while(<F>) {
    s/&/&amp;/g;
    s/</&lt;/g;
    s/>/&gt;/g;
    s!(https?://[-~@=_%;&/\+\.\?a-zA-Z0-9]+)!<a href="$1">$1</a>!g;
    s!([-_\+\.a-zA-Z0-9]+@[-_\+\.a-zA-Z0-9]+)!<a href="mailto:$1">$1<\/a>!g;
# then print $_, or whatever you want to do with it
}