Uninitialized value in concatenation (.) or string?

jbush82 has asked for the wisdom of the Perl Monks concerning the following question:

I'm working on writing an MD5 hash scanner (searches for files on a system, if it finds a file that matches a filename of a known bad, does and MD5 on it and compares to known bad files MD5), and I've got it working up to the point of identifying the files on a system that match in my list of bad files (I think), but when I try to take the match data and put it into a multi-dimensional array, it seems to not be working.

If you'd like to give it a go up to this point, you need psexec (http://www.microsoft.com/technet/sysinternals/security/psexec.mspx) and also replace the IP address 1.2.3.4 in the script to the IP of the system you are currently on (need admin rights to do the scan). Any advice would be appreciated.

#!C:\perl\bin\perl.ex#!C:\perl\bin\perl.exe
use strict;

my @fileinfo;
my @sysfiles;
my $i = 0;
my $md5sum;
my $filename;
my $md5data;
my @md5info;
my @md5filename;

open(FILE, "knownbad.txt") or die("Unable to open file");
my @knownbad = <FILE>;
close(FILE);

my $k = 0;
foreach $md5data (@knownbad) {
  chop($md5data);
  ($filename, $md5sum) = split(/\,/, $md5data);
  $md5info[$k] = [$filename, $md5sum];
  $md5filename[$k] = $filename;
  $k++;
}

open FILES, "psexec.exe -n 2 \\\\1.2.3.4 cmd.exe \/C dir C\:\\ \/S \/B
+ |" or die;
while ( <FILES> )
{
  my $dir;
  my $file;
  ( $dir, $file ) = m/(.*)[\\\/](.+)/ ? ( $1, $2 ) : ( undef, $_ ); 
#  print "$file is in the directory $dir\n";
  $fileinfo[$i] = [$file, $dir];
  $sysfiles[$i] = $file;
  $i++;
}
close FILES;

sleep 5;

my $filecount = (scalar (@fileinfo)) - 1;
my $hashcount = (scalar (@md5info)) - 1;
my $refarray1 = $fileinfo[$filecount];
print "File: $refarray1}[0] --- Directory: ${$refarray1}[1]]\n";
my $refarray2 = $md5info[$hashcount];

my @isect_list;
my %isect = ();
map { $isect{$_} = 1 } @md5filename;
@isect_list = grep { $isect{$_} } @sysfiles;
my @uniq = sort keys %{ { map { $_, 1 } @isect_list } }; 

my @matchedfiles;
my $intersect;

foreach $intersect (@uniq) {
  my $c=0;
  while ($c <= $filecount){
    $refarray1 = $fileinfo[$c];
    if (${$refarray1}[0] eq $intersect) {
      print "File: ${$refarray1}[0] in directory ${$refarray1}[1]\n";
      push(@{$matchedfiles[$c]}, [${$refarray1}[0], ${$refarray1}[1]])
+;
    }
    $c++;
  }
}

print "\n\n";
my $refarray3 = $matchedfiles[5];
print "it's not defined!\n" unless defined(${$refarray3}[0]);
print "it's not defined!\n" unless defined(${$refarray3}[1]);
print "File: ${$refarray3}[0] in directory ${$refarray3}[1]\n";
[download]

