Strange Global Array issue

[Anonymous Monk]

Hi all!

I've run into a strange issue with a global array that is being populated by values that (on the face of it) I can't figure out why.

I'm using strict/warnings, and have used Data::Dumper to find the point where the value of my global array is changing. Basically, I have a global array of hashes, with each key being the "type" of a regular expression (I have multiple regular expressions to run on a certain file type, with each regular expression looking for/at a specific part of the file) . The global array is declared at the top of the script:

my @regexes = ();

In a foreach loop within a subroutine, I make a call to another sub:

foreach (@regexes){
($fileBodyMatch, $decode ) = checkFileBody ($file, $_->{bodyregex});
}

The array looks fine before this subroutine call. The value of "$decode" is what I'd expect it to be. In the subroutine checkFileBody, I do the following ($filename is the $file value being passed in) :

open ( DKT, "gunzip -c $filename | ") or die "Can't open pipe to $file
+name\n";

At this point, everything still looks good in Dumper. I then do this:

while (<DKT>){
 my $line =$_;
#process data in here
}

Even before I have the "my $line" declaration I have a Data Dumper call to print out the contents of @regexes and the @regexes array contains the last line of the file read and nothing else.

At the conclusion of the sub, the net result is that the @regexes array contains the last line of the file as the first element of the array, followed by the previous (valid) contents.

Thank you in advance!

[hdb]

Have you tried to remove the reliance on $_ in your sub?

while (my $line = <DKT>){
# my $line =$_;
# process data in here
}

[Anonymous Monk]

First of all, that did the trick. Thanks!

Second (and more importantly for my understanding of Perl), would you mind explaining why that would be the fix?

[hdb]

There is only one $_ in your program and you did use it for two different purposes. One has to be careful sometimes with Perl's build-in variables.

From "Modern Perl", page 7: http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf

As English gets confusing when you have too many pronouns and antecedents, you must take care mixing uses of $_ implicitly or explicitly. Uncautious simultaneous use of $_ may lead to one piece of code silently overwriting the value written by another. If you write a function which uses $_, you may clobber a caller function's use of $_.

UPDATE: In order to make your script more robust overall, you might also want to remove $_ from your outer loop.

foreach my $regex (@regexes){
    ($fileBodyMatch, $decode ) = checkFileBody ($file, $regex->{bodyre
+gex});
}