#!/usr/bin/env perl
use warnings;
use strict;

my $timestamp;
my $entryline;
my $timestamp_regex = qr/^#([[:digit:]]{10})$/;
my $exclusion_regex = qr/^(?:ls?|man|cat)\b/;
my $state = "begin";

while (<>) {
	if ($state eq "begin") {
		if (/$timestamp_regex/) {
			$timestamp = $_;
			$state = "readtimestamp";
		}
		else {
			print;
			$state = "printedline";
		}
	}
	elsif ($state eq "printedline") {
		if (/$timestamp_regex/) {
			$timestamp = $_;
			$state = "readtimestamp";
		}
		else {
			print;
			$state = "printedline";
		}
	}
	elsif ($state eq "readtimestamp") {
		if (/$timestamp_regex/ && $1 >= $timestamp) {
			$timestamp = $_;
			$state = "readtimestamp";
		}
		elsif (/$exclusion_regex/) {
			$entryline = $_;
			$state = "readentryline";
		}
		else {
			print $timestamp;
			print;
			$state = "printedline";
		}
	}
	elsif ($state eq "readentryline") {
		if (/$timestamp_regex/) {
			$entryline = "";
			$timestamp = $_;
			$state = "readtimestamp";
		}
		else {
			print $timestamp;
			print $entryline;
			print;
			$state = "printedline";
		}
	}
}

##</code><code>##

use warnings;
use strict;

my $exclre = qr/^(?:ls?|man|cat)\b/;

my @buf;
while (<>) {
	if (/^#\d+$/ || eof()) {
		push @buf, $_ if eof();
		if (@buf>2 || @buf==2 && $buf[1]!~$exclre) {
			print @buf;
		}
		@buf=();
	}
	push @buf, $_;
}

##</code><code>##

use warnings;
use strict;

my $exclre = qr/(?:ls?|man|cat)\b/;

$/ = "\n#";
while (<>) {
	s/\n#?\z//;
	print /\A#/?():'#', $_, "\n"
		unless /\A#?\d+\n$exclre(?!.*\n)/;
}