$ perl -e '
    use 5.010;
    use strict;
    use warnings;

    my $av_tmp_LINE = "Jun  3 23:20:05 f42252s5 postfix/pickup[204714]: E1E63A045C: uid=33 from=<www-data>";
    say "BEFORE: $av_tmp_LINE";
    $av_tmp_LINE =~ s/([&<>])/char_to_entity($1)/eg;
    say "AFTER:  $av_tmp_LINE";
    my $av_tmp_STRING = "Logfile: " . "<strong>" . q{$av_obj_TMP->{input}} . "</strong>" . " " . $av_tmp_LINE;
    say "\$av_tmp_STRING[$av_tmp_STRING]";

    sub char_to_entity {
        my ($char) = @_;
        state $entity_for = {qw{& &amp; < &lt; > &gt;}};
        return $entity_for->{$char};
    }
'
BEFORE: Jun  3 23:20:05 f42252s5 postfix/pickup[204714]: E1E63A045C: uid=33 from=<www-data>
AFTER:  Jun  3 23:20:05 f42252s5 postfix/pickup[204714]: E1E63A045C: uid=33 from=&lt;www-data&gt;
$av_tmp_STRING[Logfile: <strong>$av_obj_TMP->{input}</strong> Jun  3 23:20:05 f42252s5 postfix/pickup[204714]: E1E63A045C: uid=33 from=&lt;www-data&gt;]