Although both the subject and the description of the problem may suggest that he's after something like the code you suggest, I don't think he really wants to split his input into several different files. I think it's more reasonable to assume he's after something along the lines of:

#!/usr/bin/perl

use strict;
use warnings;

$\ = $, = "\n";
chomp(my $head=<>);

my ($last,@buffer);
while (<>) {
    chomp;
    my $time = (split)[0];
    if ( $time eq ($last ||= $time) ) {
        push @buffer, $_;
    } else {
        print $head, @buffer;
        ($last,@buffer)=($time,$_);
    }
}
print $head, @buffer;

__END__
[download]

Note that this assumes the input is ordered, which seems reasonable too, if you read the description carefully. Of course I do not claim it to be the cleanest or smartest way to do it, either.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.