Further to Re: Regex: finding all possible substrings: The approach shown in that reply will not handle overlapping matches of sub-strings that themselves contain other sub-strings, e.g., 'AAAA' containing 'AAA'.

Here's another approach that will handle such cases. It uses the  (*FAIL) verb, one of the Special Backtracking Control Verbs of 5.10+. Whether a pure-regex approach is faster than a (nested) loop/substring comparison approach is another question; Benchmark-ing alone will tell the tale. 

>perl -wMstrict -le
"my ($alts) =
   map  qr{ $_ }xms,
   join q{ | },
   qw(AAA AAC AAAAA AAAA ACA CCC CAA)
   ;
 print $alts;
 ;;
 my @strings = \qw(AAAAAT AAAACACA CAACAAA);
 my %counts  = count_em($alts, @strings);
 ;;
 print qq{for count_em};
 for my $k (sort keys %counts) {
   print qq{ in all strings: '$k' = $counts{$k}};
   }
 ;;
 sub count_em {
   my $alts = shift;
   ;;
   local our %count;
   use re 'eval';
   ${$_} =~ m{ ($alts) (?{ ++$count{$^N} }) (*FAIL) }xmsg
     for @_;
   return %count;
   }
"
(?^msx: AAA | AAC | AAAAA | AAAA | ACA | CCC | CAA )
for count_em
 in all strings: 'AAA' = 6
 in all strings: 'AAAA' = 3
 in all strings: 'AAAAA' = 1
 in all strings: 'AAC' = 2
 in all strings: 'ACA' = 3
 in all strings: 'CAA' = 2

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In reply to Re: Regex: finding all possible substrings by AnomalousMonk
in thread Regex: finding all possible substrings by ssc11008

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