Time::Piece (localtime/gmtime) calculation vs bash date - perl

Question

Have this bash script:
future="${1:-Dec 08 2017 22:00:00}"
t1=$(date -j -f "%b %d %Y %H:%M:%S" "$future" +%s) #using OS X
t0=$(date +%s)
echo "Current: $(date)"
echo "Future : $future"
echo "Diff : $(( $t1 - $t0 )) secs"
It prints:
Current: pi 8. december 2017 21:25:25 CET
Future : Dec 08 2017 22:00:00
Diff : 2075 secs
The result (diff) is correct.
Now trying to do the same using perl:
use strict;
use warnings;
use feature 'say';
use Time::Piece;
my $format = '%b %d %Y %H:%M:%S';
my $future = shift // 'Dec 08 2017 22:00:00';
say "Future: $future";
say "localtime: ", scalar localtime();
say "gmtime : ", scalar gmtime();
my $tf = Time::Piece->strptime($future, $format);
say 'localtime-diff : ', $tf-localtime();
say 'gmtime-diff : ', $tf-gmtime();
it prints
Future: Dec 08 2017 22:00:00
localtime: Fri Dec 8 21:27:45 2017 #correct
gmtime : Fri Dec 8 20:27:45 2017 #correct
localtime-diff : 5535 #incorrect (expecting 3600 secs less)
gmtime-diff : 5535 #ok
What is wrong? Mean, why it prints the same diff for the localtime and gmtime but the scalar localtime and scalar gmtime prints different (and correct) strings?
EDIT: So, the main question is: how to get the same result as in bash using perl?

Answer 1

Both localtime() and gmtime() return an object that represents now.
You are doing:
2017-12-08T22:00:00+00:00 - 2017-12-08T21:25:25+01:00 # $tf-localtime()
2017-12-08T22:00:00+00:00 - 2017-12-08T20:25:25+00:00 # $tf-gmtime()
It looks like you want to do
2017-12-08T22:00:00+01:00 - 2017-12-08T21:25:25+01:00
Using Time::Piece:
use Time::Piece qw( localtime );
my $future_str = 'Dec 08 2017 23:00:00';
my $format = '%b %d %Y %H:%M:%S';
my $future_dt = localtime->strptime($future_str, $format);
say $future_dt - localtime(); # 2241 (instead of 5841)
Using DateTime:
use DateTime::Format::Strptime qw( );
my $future_str = 'Dec 08 2017 23:00:00';
my $format = DateTime::Format::Strptime->new(
pattern => '%b %d %Y %H:%M:%S',
locale => 'en',
time_zone => 'local',
on_error => 'croak',
);
my $future_dt = $format->parse_datetime($future_str);
say $future_dt->epoch - time(); # 2241 (instead of 5841)