Comment on Uninitialized value in concatenation (.) or string? Download Code

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Re: Uninitialized value in concatenation (.) or string? by pc88mxer (Vicar) on May 09, 2008 at 15:38 UTC
Is this where (if you uncommented the `print` statement) you are getting the "Uninitialized value in concatenation..." error: `( $dir, $file ) = m/(.*)[\\\/](.+)/ ? ( $1, $2 ) : ( undef, $_ ); # print "$file is in the directory $dir\n"; $fileinfo[$i] = [$file, $dir];` [download] If so, it's probably because `$dir` is getting set to `undef`, and then you are using it in string interpolation in the `print` statement. Also, later that `undef` value could be causing problems in this code fragment: `$refarray1 = $fileinfo[$c]; if (${$refarray1}[0] eq $intersect) { print "File: ${$refarray1}[0] in directory ${$refarray1}[1]\n"; $matchedfiles[$i] = [${$refarray1}[0], ${$refarray1}[1]]; }` [download] The expression `${$refarray1}[1]` refers to the `dir` component of your fileinfo structure, so if it is `undef`, the `print` statement in this fragment will also generate the same error message. Also, don't you want to increment `$i` in this loop? `$matchedfiles[$i++] = [${$refarray1}[0], ${$refarray1}[1]];` [download] In general it's easier to use `push`: `push(@matchedfiles, [ ... ]);` Update: Here are some style pointers that might make things a little cleaner. 1) Read the md5 info into a hash: `my %md5_of_known_bad; foreach $md5data (@knownbad) { ... $md5_known_bad{$filename} = $md5hash; }` [download] This serves two purposes: it stores the md5hash of a known bad file and it also can be used to determine if a file is a bad file by using `exists`: `if (exists $md5_of_known_bad{$filename}) { # $filename is a known bad }` [download] 2) Your intersection logic can then be simplified to: `my @uniq; @uniq = grep { exists $md5_of_known_bad{$_} } @sysfiles;` [download]	[reply] [d/l] [select]
Re^2: Uninitialized value in concatenation (.) or string? by jbush82 (Novice) on May 09, 2008 at 16:29 UTC
I just commented out the print statement to speed up the scan of the remote system (outputting slows it down a lot). I get the error on line 71 `Use of uninitialized value in concatenation (.) or string at nfse.pl line 71.` `69 print "\n\n"; 70 my $refarray3 = $matchedfiles[5]; 71 print "File: ${$refarray3}[0] in directory ${$refarray3}[1]\n";` [download] Also, don't you want to increment $i in this loop? `$matchedfiles[$i++] = [${$refarray1}[0], ${$refarray1}[1]];` Actually, I replaced $i with $c and just missed that spot when I did it. Ran the script again and I am of course having the same problem. In general it's easier to use push: push(@matchedfiles, ... ); I attempted this using `push($matchedfiles[$c], [${$refarray1}[0], ${$refarray1}[1]]);`, but I received the message: `D:\Documents\network file scanner\enhanced>perl -w nfse.pl Type of arg 1 to push must be array (not array element) at nfse.pl lin +e 63, near "])" Execution of nfse.pl aborted due to compilation errors.` [download] Thanks for your response. It is going to take me some time to figure out some of your recommendations. I'll post back once I've gone through it and hopefully got it going.	[reply] [d/l] [select]
Re^3: Uninitialized value in concatenation (.) or string? by pc88mxer (Vicar) on May 09, 2008 at 16:57 UTC
Check the value of `${$refarray3}[1]` for being `undef`: `print "it's not defined!\n" unless defined(${$refarray3}[1]);` [download] If it's `undef`, it's because of your assignment of `undef` to `$dir` back in the `while (<FILES>) {...}` loop. Perhaps you can use the empty string there instead. Also, if you want `$matchedfiles[$c]` to be list of files, you need to use this syntax: `push(@{$matchedfiles[$c]}, [...]);` [download] This makes `$matchedfiles[$c]` an array ref (i.e. `@matchedfiles` is an array of array refs.)	[reply] [d/l] [select]
Re^4: Uninitialized value in concatenation (.) or string? by jbush82 (Novice) on May 09, 2008 at 17:22 UTC
Re^5: Uninitialized value in concatenation (.) or string? by pc88mxer (Vicar) on May 09, 2008 at 17:54 UTC
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Re: Uninitialized value in concatenation (.) or string? by starbolin (Hermit) on May 10, 2008 at 06:29 UTC
This code: `push(@{$matchedfiles[$c]}, [ ... ]);` Is incorrect, it's usually a bad idea to use the index from one array to index into another array. $c holds the position in your fileinfo array but $matchedfiles[$c] is not defined yet. The error is compounded when you use $matchedfiles[$c] as an array reference as perl will automatically cause that element to spring to life ( and everything below it ) even if that element was not previously defined. This is called 'autovivification' and can be useful; but in this case is merely a troublesome side-effect of using an undefined reference. s//----->\t/;$~="JAPH";s//\r<$~~/;{s\|~$~-\|-~$~\|\|\|s \|-$~~\|$~~-\|\|\|s,<$~~,<~$~,,s,~$~>,$~~>,, $\|=1,select$,,$,,$,,1e-1;print;redo}	[reply] [d/l]
Re^2: Uninitialized value in concatenation (.) or string? by pc88mxer (Vicar) on May 10, 2008 at 07:10 UTC
starbolin writes: This code: `push(@{$matchedfiles[$c]}, [ ... ]);` Is incorrect. ... But I don't see a problem with auto-vivification in this case. Consider this test code: `use Data::Dumper; my @m; my $c; $c = 3; push(@{$m[$c]}, [ 'foo' ]); $c = 2; push(@{$m[$c]}, [ 'bar' ]); print Dumper(\@m), "\n"; for (0..3) { print "length of m[$_] = ", scalar(@{$m[$_]}), "\n"; }` [download] The first `push` not only creates `$m[3]` as an array ref, but also sets `$m[0]`, `$m[1]` and `$m[2]` to `undef`. The second `push` changes `$m[2]` from `undef` to a new array ref. The last `for` loop shows that `undef` is basically indistinguishable from `[]`, i.e. a reference to an empty array.	[reply] [d/l] [select]
Re^3: Uninitialized value in concatenation (.) or string? by starbolin (Hermit) on May 10, 2008 at 18:12 UTC
I didn't say auto-vivification was the problem. I said that using undefined references was his problem. Auto-vivification is saving his butt. He should be using a hash here. Trying to emulate a hash by using a sparse matrix is difficult, error prone and wrong. In general the code is very poor; the OP uses map when foreach would do, he uses foreach when map or grep is called for, he iterates over an array to create a hash when he could have hashed the data to begin with, he has multiple arrays holding the same data, he uses push when a hash is called for and he uses indexing where a push would serve. Arguing over auto-vivification is akin to rearranging the deck chairs while the ship is sinking. s//----->\t/;$~="JAPH";s//\r<$~~/;{s\|~$~-\|-~$~\|\|\|s \|-$~~\|$~~-\|\|\|s,<$~~,<~$~,,s,~$~>,$~~>,, $\|=1,select$,,$,,$,,1e-1;print;redo}	[reply] [d/l]
Re^4: Uninitialized value in concatenation (.) or string? by jbush82 (Novice) on May 10, 2008 at 21:44 UTC
Re^5: Uninitialized value in concatenation (.) or string? by starbolin (Hermit) on May 11, 2008 at 00:18 UTC
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