If the above routine is run on certain *nixes (but not Windows), each call to the above subroutine will print out a "Use of uninitialized value in subroutine" warning along with the dump.

This is apparently due to a bug in Devel::Peek::Dump (see my note below). To eliminate the warning on those systems you will need to make the following change to the subroutine suggested by repellent:

Read more... (833 Bytes)

Best beth

As repellent has pointed out, the way to get Devel::Peek::Dump to write to a string is to redirect STDERR to a string. However, if you are running on certain *nixes (Debian-Etch/Perl 5.8.8 and possibly others), the first time you call Devel::Peek::Dump whilst STDERR is redirected to a string, you may see a "Use of uninitialized value in subroutine" warning. This warning does not seem to appear on Windows (so saith ikegami who tried it on Windows for me).

As near as we could tell, this a bug in Devel::Peek::Dump. It has been reported and ticketed as bug 63498. The bug is rated low severity, so you may have to wait a while before this particular annoyance goes away.

Best, beth

Update: more clearly identified systems with potential problems

Could it be that the string variable just has to be initialized to an empty string?


use strict;
use warnings;

use Devel::Peek;

# initialized here
my $sOut = "";

close(STDERR);
open(STDERR, ">", \$sOut) or die "Can't redirect STDERR to \\\$sOut";
my $s=1;

Devel::Peek::Dump $s;
Devel::Peek::Dump $s;
print "<<$sOut>>\n";
[download]

Apparently so! I thought I made sure of that.

Great catch! But here's a wrinkle. Other common uses of STDERR redirected to string, namely print, do not require the string variable to be initialized. For example:

use strict;
use warnings;

my $sOut;
close(STDERR);
open(STDERR, ">", \$sOut)
  or die "Can't redirect STDERR to \\\$sOut";
print STDERR "Hello World!\n";
print $sOut;
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happily outputs "Hello World" without generating a warning (at least on my system). Somehow, I don't think the Devel::Peek::Dump behavior qualifies as Inconsistent for the sake of convenience :-)

Best, beth

Hmmm... I don't see the bug on my Linux box:


$ cat /etc/redhat-release 
Red Hat Enterprise Linux WS release 4 (Nahant Update 4)

$ perl -v

This is perl, v5.8.5 built for i686-linux-thread-multi

Copyright 1987-2004, Larry Wall

Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using `man perl' or `perldoc perl'.  If you have access to
+ the
Internet, point your browser at http://www.perl.com/, the Perl Home Pa
+ge.
[download]


UPDATE: I was wrong. My use warnings; was commented out. Bug confirmed on my platform.

Dropping in after a reference to this was posted on the perl5 mailing list.

The redirection to STDERR was exactly the reason why I wrote Data::Peek

   use Data::Peek;
   my %hash = ( boo => [ 1..3 ], blah => "ab\nc\x{20ac}" );
   my $dump;
   open my $fh, ">", \$dump;
   DDump_IO ($fh, \%hash, 6);
   close $fh;
   print $dump;
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This uses perl internals to dump data structures, instead of using perl code to traverse and dump.

SV = RV(0x8804c8) at 0x8804b8
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x880530
    SV = PVHV(0x866db0) at 0x880530
      REFCNT = 2
      FLAGS = (PADMY,SHAREKEYS)
      ARRAY = 0x86ef70  (0:7, 2:1)
      hash quality = 62.5%
      KEYS = 2
      FILL = 1
      MAX = 7
      RITER = -1
      EITER = 0x0
        Elt "blah" HASH = 0x4566b599
        SV = PV(0x85a098) at 0x8804a0
          REFCNT = 1
          FLAGS = (POK,pPOK,UTF8)
          PV = 0x86aa10 "ab\nc\342\202\254"\0 [UTF8 "ab\nc\x{20ac}"]
          CUR = 7
          LEN = 8
        Elt "boo" HASH = 0x73a487c9
        SV = RV(0x85c150) at 0x85c140
          REFCNT = 1
          FLAGS = (ROK)
          RV = 0x85c2f0
            SV = PVAV(0x85d490) at 0x85c2f0
              REFCNT = 1
              FLAGS = ()
              ARRAY = 0x86e970
              FILL = 2
              MAX = 2
              ARYLEN = 0x0
              FLAGS = (REAL)
                Elt No. 0
                SV = IV(0x85c4b0) at 0x85c4b8
                  REFCNT = 1
                  FLAGS = (IOK,pIOK)
                  IV = 1
                Elt No. 1
                SV = IV(0x880588) at 0x880590
                  REFCNT = 1
                  FLAGS = (IOK,pIOK)
                  IV = 2
                Elt No. 2
                SV = IV(0x880570) at 0x880578
                  REFCNT = 1
                  FLAGS = (IOK,pIOK)
                  IV = 3
[download]