use strict;
use warnings;
use Data::Dumper;

my @strings = qw(exception:tex exception:mex exception:mex asdf tex:exception:mex asdf exception:mex asdf asdf exception:mex);

foreach (1..4) {
    my @filtered = grep { pos = 0; /exception:/g && !/\Gtex/ } @strings;
    print Dumper(\@filtered);
}