shellDatediff

Calculate time differences with Ksh, Bash and Zsh built-ins.

The project contains a small shell library to calculate elapsed time between two dates in various time units and some extra functions.

Results are delivered in different units taking into account all time units (compound time range), or as a fractional single time unit.

The script warps GNU/BSD C-code date programme to process input date strings in various formats (main function), otherwise input must be ISO-8601 or UNIX times.

Extensively tested, see testing scripts, notes, and man page.

✨ Features

• Defaults to standard ISO-8601 date input, or UNIX times
• Date offset aware, heeds environment $TZ
• Check whether year is leap
• Check moon / lunar phases
• Check Easter, Carnaval, and Corpus Christi dates
• Check for next Friday the 13th

Usage Examples

Time elapsed from April 15, 2008 to now

% datediff.sh 2008-01-15
DATES-
2008-01-15T00:00:00-02:00       1200362400
2023-02-10T02:35:50-03:00       1676007350
RANGES
15Y 00M 03W 05D  03h 35m 50s
15.1 years | 345.8 months | 786.4 weeks | 5505.1 days | 132123.6 hours | 7927415.8 mins | 475644950 secs

Check when next Friday the 13th is

% datediff.sh -F Fri 13
Fri, 13 Oct 2023 is  245 days away

Obs: set -FF to get the next 10 dates.

Check whether year 2023 is leap

% datediff.sh -l 2023
not leap year -- 2023

Obs: exit code 1 if not leap year.

Generate the lunar phase calendar for February, 20023

% datediff.sh -m 2023-02
2023-02-01  First Quarter
2023-02-02  Waxing Gibbous
2023-02-06  Full Moon
2023-02-09  Waning Gibbous
2023-02-13  Last Quarter
2023-02-17  Waning Crescent
2023-02-20  New Moon
2023-02-24  Waxing Crescent
2023-02-28  First Quarter

Generate dates for 2023 Carnaval, Easter (western church) and Corpus Christi dates

% datediff.sh -ee 2023
  Carnaval          Easter      CorpusChristi
2023-02-21      2023-04-09      2023-06-08

Obs: set multiple years to get a nice TSV-formatted output.

Requirements

• Ksh93, Bash or Zsh
• GNU/BSD/AST/Busybox date (optional)
• Bc (optional)

Help

Please, check script help page with datediff.sh -h.

See Also

• C-code dateutils/datediff, Hroptatyr, http://www.fresse.org/dateutils/.
• Python PDD, Jarun, https://github.com/jarun/pdd.
• AST date, see elapsed time option -E, https://github.com/att/ast.
• GNU units, https://www.gnu.org/software/units/.
• ``Calendrical calculation'', Dershowitz and Reingold, 1990, http://www.cs.tau.ac.il/~nachum/papers/cc-paper.pdf.

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