#!/usr/bin/perl
use strict;

my $output = "";

open(FILE, "file.txt") || die "$!";
while(<FILE>)
{
  $output .= $_;
}
close FILE;

$output =~ s#(http://[^\!\"\£\$\^\*\(\)\{\}\[\]\;\:\'\@\,\<\> ]+)#\<a href="$1" target="_blank"\>$1\</a\>#gis;

print $output;