What causes the warning "Use of uninitialized value" in my program? - perl

Question

This one makes no sense to me. I have these two subroutines.
sub load_config_file {
if (#_ eq '') {
die RED . "No configuration file defined" . RESET . "\n";
} else {
if (! -e "#_") {
die RED . "#_ not found!" . RESET . "\n";
} else {
if (`cat #_` eq '') {
die RED . "$config_file_path is an empty file!" . RESET . "\n\n";
} else {
print "Configuration file:" . GREEN . "#_" . RESET . "\n";
my $xml_obj = XML::Simple->new();
my $config_xml = $xml_obj->XMLin("#_", SuppressEmpty => 1);
%config_file = %$config_xml;
}
}
}
} # End load_config_file
sub load_guest_os_file {
if (#_ eq '') {
die RED . "No guest operating system file defined" . RESET . "\n";
} else {
if (! -e "#_") {
die RED . "#_ not found!" . RESET . "\n";
} else {
if (`cat #_` eq '') {
die RED . "#_ is an empty file!" . RESET . "\n\n";
} else {
print "Guest OS file:" . GREEN . "#_" . RESET . "\n";
my $xml_obj = XML::Simple->new();
my $guest_os_xml = $xml_obj->XMLin("#_", SuppressEmpty => 1);
%guest_os_file = %$guest_os_xml;
}
}
}
} # End load_guest_os_file
Their purpose is to load a specific config file needed for my script. The first one, load_config_file, works perfect. But when I move onto the second one, load_guest_os_file, I get these errors from Perl:
Use of uninitialized value $_[0] in join or string at analyze.pl line 146.
Use of uninitialized value $_[0] in join or string at analyze.pl line 148.
Line 146 in my script is
if (! -e "#_") {
and line 148 is
die RED . "#_ not found!" . RESET . "\n";
What am I missing? When I call the subroutine thus:
load_config_file($config_file_path)
load_guest_os_file($guest_os_file_path)
… the values assigned to those two variables are
my $config_file_path = './config.xml'
and
my $guest_os_file_path = './guest_os.xml'
Edit: I should also add the values for the two variables coming from the command line arguments processed by Getopt::Long. If no value is assigned, the variable is just "declared", I think that's the term. I do not assign a value to it, it's just my $config_file_path; and my $guest_os_file_path;.
Update
Here is the code from the beginning of the script.
#!/usr/bin/perl
use strict;
use warnings;
# Modules to load
use Getopt::Long;
use Term::ANSIColor qw(:constants);
use XML::Simple;
use Net::Ping;
use Net::OpenSSH;
use Data::Dumper;
# Script version
my $version = 'v0.6';
my (%config_file, %guest_os_file, %machines_xml, $ssh_obj);
my #selected_mode;
# Configuration file
my $config_file_path;
# Guest OS file
my $guest_os_file_path;
# Exclusion file
my $exclude_file_path;
# Disables snapshot capture
my $no_snapshots = 0;
my $logfile_path;
my $verbose = 0;
# Program modes
my %program_modes = (
analyze => \&analyze,
backup => \&backup,
restore => \&restore,
help => \&help,
);
GetOptions(
'c=s' => \$config_file_path,
'e=s' => \$exclude_file_path,
'g=s' => \$guest_os_file_path,
'l=s' => \$logfile_path,
'v' => \$verbose,
'x' => \$no_snapshots,
'a' => sub { push #selected_mode, "analyze" },
'b' => sub { push #selected_mode, "backup" },
'h' => sub { push #selected_mode, "help" },
'r' => sub { push #selected_mode, "restore" },
's' => sub { push #selected_mode, "setup" },
);
# Show the help menu if no program mode has been selected
if (#selected_mode == 0) {
help();
# Throw an error and show the help menu if too many modes are selected
} elsif (#selected_mode > 1) {
print RED . "Too many program modes specified" . RESET . "\n";
print "See help menu [-h] for further information\n";
# Run the selected program mode
} elsif (#selected_mode == 1) {
if ($selected_mode[0] eq 'help') {
help();
} else {
# Die unless user is root
die RED . "You must be have superuser permissions to run this script" . RESET . "\n" unless ($> == 0);
system "clear";
print "Solignis's VMware $selected_mode[0] script $version for ESX\\ESX(i) 4.0+\n";
load_config_file($config_file_path);
if ($selected_mode[0] eq 'analyze') {
load_guest_os_file($guest_os_file_path);
} else {
######
}
}
}

Answer 1

This will always be false:
if (#_ eq '') {
When empty, the array gives 0 in scalar context, not ''.
Just:
if ( ! #_ ) {
is sufficient to test if there was nothing passed.
But I think you actually mean to insure a defined value was passed:
if ( ! defined $_[0] ) {
To know why it $_[0] is undefined, we'd have to see the code from the declaration to where it is passed to the sub.

Answer 2

Some genereal pointers on your code:
Consider using elsif instead of the ever nesting else blocks.
If you have a bunch of error conditions you're filtering out, consider using statement modifier if/unless logic.
Consider using -z or -s to get your file size ( see http://perldoc.perl.org/functions/-X.html ).
Unpack #_ at the top of your subroutines.
Minimize use of global variables. Explicitly pass all data in and out of your subs.
Here's a cleaned up version of your first sub:
sub load_config_file {
my $config_file = shift;
die RED . "No configuration file defined" . RESET . "\n"
unless defined $config_file;
die RED . "$config_file not found!" . RESET . "\n"
unless -e $config_file;
die RED . "$config_file_path is an empty file!" . RESET . "\n\n"
if -z $config_file;
print "Configuration file:" . GREEN . "#_" . RESET . "\n";
my $xml_obj = XML::Simple->new();
my $config_xml = $xml_obj->XMLin("#_", SuppressEmpty => 1);
return $config_xml;
} # End load_config_file
BTW, I am not sure what you have going on with the REDs and RESETs in your die messages, but I have a feeling that it could be better achieved with an exception handler.

Answer 3

If you use the subs with only one value, you might as well copy that over to a variable, instead of using #_, like so:
sub load_guest_os_file {
my $path = shift;
The tests you are performing can be done better, and they do not need to be inside each other, since the only result is die:
$path || die RED . "No guest operating system file defined" . RESET . "\n";
-e $path || die RED . "$path not found!" . RESET . "\n";
-s $path || die RED . "$path is an empty file!" . RESET . "\n\n";
The -e check is not functionally necessary, as -s will fail also if the file is missing. It will give a better error, though.
Also, if you are using arguments to your function, it might be more consistent to not manipulate global variables with the sub, and instead give a return value, such as:
...
return %$config_xml;
}
%config_file = load_config_file($config_file_path);

Answer 4

In order to get the warnings mentioned above, the first parameter to subroutine load_guest_os_file has to be undefined (which is the default value after declaration).
From the source code you have shown, the only possibility I can see for this scenario to happen is that no valid option -g<path> was given, and so variable $guest_os_file_path is never assigned a value. Then subroutine load_guest_os_file would be called with an undefined value as its parameter like this
load_guest_os_file(undef)
and Perl would give these warnings.