use strict;
my $str = ' Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque sagittis semper ipsum at consectetur.
Fusce mauris " don\'t modify the space between quotes like this " massa, elementum id neque vel, facilisis ultrices enim. ';
my $regex = qr/^\s+|\s+$|\s+(?=\s)(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)/p;
my $subst = '';
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