Help with recurring "uninitialized variable" problem.

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

Greetings most wise and helpful monks!

For whatever reason, this problem keeps cropping up, so I'm hoping someone can shed some light on the problem so I can eliminate it once and for all.

This code works:

while (<>)
{
  if (!/^#+/)
  {
    ($source, $destination, $bytes) = split;
    $net_activity{$source}{$destination} += $bytes;
  }# ignore comments
}# read in each line of the net log
[download]

This code does not:

my($one_line) = '';
while ($one_line = <>)
{
  if ($one_line =~ !/^#+/)
  {
    ($source, $destination, $bytes) = split(/ /, $one_line);
    $net_activity{$source}{$destination} += $bytes;
  }# ignore comments

}# read in each line of the net log
[download]

I get lots of these:

Use of uninitialized value in pattern match (m//) at ./net_traffic2 li
+ne 14, <> line 5.
[download]

The program still WORKS (i.e. does what it's supposed to do), but it throws up all those warnings first.

I know I'm doing something Very Dumb(TM) here, but if someone could point it out I'd be extremely grateful. I want to understand this whole "unitialized variable" thing because it keeps coming up even when I think I've initialized the variable. Apparently Perl and I have different ideas of what that means, so I want to get in line.

Many thanks!

C_T

Charles Thomas
Madison, WI

Comment on Help with recurring "uninitialized variable" problem. Select or Download Code

Replies are listed 'Best First'.
Re: Help with recurring "uninitialized variable" problem. by Not_a_Number (Prior) on Apr 09, 2004 at 17:15 UTC
Change `if ($one_line =~ !/^#+/)` to `if ($one_line !~ /^#+/)` or `unless ($one_line =~ /^#+/)` or if you really want `if (!($one_line =~ /^#+/))` (and by the way you can drop the '+' in the regex) dave	[reply] [d/l] [select]
Re: Re: Help with recurring "uninitialized variable" problem. by C_T (Scribe) on Apr 09, 2004 at 17:25 UTC
`if (!($one_line =~ /^#+/))` [download] That did the trick! I THINK I understand why... `!~` is a new one on me, BTW. Very cool. Many thanks! CT Charles Thomas Madison, WI	[reply] [d/l] [select]
Re: Re: Re: Help with recurring "uninitialized variable" problem. by Fletch (Bishop) on Apr 09, 2004 at 17:54 UTC
`B::Deparse` can shed some light . . . `$ perl -MO=Deparse,-p -e '$one_line =~ !/^#+/' ($one_line =~ (not /^#+/));` [download] So what you were really doing was first matching `/^#+/` against `$_`, taking the logical not of what that returned and then attempting to use the string version of that as a regexp to match against `$one_line`. Update: And to further explain, that meant you were always splitting and hence would sometimes get lines without all the fields you expected and those would be undefined.	[reply] [d/l] [select]
Re: Re: Re: Re: Help with recurring "uninitialized variable" problem. by C_T (Scribe) on Apr 09, 2004 at 20:35 UTC
Re: Re: Re: Re: Re: Help with recurring "uninitialized variable" problem. by Fletch (Bishop) on Apr 09, 2004 at 22:24 UTC
Re: Help with recurring "uninitialized variable" problem. by Ovid (Cardinal) on Apr 09, 2004 at 16:52 UTC
Try this: `while (defined (my $one_line = <>)) { if ($one_line =~ !/^#+/) { ($source, $destination, $bytes) = split(/ /, $one_line); $net_activity{$source}{$destination} += $bytes; }# ignore comments }# read in each line of the net log` [download] Cheers, Ovid New address of my CGI Course.	[reply] [d/l]
Re: Re: Help with recurring "uninitialized variable" problem. by C_T (Scribe) on Apr 09, 2004 at 16:58 UTC
Ovid wrote: Try this: `while (defined (my $one_line = <>))` [download] This gives the same warnings, I'm afraid. C_T Charles Thomas Madison, WI	[reply] [d/l]
Re: Re: Re: Help with recurring "uninitialized variable" problem. by Ovid (Cardinal) on Apr 09, 2004 at 17:12 UTC
How are you getting your values in `@ARGV`? I think one of more of them is `undef`. As a quick test, try adding the following line before the while loop. If it suppresses the warnings, you have `undef` values there. `@ARGV = grep defined() => @ARGV;` Cheers, Ovid New address of my CGI Course.	[reply] [d/l]


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