Not sure about regexes, but counting frequencies means hashes.
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my $dict = '/var/lib/dict/words'; # YMMV
sub each_char_has_different_freq {
my ($r, $f) = @_;
keys %$r == keys %$f
}
sub frequencies_form_a_sequence {
my ($r) = @_;
keys %$r == grep $r->{$_}, 1 .. keys %$r
}
my @linenlessnesses;
open my $IN, '<', $dict or die $!;
while (<$IN>) {
chomp;
next if /\W/;
my %freq;
$freq{$_}++ for split //;
my %r = reverse %freq;
push @linenlessnesses, $_
if each_char_has_different_freq(\%r, \%freq)
&& frequencies_form_a_sequence(\%r);
}
say for sort { length $a <=> length $b } @linenlessnesses;
Interesting output (the longest words) on my machine:
deadheaded
evennesses
keennesses
peppertree
rememberer
restresses
sanenesses
sereneness
sleeveless
sussararas
susurruses
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,