And here you go. I &heart programming excercises like this. Reads files, outputs a reverse sorted list based on # of occurences. Note that some trigraphs may not be totally valid because of the s/\W//g;. for example, "this is a line.This is another one" will yield "lineThis" as a word to be trigraphed. This is trivial to fix, though :)

Update yes, it was.
I changed
s/ //g;
to s/\W//g; thanks, Albannach! (wave)

#
#
#
use strict;
my %symbol;
my %tri;
my @trikeys;
my $line;
my $ctr;
print "Processing file...\n";
while ($line = <>) {
    for (split /\W/,$line) {
        #discard all non-alpha. be *greedy*        
        s/\W//g;
        (length($_)>2) && $symbol{lc($_)}++;
    }
}

print "Collecting trigraphs...\n";
foreach (keys %symbol){
    for ($ctr=0; $ctr <= (length($_)-3);$ctr++) {
        $tri{lc(substr ($_,$ctr,3))}+= $symbol{$_};  
    }
}

@trikeys = sort {$tri{$b} <=> $tri{$a}} keys %tri;
print "Total Trigraphs : ",$#trikeys,"\n";
print "Trigraph\tCount\n";
foreach (@trikeys) {
    print "$_\t$tri{$_}\n"; 
}
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