not sure what you want, but remove the /g on /exception:/g. Also not sure what you mean with !/\Gtex/.

#!/usr/bin/perl -w
use strict;
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 { /exception:/ && !/mex/ } @strings;
    print Dumper(\@filtered);
}
__END__
prints:
$VAR1 = [
          'exception:tex'
        ];
$VAR1 = [
          'exception:tex'
        ];
$VAR1 = [
          'exception:tex'
        ];
$VAR1 = [
          'exception:tex'
        ];
[download]

if you just need the exception lines:

#!/usr/bin/perl -w
use strict;
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 { /exception:/ } @strings;
    print Dumper(\@filtered);
}
__END__
prints:
$VAR1 = [
          'exception:tex',
          'exception:mex',
          'exception:mex',
          'tex:exception:mex',
          'exception:mex',
          'exception:mex'
        ];
...3 more of same
[download]

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