in the order they are given, if a
date/time can be read successfully with a given
input format specifier string, that value will
be used.
.TP
.B   \fB-b\fR, \fB--base\fR=\fIDT
For underspecified input use DT as a fallback to
fill in missing fields.  Also used for ambiguous
format specifiers to position their range on the
absolute time line.
Must be a date/time in ISO8601 format.
If omitted defaults to the current date/time.
.TP
.B   \fB-e\fR, \fB--backslash-escapes
Enable interpretation of backslash escapes in the
output and input format specifier strings.
.TP
.B       \fB--from-locale\fR=\fILOCALE
Interpret dates on stdin or the command line as
coming from the locale LOCALE, this would only
affect month and weekday names as input formats
have to be specified explicitly.
.TP
.B       \fB--from-zone\fR=\fIZONE
Interpret dates on stdin or the command line as
coming from the time zone ZONE.
.SH FORMAT SPECS
.PP
Format specs in dateutils are similar to posix' strftime().
.PP
However, due to a broader range of supported calendars dateutils must
employ different rules.
.PP
Date specs:
.nf
  %a  The abbreviated weekday name
  %A  The full weekday name
  %_a The weekday name shortened to a single character (MTWRFAS)
  %b  The abbreviated month name
  %B  The full month name
  %_b The month name shortened to a single character (FGHJKMNQUVXZ)
  %c  The count of the weekday within the month (range 00 to 05)
  %C  The count of the weekday within the year (range 00 to 53)
  %d  The day of the month, 2 digits (range 00 to 31)
  %D  The day of the year, 3 digits (range 000 to 366)
  %F  Equivalent to %Y-%m-%d (ymd's canonical format)
  %g  ISO week date year without the century (range 00 to 99)
  %G  ISO week date year including the century
  %j  Equivalent to %D
  %m  The month in the current calendar (range 00 to 12)
  %Q  The quarter of the year (range Q1 to Q4)
  %q  The number of the quarter (range 01 to 04)
  %s  The number of seconds since the Epoch.
  %u  The weekday as number (range 01 to 07, Sunday being 07)
  %U  The week count,  day of week is Sun (range 00 to 53)
  %V  The ISO week count,  day of week is Mon (range 01 to 53)
  %w  The weekday as number (range 00 to 06, Sunday being 00)
  %W  The week count,  day of week is Mon (range 00 to 53)
  %y  The year without a century (range 00 to 99)
  %Y  The year including the century
  %_y The year shortened to a single digit
  %Z  The zone offset in hours and minutes (HH:MM) with
      a preceding sign (+ for offsets east of UTC, - for offsets
      west of UTC)
.fi
.PP
.nf
  %Od The day as roman numerals
  %Om The month as roman numerals
  %Oy The two digit year as roman numerals
  %OY The year including the century as roman numerals
.fi
.PP
.nf
  %rs In time systems whose Epoch is different from the unix Epoch, this
      selects the number of seconds since then.
  %rY In calendars with years that don't coincide with the Gregorian
      years, this selects the calendar's year.
.fi
.PP
.nf
  %dth  The day of the month as an ordinal number, 1st, 2nd, 3rd, etc.
  %mth  The month of the year as an ordinal number, 1st, 2nd, 3rd, etc.
.fi
.PP
.nf
  %db The business day of the month (since last month's ultimo)
  %dB Number of business days until this month's ultimo
.fi
.PP
Time specs:
.nf
  %H  The hour of the day using a 24h clock, 2 digits (range 00 to 23)
  %I  The hour of the day using a 12h clock, 2 digits (range 01 to 12)
  %M  The minute (range 00 to 59)
  %N  The nanoseconds (range 000000000 to 999999999)
  %p  The string AM or PM, noon is PM and midnight is AM.
  %P  Like %p but in lowercase
  %S  The  (range 00 to 60, 60 is for leap seconds)
  %T  Equivalent to %H:%M:%S
.fi
.PP
General specs:
.nf
  %n  A newline character
  %t  A tab character
  %%  A literal % character
.fi
.PP
Modifiers:
.nf
  %O  Modifier to turn decimal numbers into Roman numerals
  %r  Modifier to turn units into real units
  %0  Modifier to turn on zero prefixes
  %SPC  Modifier to turn on space prefixes
  %-  Modifier to turn off prefixes altogether
  th  Suffix, read and print ordinal numbers
  b   Suffix, treat days as business days
.fi
.PP
By design dates before 1601-01-01 are not supported.
.PP
For conformity here is a list of calendar designators and their
corresponding format string:
.nf
  ymd     %Y-%m-%d
  ymcw    %Y-%m-%c-%w
  ywd     %rY-W%V-%u
  bizda   %Y-%m-%db
  lilian     n/a
  ldn        n/a
  julian     n/a
  jdn        n/a
  matlab     n/a
  mdn        n/a
.fi
.PP
These designators can be used as output format string, moreover,
@code{lilian}/@code{ldn} and @code{julian}/@code{jdn} can also be used
as input format string.

