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PROGRAM:

NAME

ddiff - Compute duration from DATE/TIME (the reference date/time) to the other

SYNOPSIS

ddiff [OPTION]... DATE/TIME [DATE/TIME]...

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).

Recognized OPTIONs:

-h, --help
Print help and exit

-V, --version
Print version and exit

-q, --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.

-f, --format=STRING
Output format. This can either be a specifier string (similar to strftime()'s FMT)
or the name of a calendar.

-i, --input-format=STRING...
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.

-e, --backslash-escapes
Enable interpretation of backslash escapes in the output and input format specifier
strings.

--from-zone=ZONE
Interpret dates on stdin or the command line as coming from the time zone ZONE.

FORMAT SPECS FOR DURATIONS

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.

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:

Date specs:
%c Equivalent to %w
%d Durations in days
%F Equivalent to %dd with no resorting to bigger units
%m Durations in months
%w Durations in weeks
%y Equivalent to %Y
%Y Durations in years

%db Duration in business days
%dB Equivalent to %db

Time specs:
%H Durations in hours
%I Equivalent to %H
%M Durations in minutes
%S Durations in seconds
%T Equivalent to %Ss without resorting to bigger units

%rS Durations in real-life seconds, as in including leap seconds
%rT Equivalent to %rSs without resoring to bigger units

General specs:
%n A newline character
%t A tab character
%% A literal % character

Modifiers:
%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

THE REFINEMENT RULE

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.

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).

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 @emph{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 @emph{refined} specifier.

%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

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.

In case of negative durations (the minuend is in the future relative to the subtrahend)
@emph{only} the largest unit will carry the minus sign.

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).

The refinement rule ingeniously covers the 99% case but, unlike other approaches, there's
@emph{no} way to display two unrefined values in the same format string, e.g. "'%w weeks
(which is %d days)'".

EXAMPLES

$ ddiff 2012-03-02 2012-03-02
0
$

$ ddiff 2012-03-02 2012-03-12
10
$

$ ddiff 2012-03-02 2012-04-12
41
$

$ ddiff 2012-03-12 2012-04-02
21
$

$ ddiff 2012-04-02 2012-03-12
-21
$

$ ddiff 2012-01-02 2012-02-29 -f '%dd'
58d
$

$ ddiff 2012-01-02 2012-02-29 -f '%ww %dd'
8w 2d
$

$ ddiff 10:00:00 10:00:00
0s
$

$ ddiff 10:01:00 10:06:00
300s
$

$ ddiff 10:06:00 10:01:00
-300s
$

$ ddiff 10:01:00 11:03:10 -f '%S sec'
3730 sec
$

$ ddiff 10:01:00 11:03:10 -f '%Mm %Ss'
62m 10s
$

$ ddiff 10:01:00 11:03:10 -f '%H:%M:%S'
1:2:10
$

$ ddiff 2012-03-02T10:04:00 2012-03-02T10:14:00
600s
$

$ ddiff 2012-03-02T10:04:00 2012-03-02T10:14:00 -f '%M min'
10 min
$

$ ddiff 2012-03-01T12:17:00 2012-03-02T14:00:00
92580s
$

$ ddiff 2012-03-01T12:17:00 2012-03-02T14:00:00 -f '%d days and %S seconds'
1 days and 6180 seconds
$

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