You could also do something like: 
sub mylineOK {
  my ($line) = @_;
  my @ebase = ("A","T");
  my $limit = 15;

  for ( @ebase ) {
    my $cnt = ( $line =~ s/$_//g );
    return 0 if ( $cnt >= $limit );
  }
  return 1;
}

[download]
Which will just count the number of times the ebase is stripped from the line.

Update:

All of these return the correct answer (in my very limited dataset). Here are some benchmarks. 
              Rate  Original    Moritz         Tr         m     Strip 
+ExplicitTr
Original    87.3/s        --      -95%       -97%      -99%      -99% 
+     -100%
Moritz      1613/s     1748%        --       -50%      -74%      -81% 
+      -98%
Tr          3226/s     3596%      100%         --      -48%      -62% 
+      -96%
m           6250/s     7060%      288%        94%        --      -27% 
+      -92%
Strip       8571/s     9720%      431%       166%       37%        -- 
+      -89%
ExplicitTr 75000/s    85825%     4550%      2225%     1100%      775% 
+        --

[download]
Note that explicit tr uses a hardcoded "A" and "T" in place of a variable. (i.e. tr/A/A/ and tr/T/T/) The eval is what kills the performance.

In reply to Re: searching characters by Transient
in thread searching characters by Anonymous Monk

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