Dump the key value pairs in a hash

byrnejb has asked for the wisdom of the Perl Monks concerning the following question:

I am not a perl programmer. I do have to maintain a legacy perl application. Something has changed in the environment so that it no longer correctly reports the status of public key certificates. I need to discover what that change is and how to accommodate it. The critical piece of code appears to be:

sub genHTMLTableRow
  {
    my $self = shift;
    my $args = shift;
    my $e = shift;
    my $ser = $e->{serial};
    my $pem = $ser.'.html';

. . .
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What I wish to do for debugging purposes is to dump the actual contents of $self, $args, and $e. I tried the naive approach of using print "$self\n"; but that just gave me this:

CSP=HASH(0x800b1e060)
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I tried to use the map function

print map { "Key: $_ has Value:$self{$_}\n" } keys $self;
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I clearly do not understand the naming conventions of perl variables as this usage of map causes the error:

  Global symbol "%self" requires explicit package name (did you forget
+ to declare "my %self"?) at /root/bin/rcsp/blib/lib/CSP.pm line 861
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What is the perl way of displaying the contents of $self, $args, and $e?

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Re: Dump the key value pairs in a hash by choroba (Cardinal) on Oct 22, 2021 at 20:21 UTC
`$self` is a scalar variable, so it's not a hash, it's a reference to a hash. You need to dereference it to get the hash: `print map { "Key: $_ has Value:$self->{$_}\n" } keys %$self; # ~~ ~` [download] Or, use Data::Dumper: `use Data::Dumper; ... print Dumper($self);` [download] `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l] [select]
Re: Dump the key value pairs in a hash by haj (Vicar) on Oct 22, 2021 at 20:27 UTC
Well, yes, there's a rather easy fix. `$self` is a reference to the actual hash. You can convert ("dereference") it by writing `%$self` instead of `%self` (which is a variable of its own). However, a better approach would be to use one of Perl's modules for that. Data::Dumper is in Perl core, Data::Dump or Data::Print need to be installed using your package manager or CPAN and provide "nicer" output. For Data::Dumper, use: `use Data::Dumper; print Dumper $self; print Dumper $args; print Dumper $e;` [download] That should go a long way.	[reply] [d/l] [select]
Re: Dump the key value pairs in a hash by Anonymous Monk on Oct 22, 2021 at 20:19 UTC
Data::Dump from CPAN or Data::Dumper in the core	[reply]
Re: Dump the key value pairs in a hash by karlgoethebier (Abbot) on Oct 23, 2021 at 10:17 UTC
`use Data::Dump; sub genHTMLTableRow { my ($self, $args, $e ) = @_; # No triple shift dd for ($self, $args, $e); # It even rhymes! …; }` [download] Untested as I’m on a mobile device and in a hurry 🤪😎 BTW, `genHTMLTableRow` sounds like something that a class does. It cries downright for a role. See Class::Tiny as well as Role::Tiny for further inspiration. Regards, Karl Update: Fixed missing `$` before `self`. Thanks choroba. «The Crux of the Biscuit is the Apostrophe»	[reply] [d/l] [select]