#!/usr/bin/perl
use strict;
use warnings;
use Date::Manip;

# I assume you do not want to use the underscore alternatively just add it
my $date = UnixDate(ParseDate("now"), "%Y-%m-%d %T");
print $date . "\n";

my $dt = `date +%F_%T`;
chomp $dt;

print $dt . "\n";
my $latest_dt;

my $dateAlternativeFormat = UnixDate(ParseDate("now"), "%a %b %d %T %Z %Y");

print "Starting run at: ".`date`;
print "Starting run at: ".$dateAlternativeFormat."\n";

__END__

$ perl test.pl
2018-04-25 11:28:18
2018-04-25_11:28:18
Starting run at: Wed Apr 25 11:28:18 CEST 2018
Starting run at: Wed Apr 25 11:28:18 CEST 2018