Using Data::Printer from the Perl debugger

ibm1620 has asked for the wisdom of the Perl Monks concerning the following question:

I set up to use Data::Printer from the debugger using these instructions. It successfully rebound the debugger's p() command, except that it prints the data twice:

File foo.pl

#!/usr/bin/env perl
use v5.36;

say "Here is ~/.perldb:\n";
say qx(cat ~/.perldb);

my @xx = (qw/a b c d e/);
push @xx, [ 1,2,3 ];

my $foo = 1; # set breakpoint here and issue p @xx

say 'Show result of p @xx when issued from within program';
use Data::Printer;
p @xx;
[download]

Debug session:

$ perl -d ./foo.pl

Loading DB routines from perl5db.pl version 1.73
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(./foo.pl:4):    say "Here is ~/.perldb:\n";
  DB<1> b 10
  DB<2> c
Here is ~/.perldb:

use DB::Pluggable;
DB::Pluggable->run_with_config( \'[DataPrinter]' );

main::(./foo.pl:10):    my $foo = 1; # use as breakpoint
  DB<2> p @xx
[
    [0] "a",
    [1] "b",
    [2] "c",
    [3] "d",
    [4] "e",
    [5] [
            [0] 1,
            [1] 2,
            [2] 3
        ]
]
[
    [0] "a",
    [1] "b",
    [2] "c",
    [3] "d",
    [4] "e",
    [5] [
            [0] 1,
            [1] 2,
            [2] 3
        ]
]

  DB<3> c
Show result of p @xx when issued from within program
[
    [0] "a",
    [1] "b",
    [2] "c",
    [3] "d",
    [4] "e",
    [5] [
            [0] 1,
            [1] 2,
            [2] 3
        ]
]
Debugged program terminated.  Use q to quit or R to restart,
[download]

(I get the same result when I remove the last 3 lines from foo.pl).

Any idea how to fix this?

Comment on Using Data::Printer from the Perl debugger Select or Download Code

Replies are listed 'Best First'.
Re: Using Data::Printer from the Perl debugger by LanX (Saint) on Feb 25, 2023 at 17:55 UTC
Well I'd say you have to file a big report with those two modules involved. DB::Pluggable and Data::Printer I have a hunch that your problem here is that the debugger prints the result of your command while you trigger an internal print too. If I were you I'd go with the approach to define an alias `px` FWIW I successfully patched perl5db in the past to use Data::Dump you can find the discussions in the archives here. HTH :) Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^2: Using Data::Printer from the Perl debugger by ibm1620 (Hermit) on Feb 25, 2023 at 21:00 UTC
Thanks! Interestingly, the documentation specifies putting this into .perldb: `$DB::alias{px} = 's/px/DB::px/'; sub px { my $expr = shift; require Data::Printer; print Data::Printer::p($expr); }` [download] Which causes $expr to be printed twice, once colorized, and once uncolorized, as one might expect. Changing that last line to `Data::Printer::p($expr);` [download] fixes it.	[reply] [d/l] [select]
Re^3: Using Data::Printer from the Perl debugger by LanX (Saint) on Feb 25, 2023 at 22:33 UTC
IMHO someone should file a bug report with both modules. I think one of the authors had the behavior of Data::Dump::pp() in mind which doesn't print by itself when called in a non void context. And the other one just copied the doc without testing. Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply]
Re^4: Using Data::Printer from the Perl debugger by ibm1620 (Hermit) on Feb 26, 2023 at 00:24 UTC
Re^5: Using Data::Printer from the Perl debugger by LanX (Saint) on Feb 26, 2023 at 00:48 UTC
Some notes below your chosen depth have not been shown here
Re^5: Using Data::Printer from the Perl debugger by JoseRijo (Novice) on Mar 06, 2023 at 16:40 UTC
Some notes below your chosen depth have not been shown here
Re^2: Using Data::Printer from the Perl debugger by ibm1620 (Hermit) on Mar 02, 2023 at 02:42 UTC
Using pure guesswork, I made one change to DB::Pluggable::Plugin::DataPrinter.pm: `sub initialize { no warnings 'once'; # $DB::alias{p} = 's/^/use Data::Printer; /; eval $cmd'; $DB::alias{p} = 's/^/use Data::Printer; /'; }` [download] Now the p command prints its argument only once. I inserted `print $cmd;` before `eval $cmd`, entered p $my_var in the debugger, and it printed "p $my_var". Apparently the eval was unnecessary. FWIW.	[reply] [d/l] [select]
Re^3: Using Data::Printer from the Perl debugger by LanX (Saint) on Mar 02, 2023 at 08:31 UTC
You are mangling internal `p` command and aliases, here are dragons. If I were you I'd stick with `px` Otherwise you need to look into the code of `perl5db.pl` Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^4: Using Data::Printer from the Perl debugger by ibm1620 (Hermit) on Mar 02, 2023 at 16:07 UTC
Re^5: Using Data::Printer from the Perl debugger by LanX (Saint) on Mar 02, 2023 at 16:37 UTC
Re: Using Data::Printer from the Perl debugger by kcott (Archbishop) on Feb 25, 2023 at 18:21 UTC
G'day ibm1620, I can replicate your results. I made a verbatim copy of `foo.pl` (including shebang and `v5.36`). I have the latest versions of `DB::Pluggable` (1.112001) & `Data::Printer` (1.001000). I get identical output to what you show for '`perl -d ./foo.pl`'. I also tried with `.perldb` code formatted as shown in DB::Pluggable - SYNOPSIS. The result was the same ("prints twice") except, of course, for: `DB<2> c Here is ~/.perldb: use DB::Pluggable; DB::Pluggable->run_with_config(\<<EOINI); [DataPrinter] EOINI main::(./foo.pl:10): my $foo = 1; # set breakpoint here and issue p + @xx` [download] "I get the same result when I remove the last 3 lines from foo.pl" My result starts the same but ends with: `DB<3> c Debugged program terminated. Use q to quit or R to restart,` [download] I don't see this as being related to "prints twice"; however, it might be worth checking that the code you posted is the same as what you're running. After removing 3 lines, my last statement is '`my $foo = 1;`'. — Ken	[reply] [d/l] [select]
Re: Using Data::Printer from the Perl debugger [troubleshooting suggestion - IGNORE] by kcott (Archbishop) on Feb 25, 2023 at 19:02 UTC
Oops! Sorry! Egg on face :-( `foo.pl` contains `use Data::Printer`. The output format, in the examples below, has nothing to do with `.perldb`'s contents or existence. I've stricken it all and, because it was quite long, put it in a spoiler. <Reveal this spoiler or all in this thread> — Ken	[reply] [d/l] [select]


P is for Practical
	PerlMonks