.SH FORMAT SPECS FOR DURATIONS
.PP
Unlike time or absolute instants, durations are reference-free, i.e. the
reference instant is not part of the duration.  As a result durations
cannot be named, i.e. there is no naming scheme that applies to all
durations and all references unambiguously.
.PP
Consequently, none of the format specifiers for date/times makes sense
for durations in the literal sense.  However, to aid intuitive usage we
reused format specifiers when they represent integral values and a valid
unit for duration, as follows:
.PP
Date specs:
.nf
  %c  Equivalent to %w
  %d  Duration in days
  %F  Equivalent to %dd with no resorting to bigger units
  %m  Duration in months
  %w  Duration in weeks
  %y  Equivalent to %Y
  %Y  Duration in years
.fi
.PP
.nf
  %db Duration in business days
  %dB Equivalent to %db
.fi
.PP
Time specs:
.nf
  %H  Duration in hours
  %I  Equivalent to %H
  %M  Duration in minutes
  %S  Duration in seconds
  %T  Equivalent to %Ss without resorting to bigger units
.fi
.PP
.nf
  %rS Duration in real-life seconds, as in including leap seconds
  %rT Equivalent to %rSs without resorting to bigger units
.fi
.PP
General specs:
.nf
  %n  A newline character
  %t  A tab character
  %%  A literal % character
.fi
.PP
Modifiers:
.nf
  %r    Modifier to turn units into real units
  %0    Modifier to pad refined values with zeroes
  %SPC  Modifier to pad refined values with spaces
  b     Suffix, treat days as business days
.fi
.PP
.SH THE REFINEMENT RULE
.PP
Durations are somewhat ambiguous when it comes to representing them
through format specifiers.  Unlike format specifiers in point-in-time
representations duration specifiers can have an intra-line relationship.
.PP
So for instance a duration of 128 seconds might be presented through
"%S" as "128" but similarly through "%M:%S" as
"02:08" (read two minutes and 8 seconds).
.PP
There are several approaches to deal with this ambiguity.  The ddiff
tool will follow, what we call, the refinement rule.  That is,
regardless of the position of a format specifier, if it is a valid
/refinement/ of another specifier in the format string, then it
will only show the fractional value, i.e. the value in its natural range
with respect to the /refined/ specifier.
.PP
.nf
  %Y  possible refinements: %m, %w, %d
  %m  possible refinements: %w, %d
  %w  possible refinements: %d
  %d  possible refinements: %H, %M, %S
  %H  possible refinements: %M, %S
  %M  possible refinements: %S
.fi
.PP
The refinement alternatives are listed in order of precedence and they
are mutually exclusive.  I.e. it is not possible to express a duration
in months and hours without having a "%d" specifier as well.  On
the other hand in a chain of refinements inner elements are optional,
i.e. you can express a duration in weeks and hours because every day has
24 hours and hence there are 168 hours in a week.
.PP
In case of negative durations (the minuend is in the future relative to
the subtrahend) only the largest unit will carry the minus sign.
.PP
Using the refinement rule keeps the format string dead simple, there's
no need for operators or a full-blown language to distinguish the range
ambiguity, which then would have to be escaped because they could also
in theory be part of the literal characters of the format string,
resulting more often than not in command lines that are hard to craft
and even harder to understand later on (e.g. if used in shell scripts).
.PP
The refinement rule ingeniously covers the 99% case but, unlike other
approaches, there's no way to display two unrefined values in the
same format string, e.g. "'%w weeks (which is %d days)'".

.SH EXAMPLES
.PP
.nf
  $ ddiff 2012-03-02 2012-03-02
  0
  $
.fi
.PP
.nf
  $ ddiff 2012-03-02 2012-03-12
  10
  $
.fi
.PP
.nf
  $ ddiff 2012-03-02 2012-04-12
  41
  $
.fi
.PP
.nf
  $ ddiff 2012-03-12 2012-04-02
  21
  $
.fi
.PP
.nf
  $ ddiff 2012-04-02 2012-03-12
  -21
  $
.fi
.PP
.nf
  $ ddiff 2012-01-02 2012-02-29 -f '%dd'
  58d
  $
.fi
.PP
.nf
  $ ddiff 2012-01-02 2012-02-29 -f '%ww %dd'
  8w 2d
  $
.fi
.PP
.nf
  $ ddiff 10:00:00 10:00:00
  0s
  $
.fi
.PP
.nf
  $ ddiff 10:01:00 10:06:00
  300s
  $
.fi
.PP
.nf
  $ ddiff 10:06:00 10:01:00
  -300s
  $
.fi
.PP
.nf
  $ ddiff 10:01:00 11:03:10 -f '%S sec'
  3730 sec
  $
.fi
.PP
.nf
  $ ddiff 10:01:00 11:03:10 -f '%Mm %Ss'
  62m 10s
  $
.fi
.PP
.nf
  $ ddiff 10:01:00 11:03:10 -f '%H:%M:%S'
  1:2:10
  $
.fi
.PP
.nf
  $ ddiff 2012-03-02T10:04:00 2012-03-02T10:14:00
  600s
  $
.fi
.PP
.nf
  $ ddiff 2012-03-02T10:04:00 2012-03-02T10:14:00 -f '%M min'
  10 min
  $
.fi
.PP
.nf
  $ ddiff 2012-03-01T12:17:00 2012-03-02T14:00:00
  92580s
  $
.fi
.PP
.nf
  $ ddiff 2012-03-01T12:17:00 2012-03-02T14:00:00 -f '%d days and %S seconds'
  1 days and 6180 seconds
  $
.fi
.PP

.SH AUTHOR
Written by Sebastian Freundt <freundt@fresse.org>
.PP
.SH REPORTING BUGS
Report bugs to: https://github.com/hroptatyr/dateutils/issues
.PP



.SH "SEE ALSO"
The full documentation for
.B datediff
is maintained as a Texinfo manual.  If the
.B info
and
.B datediff
programs are properly installed at your site, the command
.IP
.B info (dateutils)datediff
.PP
should give you access to the complete manual.
.\" yuck.m4man ends here
