Perl Hashref Substitutions - perl

Question

I'm using DBI to connect to Sybase to grab records in a hash_ref element. The DBI::Sybase driver has a nasty habit of returning records with trailing characters, specifically \x00 in my case. I'm trying to write a function to clean this up for all elements in the hashref, the code I have below does the trick, but I can't find a way to make it leaner, and I know there is away to do this better:
#!/usr/bin/perl
my $dbh = DBI->connect('dbi:Sybase:...');
my $sql = qq {SELECT * FROM table WHERE age > 18;};
my $qry = $dbh->selectall_hashref($sql, 'Name');
foreach my $val(values %$qry) {
$qry->{$val} =~ s/\x00//g;
}
foreach my $key(keys %$qry) {
$qry->{$key} =~ s/\x00//g;
foreach my $val1(keys %{$qry->{$key}}) {
$qry->{$key}->{$val1} =~ s/\x00//g;
}
foreach my $key1(keys %{$qry->{$key}}) {
$qry->{$key}->{$key1} =~ s/\x00//g;
}

Answer 1

While I think that a regex substitution is not exactly an ideal solution (seems like it should be fixed properly instead), here's a handy way to solve it with chomp.
use Data::Dumper;
my %a = (
foo => {
a => "foo\x00",
b => "foo\x00"
},
bar => {
c => "foo\x00",
d => "foo\x00"
},
baz => {
a => "foo\x00",
a => "foo\x00"
}
);
$Data::Dumper::Useqq=1;
print Dumper \%a;
{
local $/ = "\x00";
chomp %$_ for values %a;
}
print Dumper \%a;
chomp will remove a single trailing value equal to whatever the input record separator $/ is set to. When used on a hash, it will chomp the values.
As you will note, we do not need to use the values directly, as they are aliased. Note also the use of a block around the local $/ statement to restrict its scope.
For a more manageable solution, it's probably best to make a subroutine, called recursively. I used chomp again here, but you can just as easily skip that and use s/\x00//g. Or tr/\x00//d, which basically does the same thing. chomp is only safer in that it only removes characters from the end of the string, like s/\x00$// would.
strip_null(\%a);
print Dumper \%a;
sub strip_null {
local $/ = "\x00";
my $ref = shift;
for (values %$ref) {
if (ref eq 'HASH') {
strip_null($_); # recursive strip
} else {
chomp;
}
}
}

Answer 2

First your code:
foreach my $val(values %$qry) {
$qry->{$val} =~ s/\x00//g;
# here you are using a value as if it was a key
}
foreach my $key(keys %$qry) {
$qry->{$key} =~ s/\x00//g;
foreach my $val1(keys %{$qry->{$key}}) {
$qry->{$key}->{$val1} =~ s/\x00//g;
}
foreach my $key1(keys %{$qry->{$key}}) {
$qry->{$key}->{$key1} =~ s/\x00//g;
}
# and this does the same thing twice...
what you should do is:
foreach my $x (values %$qry) {
foreach my $y (ref $x eq 'HASH' ? values %$x : $x) {
$y =~ s/(?:\x00)+$//
}
}
which will clean up only ending nulls in the values of two levels of the hash.
the body of the loop could also be written as:
if (ref $x eq 'HASH') {
foreach my $y (values %$x) {
$y =~ s/(?:\x00)+$//
}
}
else {
$x =~ s/(?:\x00)+$//
}
But that forces you to write the substitution twice, and you shouldn't repeat yourself.
Or if you really want to reduce the code, using the implicit $_ variable works well:
for (values %$qry) {
s/(?:\x00)+$// for ref eq 'HASH' ? values %$_ : $_
}