Helloworld.txt

escaper.pl

#!/usr/bin/perl

undef $/;

$hostname = qr/[-a-z0-9]+(\.[-a-z0-9]+)*\.(com|edu|info)/;

$text = <>;
$text =~ s/&/&amp;/g;
$text =~ s/</&lt;/g;
$text =~ s/>/&gt;/g;
$text =~ s/^\s*$/<p>/mg;

$text =~ s{
	\b
	# capture the address to one
	(
		\w[-.\w]* #username
		\@
		 $hostname #hostname
	)
	\b
}{<a href='mailto:$1'>$1</a>}igx;

$text =~ s{
	\b(
		http:// $hostname  #hostname
		(
		   /[-a-z0-9_:\@&?=+,.!/~*'%\$]*
		)?
	)\b
}{
	<a href='$1'>$1</a>
}gix;

print $text;

Helloworld.txt

	 
	 
<h1>Hello world, foobar,</h1> 
<h2>test</h2> 	
[email protected]    		[email protected] 
http://hello.com
http://hello-aaaa.com

usage.md

perl escaper.pl helloworld