There's no function for this exactly that I know of, but it's trivial to get counts per character that you can use for this purpose:

my $string = '123456789012345';

my %counts ;

$counts{ $_ }++ for split //, $string;

foreach my $char ( keys %counts ){
    if( $counts{ $char } > 1 ){
        print "$char is not unique in $string\n";
    }else{
        print "$char is unique in $string\n";
    }
}
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