#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11112217
use warnings;
use List::Util qw( sum );

my @array = qw( 1 2 3 4 5 );

local $_ = "@array";
for my $possible ( 1 .. @array )
  {
  my $pattern = join '.+?', ('\b(\d+)\b') x $possible;
  local $" = '+';
  /$pattern(?{print "@{^CAPTURE} = ", sum(@{^CAPTURE}), "\n"})(*FAIL)/
+;
  }
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Outputs:

1 = 1
2 = 2
3 = 3
4 = 4
5 = 5
1+2 = 3
1+3 = 4
1+4 = 5
1+5 = 6
2+3 = 5
2+4 = 6
2+5 = 7
3+4 = 7
3+5 = 8
4+5 = 9
1+2+3 = 6
1+2+4 = 7
1+2+5 = 8
1+3+4 = 8
1+3+5 = 9
1+4+5 = 10
2+3+4 = 9
2+3+5 = 10
2+4+5 = 11
3+4+5 = 12
1+2+3+4 = 10
1+2+3+5 = 11
1+2+4+5 = 12
1+3+4+5 = 13
2+3+4+5 = 14
1+2+3+4+5 = 15
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