Date Seq

Easily create a sequence of dates.

Answer to a Stackoverflow question.

Reasoning

Bash is best written when leveraging pipes (|). It allows for easily composing programs.

Most of you are familiar with the seq command. We'll use this to compose a program that will create date sequences.

seq --help | head -n 3

Usage: seq [OPTION]... LAST
  or:  seq [OPTION]... FIRST LAST
  or:  seq [OPTION]... FIRST INCREMENT LAST

seq 3 # Does not contain the zero

1
2
3

seq 0 3 # Contains the zero

0
1
2
3

seq 0 4 12 # With a different increment than 1

0
4
8
12

seq -3 0 # From negative numbers till zero

-3
-2
-1
0

date-seq is a command that intends to leverage this command to create sequences of dates.

Usage

Dates from now till n days from now.

seq 0 3 | date-seq

zo 13 feb 2022 11:30:00 CET
ma 14 feb 2022 11:30:00 CET
di 15 feb 2022 11:30:00 CET
wo 16 feb 2022 11:30:00 CET

Iterate with an increment from now.

seq 0 4 12 | date-seq

zo 13 feb 2022 11:30:00 CET
do 17 feb 2022 11:30:00 CET
ma 21 feb 2022 11:30:00 CET
vr 25 feb 2022 11:30:00 CET

How about creating a sequence from a few increments from the past till now.

seq -3 0 | date-seq

do 10 feb 2022 11:30:00 CET
vr 11 feb 2022 11:30:00 CET
za 12 feb 2022 11:30:00 CET
zo 13 feb 2022 11:30:00 CET

seq doesn't give output when the FROM option is greater than the TILL.

seq 0 -1 # Does not write anything to STDOUT.

In the case we want to reverse the sequence of dates we can do three things.

seq -1  0 | tac | date-seq # firstly

seq -1  0 | date-seq | tac # secondly

seq  0  1 | date-seq '-%sdays' # thirdly

Create a sequence where each increment is a month. For this we change the template.

seq 0 3 | date-seq '+%smonth'

zo 13 feb 2022 11:30:00 CET
zo 13 mrt 2022 11:30:00 CET
wo 13 apr 2022 12:30:00 CEST
vr 13 mei 2022 12:30:00 CEST

The template is based on a combination of printf's %s string substitution and date's --date argument value. See printf and date manual pages for more information.

date-seq wraps the date command.

It takes date compatible options after the first template argument.

seq 0 3 | date-seq '-%smonth' +%b

feb
jan
dec
nov

In order to change the locale one simply configures it by using the date LANG environment variables.

seq 0 3 | LANG='en-US' date-seq '-%smonth' +%b

Feb
Jan
Dec
Nov

License

GPL-3.0