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in reply to Generate all unique combinations of 1 and 0 using specified length of "0"-string and count of 1's

You can use a regular expression!!! 
my $length = 10;
my $ones = 4;

my $str = ("1" x $ones) . ("0" x ($length - $ones));

while(1) {
    print "$str\n";
    $str =~ s/^(0*)(1*)10/${2}${1}01/ or last
}

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