Another way to do this is with "match global". In this case, we say essentially "give me the sequences of digits found". What separates the digit sequences (i.e. numbers) doesn't matter. non-digit stuff gets skipped. This is a case of specifying what we want instead of specifying and splitting upon what we don't want.

#!/volume/perl/bin/perl
use warnings;
use strict;
use DateTime::Duration;

my $time = "01:00:01.004";

my @output_list = $time =~ /(\d+)/g;

print "@output_list\n";  # 01 00 01 004
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Update: Also, often in Perl, it is advantageous to assign meaningful names to components of a split or match global. It is rare to see something like $output_list[3] in my Perl code because the reader has to know what the heck the value at index 3 means.

#!/volume/perl/bin/perl
use warnings;
use strict;
use DateTime::Duration;

my $time = "01:00:01.004";

my  ($hour,$min,$sec,$ms) = $time =~ /(\d+)/g;

print "hour=$hour\n",
      "minutes=$min\n",
      "seconds=$sec\n",
      "milliseconds=$ms\n";
__END__

hour=01
minutes=00
seconds=01
milliseconds=004
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Update again:
another possibility if the intent is to "delete the milliseconds"

my $time = "01:00:01.004";

my ($no_ms) = $time =~ /([\d:]+)/; #any digit or colon

print "no milliseconds = $no_ms\n"; no milliseconds = 01:00:01
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There are many variations upon this theme. I think the above is more clear, but...

my $time = "01:00:01.004";
$time =~ s/\.\d+$//; #explictly delete the ending milli_seconds
print "time stripped ms = $time\n";
#time stripped ms = 01:00:01
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