use strict;
my $str = 'sd<p><em>Hi [User</em></p>
<p><em>Tack för visat intresse.</em></p>
<p><em>Good luck!</em><em> </em></p>
<p><em>Sincerely</em></p>sd';
my $regex = qr/[^<>\s](?![^<>]*>)/mp;
my $subst = 'n';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html