You also need a recursive solution that creates all combinations directly without the need of filtering duplicates:

use strict;
use warnings;

my $input  = 'ABC---';

sub insert {
  my( $sofar, $chars, $dashes ) = @_;
  print "$sofar\n" and return unless @$chars or @$dashes;
  insert( $sofar . $$chars[0],  [ @$chars[ 1..@$chars-1] ],   [ @$dash
+es ] ) if @$chars;
  insert( $sofar . $$dashes[0], [ @$chars ], [ @$dashes[ 1..@$dashes-1
+ ] ] ) if @$dashes;
}

insert( '', [ $input =~ /[^-]/g ], [ $input =~ /-/g ] );
[download]

UPDATE: operating on strings rather than arrays is even simpler:

use strict;
use warnings;

my $input  = 'ABC---';

sub insert {
  my( $sofar, $chars, $dashes ) = @_;
  print "$sofar\n" and return unless $chars or $dashes;
  insert( $sofar . substr( $chars, 0, 1),  substr( $chars, 1 ), $dashe
+s ) if $chars;
  insert( $sofar . substr( $dashes, 0, 1), $chars, substr( $dashes, 1)
+  ) if $dashes;
}

insert( '', $1, $2 ) if $input =~ /^([^-]+)(-+)$/;
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.