How to properly declare global variables in Perl? - perl

Question

I am trying to understand variable scope and properly declaring variables in Perl, and I am having a hard time.
The code below basically reads in an excel file, parses it, and spits it out to a new excel file.
However, I am trying to read one of the headers, and if the header matches my string, I want to record that column number, and use it later in the code.
I am getting a "Use of uninitialized value $site_name_col in print at ./parser.pl line 38."
Line 38 is "print $site_name_col;"
I realize this print statement is outside the {} where the variable was initially initialized, but it was declared as a global variable at the beginning of the code, so what gives?
#!/usr/bin/perl -w
use strict;
use warnings;
use vars qw($site_name_col);
use Spreadsheet::WriteExcel;
use Spreadsheet::ParseExcel;
my ($fname1) = #ARGV;
my $parser = Spreadsheet::ParseExcel->new();
my $workbook = $parser->parse($fname1);
my $new_workbook = Spreadsheet::WriteExcel->new('formated_list.xls', $fname1);
if (!defined $workbook) {
die $parser->error(), ".\n";
}
for my $worksheet ( $workbook->worksheets() ) {
my ($wsheet_name) = $worksheet->get_name();
my $new_worksheet = $new_workbook->add_worksheet($wsheet_name);
my ($row_min, $row_max) = $worksheet->row_range();
my ($col_min, $col_max) = $worksheet->col_range();
for my $row ($row_min .. $row_max) {
for my $col ($col_min .. $col_max) {
my $cell = $worksheet->get_cell($row, $col);
next unless $cell;
print "Row, Col = ($row, $col)\n";
if ( $cell->value() =~ /Site Name/ ) {
$site_name_col = $col;
}
print $site_name_col;
$new_worksheet->write($row, $col, $cell->value());
}
}
}
$new_workbook->close();

Answer 1

use vars qw() Is not recommended any more. To declare a global variable use our $my_var
Your problem may be comes from the condition $cell->value() =~ /Site Name/ . It is probably never met so your variable never gets a value.

Answer 2

i recognize this post is a little old, but...for those still coming to this page years later (like myself):
i imagine these excel worksheets you were reading in may not have been created by you. so, you may encounter casing issues, and regexes are case sensitive, of course. either uppercase or lowercase the data during the check: if (lc($cell->value()) =~ /site name/) ...
use our! there are lots of reasons for one to have a global. site_name would seem to be something all files might need...
Jarett
edit:
this will work much better:
if ($cell->value()) =~ /site name/i) { print $col; }
no need to print outside the if statement at all...saves printing nothing many...many times....

Answer 3

Just to clarify what others have already said, a variable declared at the top of a file with my is accessible and usable by your entire file. There is no reason for a global variable in this case.
When would you want a global?
You want a variable to be accessible by another piece of code outside of your file. For example, a module might provide a global variable that is accessible by files that call the module.
You have multiple packages within one file. In which case, you would need a global variable for something accessed by both packages. It would be rather unusual to do this, however.
It is pretty clear that you aren't doing either of those things, so you should just stick with my. If you do want to declare a global, the correct way to do so is with our. There are some important subtleties to that command, explained in the linked documentation.

Answer 4

You don't need to declare global variable in this case, local variable is enough. See example below.
if ( $cell->value() =~ /Site Name/ ) {
my $site_name_col = $col;
print $site_name_col;
}
OR
my $site_name_col = ''; # default value
if ( $cell->value() =~ /Site Name/ ) {
$site_name_col = $col;
}
print $site_name_col;