Perl string weirdness : equal strings being not equal? - string

Question

I am using Perl v5.16.2
I am using the Net::SMPP modules and it returns me some data.
If I show this data, I get this (simplified) :
$VAR1 = bless( {
'receipted_message_id' => '400002F6E09C61701222120140',
'30' => '400002F6E09C61701222120140'
}, 'Net::SMPP::PDU' );
Now, let's assume this data is in $pdu and I do this :
$message_id = $pdu->{30}; # or $pdu->{receipted_message_id}, same result
myfunction($message_id);
Then, I have myfunction defined as :
sub myfunction {
my $message_id = shift;
my $message_id_static = '400002F6E09C61701222120140';
print Dumper($message_id);
print Dumper($message_id_static);
print hexdump($message_id);
print hexdump($message_id_static);
if ($message_id eq $message_id_static)
{
print "match\n";
}
else
{
print "no match\n";
}
}
The output of the program is :
$VAR1 = '400002F6E09C61701222120140';
$VAR1 = '400002F6E09C61701222120140';
Data::Hexdumper: data length isn't an integer multiple of lines
so has been padded with NULLs at the end.
0x0000 : 34 30 30 30 30 32 46 36 45 30 39 43 36 31 37 30 : 400002F6E09C6170
0x0010 : 31 32 32 32 31 32 30 31 34 30 00 00 00 00 00 00 : 1222120140......
Data::Hexdumper: data length isn't an integer multiple of lines
so has been padded with NULLs at the end.
0x0000 : 34 30 30 30 30 32 46 36 45 30 39 43 36 31 37 30 : 400002F6E09C6170
0x0010 : 31 32 32 32 31 32 30 31 34 30 00 00 00 00 00 00 : 1222120140......
no match
Which doesn't make any sense to me... !
If I try to use $message_id to do a SQLite query, it fails miserably. If I use $message_id_static instead, it works perfectly.
So, is this a weird internal Perl bug, or am I missing something ?
This has been driving me nuts for hours...
EDIT :
Using the perl debugger, I get this :
DB<3> x $message_id_static
0 '400002F6E09C61701222120140'
DB<4> x $message_id
0 "400002F6E09C61701222120140\c#"
So at least I see there is a difference in the strings, but why isn't it seen by the hexdump, and what is that \c# ?
Thanks !

Answer 1

The \c# character is Ctrl-#, which is the ASCII NUL character at code point zero
You can't see it in your hexdump output because it is indistinguishable from the 00 padding at the end of the dump
If you set $Data::Dumper::Useqq = 1 then it will be visible in the output from print Dumper $message_id
You can remove it from the variable by using s/\0\z// or tr/\0//d, but you should really investigate why it is there in the first place