use strict;
my $str = 'Key name = value';
my $regex = qr/(?: # Non capturing group 1
\G # Matches where the regex engine stops in the previous step
(\w+) # capture group 1: a regex word of 1+ chars
\h* # zero or more horizontal spaces (space, tabs)
(?: # Non capturing group 2
=\h* # literal '=' follower by zero or more hspaces
(\w+) # capture group 2: a regex word of 1+ chars
)? # make the non capturing group 2 optional
)+ # repeat the non capturing group 1, one or more/xp;
my $subst = '\\1\\2';
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