How to generate a list of all dates in a range using the tools available in bash?

Question

I want to download a bunch of files named with ISO-8601 dates. Is there a simple way to do this using bash+GNU coreutils? (Or some trick to make wget/curl to generate the list automatically, but I find that unlikely)

Similar to this question, but not restricted to weekdays: How to generate a range of nonweekend dates using tools available in bash?. I guess that there is a simpler way to do it without that restriction.

Also related to How to generate date range for random data on bash, but not restricted to a single year.

Answer 1

If you have GNU date, you could do use either a for loop in any POSIX-compliant shell:

# with "for" for i in {1..5}; do      # ISO 8601 (e.g. 2020-02-20) using -I     date -I -d "2014-06-28 +$i days"      # custom format using +     date +%Y/%m/%d -d "2014-06-28 +$i days" done 

or an until loop, this time using Bash's extended test [[:

# with "until" d="2014-06-29" until [[ $d > 2014-07-03 ]]; do      echo "$d"     d=$(date -I -d "$d + 1 day") done 

Note that non-ancient versions of sh will also do lexicographical comparison if you change the condition to [ "$d" \> 2014-07-03 ].

Output from either of those loops:

2014-06-29 2014-06-30 2014-07-01 2014-07-02 2014-07-03 

For a more portable way to do the same thing, you could use a Perl script:

use strict; use warnings; use Time::Piece; use Time::Seconds;     use File::Fetch;  my ($t, $end) = map { Time::Piece->strptime($_, "%Y-%m-%d") } @ARGV;   while ($t <= $end) {     my $url = "http://www.example.com/" . $t->strftime("%F") . ".log";     my $ff = File::Fetch->new( uri => $url );     my $where = $ff->fetch( to => '.' );  # download to current directory     $t += ONE_DAY; } 

Time::Piece, Time::Seconds and File::Fetch are all core modules. Use it like perl wget.pl 2014-06-29 2014-07-03.

Answer 2

Using GNU date and bash:

start=2014-12-29 end=2015-01-03 while ! [[ $start > $end ]]; do     echo $start     start=$(date -d "$start + 1 day" +%F) done 

2014-12-29 2014-12-30 2014-12-31 2015-01-01 2015-01-02 2015-01-03