... which is available as Algorithm::Loops::NextPermute().

And Algorithm::Loops offers another way to do this as well.

use strict;
use Algorithm::Loops qw( NestedLoops );
my $bits= 8;
my $ones= 5;
my $iter= NestedLoops(
    [   [ 0 .. $bits-1 ],
        ( sub {
            [ 1+$_[-1] .. $bits-1 ]
          }
        ) x ($ones-1),
    ],
);
my @ones;
while(  @ones= $iter->()  ) {
    my @bits= (0) x $bits;
    @bits[@ones]= (1) x $ones;
    print join '', @bits, $/;
}
[download]

Which is like

    my $bits= 8;
    for my $o0 ( 0 .. $bits-1 ) {
        for my $o1 ( 1+$o0 .. $bits-1 ) {
            for my $o2 ( 1+$o1 .. $bits-1 ) {
                for my $o3 ( 1+$o2 .. $bits-1 ) {
                    for my $o4 ( 1+$o3 .. $bits-1 ) {
                        my @bits= (0) x $bits;
                        @bits[$o0,$o1,$o2,$o3,$o4]= (1)x5;
                    }
                }
            }
        }
    }
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Except that the number of ones (and thus the number of nested loops) isn't hard-coded.

Update: You can also avoid some looping at the tail end by setting tight top limits:

use strict;
use Algorithm::Loops qw( NestedLoops );
my $bits= 8;
my $ones= 5;
my $iter= NestedLoops(
    [   [ 0 .. $bits - $ones ],
        map(
            {   # Need lexical for closure
                my $top= $bits - $ones + $_;
                sub {
                    [ 1+$_[-1] .. $top ]
                }
            }
            1 .. $ones-1,
        ),
    ],
);
my @ones;
while(  @ones= $iter->()  ) {
    my @bits= (0) x $bits;
    @bits[@ones]= (1) x $ones;
    print join '', @bits, $/;
}
[download]