use strict;
my $str = '1. http://www.example.com/myplan/mp/public/pl_be?Id=543543×tamp=06280435435
2. http://www.example.com/course/df/public/pl_de?Id=454354×tamp=0628031746
3. http://www.example.com/book/rg/public/pl_fo?Id=4445577×tamp=0628031734
4. http://www.example.com/trip/tr/public/pl_ds?Id=454354×tamp=06280314546
5. http://www.example.com/trip/tr/public/pl_ds';
my $regex = qr/(.*\/)[^?]*(?:(\?[^&]*).*)?/mp;
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