Don't use character class, use alternations and anchoring in case the string is longer than one character: =~ m/^(?:7|8|9)$/. Don't forget to use quotemeta on the strings.

sub dequote {
   local $_ = (@_ ? $_[0] : $_);
   s/^'//;
   s/'$//;
   s/\\(.)/$1/s;
   return $_;
}

my $list = join '|',
           map quotemeta,
           map dequote,
           @parts;

print("=~ m/^(?:$list)\$/");
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How do you extract the parts? Well, that's quite hard to do right using regexp. You should write a parser.