If your input sets get much bigger than about 18 elements, you will probably want to consider converting this to an iterator form:

#! perl -slw
use strict;

sub parts {
    my $n = shift;
    return [] unless @_;
    map {
        local @_ = @_;
        my $first = join '', splice @_, 0, $_;
        map {
            [ $first, @$_ ]
        } parts( $n, @_ );
    } 1 .. ( @_ < $n ? @_ : $n );
}

print join'|', @$_ for parts( 3, 'a'..'g' );

__DATA__
C:\test>982945.pl
a|b|c|d|e|f|g
a|b|c|d|e|fg
a|b|c|d|ef|g
a|b|c|d|efg
a|b|c|de|f|g
a|b|c|de|fg
a|b|c|def|g
a|b|cd|e|f|g
a|b|cd|e|fg
a|b|cd|ef|g
a|b|cd|efg
a|b|cde|f|g
a|b|cde|fg
a|bc|d|e|f|g
a|bc|d|e|fg
a|bc|d|ef|g
a|bc|d|efg
a|bc|de|f|g
a|bc|de|fg
a|bc|def|g
a|bcd|e|f|g
a|bcd|e|fg
a|bcd|ef|g
a|bcd|efg
ab|c|d|e|f|g
ab|c|d|e|fg
ab|c|d|ef|g
ab|c|d|efg
ab|c|de|f|g
ab|c|de|fg
ab|c|def|g
ab|cd|e|f|g
ab|cd|e|fg
ab|cd|ef|g
ab|cd|efg
ab|cde|f|g
ab|cde|fg
abc|d|e|f|g
abc|d|e|fg
abc|d|ef|g
abc|d|efg
abc|de|f|g
abc|de|fg
abc|def|g
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