Thank you - that is much clearer. Here is your code with only the first regex changed and it now passes all the tests. HTH, Hippo.

#!/usr/bin/perl

use strict;
use warnings;
use Test::More;


my $regex = qr/pce_rx_n1\D*$/;

like( "pce_rx_n1", $regex, "Matching my regex" );
like( "pce_rx_n1_blah", $regex, "Matching my regex" );
#
#these fail because my $regex matches n1 and n10 and n13
#
unlike( "pce_rx_n13", $regex, "Not Matching my regex" );
unlike( "pce_rx_n10_blah", $regex, "Not Matching my regex" );

#fix the regex with the 
#zero look-ahead negative assertion
$regex = "/pce_rx_n1(?!\\d)/";

like( "pce_rx_n1", $regex, "Matching my regex" );
like( "pce_rx_n1_blah", $regex, "Matching my regex" );
unlike( "pce_rx_n12", $regex, "Not Matching my regex" );
unlike( "pce_rx_n10_blah", $regex, "Not Matching my regex" );

done_testing;
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