How to generate a list of all dates in a range using the tools available in bash?
If you are on macOS, then date
works a bit differently from GNU date
. Here's a variant to Tom Fenech's date
invocation that supports both GNU and Darwin:
if [ $(uname) = 'Darwin' ]; then
d=$(date -j -v+1d -f %Y-%m-%d $d +%Y-%m-%d)
elif [ $(uname) = 'Linux' ]; then
d=$(date -I -d "$d + 1 day")
fi
If you have GNU date
, you could do use either a for
loop in any POSIX-compliant shell:
# with "for"
for i in {1..5}; do
# ISO 8601 (e.g. 2020-02-20) using -I
date -I -d "2014-06-28 +$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
.
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