#!/usr/bin/perl 
use strict;
use warnings;
use Algorithm::Permute;

my $p = Algorithm::Permute->new(['a','b','c','d','e'], 3);

my @results;

while (my @res = $p->next) 
{
   push @results, [@res = sort @res]; # use a different sort for numbers
}

my %seen;
@results = map {!$seen{"@$_"}++? $_:() }@results; # remove duplicates!

print join ("+",@$_)."\n" for @results;

__END__
Prints: Again I sorted results in program editor
        because actual program probably doesn't need
        that feature.

a+b+c
a+b+d
a+b+e
a+c+d
a+c+e
a+d+e
b+c+d
b+c+e
b+d+e
c+d+e

The unsorted output for reference::
a+b+c
b+c+d
a+c+d
a+b+d
b+c+e
a+c+e
b+d+e
c+d+e
a+d+e
a+b+e