use strict;
my $str = 'act=abc aaa=zzz bbb zzz cc=ddd dd=aa bb cc';
my $regex = qr/ (?=[a-z]+=)/mp;
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