use strict;
my $str = '../app/code/community/Company/Module/Block/Adminhtml/Location/Grid.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Import.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Edit/Form.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Edit/Import.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Edit/Tabs.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Edit/Tab/Form.php
../app/code/community/Company/Module/Block/Adminhtml/Location/Edit/Tab/Import.php
../app/code/community/Company/Module/controllers/IndexController.php
../app/code/community/Company/Module/controllers/LocationController.php
../app/design/adminhtml/default/default/layout/pmodule.xml
../app/design/frontend/default/default/layout/pmodule.xml
../app/design/frontend/default/default/template/company/module/gmap.phtml';
my $regex = qr/^(.*?)\bdefault\b/mp;
my $subst = '\\1rwd';
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