There is a recognised way of finding when your variables don't exist, and that is to insert the line

use strict;
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On another note, you might like to try using the super search facility of the monastery, to find if similar questions have been asked before.

rinceWind

One way I have done config files is to setup the config file as a do'able variable in itself that is a reference to a hash.. You can also use Data::Dumper to create the file. config.txt file as such:

$config = \{
            'Variable1' => 'variable value',
            'Variable2' => ['a','b','c'],
           };
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Then you can:

do "config.txt" or die "$! $@";
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This creates a variable $config that is a reference to a hash containing all your configuration variables. If your passing the configuration to subroutines you can just pass $config and your subroutine has access to all the config variables and you saved some overhead.

Granted you have to dereference the hash, but references are a good thing to learn..

if (exists $config->{Variable1}) {}
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Even better is to put your config in a module, with each configuration option being a subroutine declared with an empty prototype (and thus considered by the compiler for inlineing). Example:

package My::Config;

sub VARIABLE1 () { 'variable value' }
sub VARIABLE2 () { [ 'a', 'b', 'c' ] }

1;
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You call it like this:

use My::Config;
my $var1 = My::Config::VARIABLE1;
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Which, if you put this through B::Deparse, will look like:

use My::Config;   # Actually, 
my $var = 'variable value';
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And is thus gives you the advantages of a hard-coded variable without the icky problem of maintainability.

Note, though, that strict won't catch undeclared variables with full package names, so if you do:

my $var1 = My::Config::VAR1;
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strict will happily allow it.

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

: () { :|:& };:

Note: All code is untested, unless otherwise stated

my $var_val;
if(defined($var_val)){
  print "defined";
}
else{
  print "undefined":
}
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my $var_val = 'something';
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NAME
    Env - perl module that imports environment variables as scalars or
+ arrays

SYNOPSIS
        use Env;
        use Env qw(PATH HOME TERM);
        use Env qw($SHELL @LD_LIBRARY_PATH);

DESCRIPTION
    Perl maintains environment variables in a special hash named %ENV.
+ For when this access method is inconvenient, the Perl module "Env" a
+llows environment variables to be treated as scalar or array variable
+s.
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If, for some reason, you can't change how the config file returns things, check if a config var foo is defined with defined($foo) which will return a true or false value.

That just checks to see if the variable has a defined value. The literal answer to your question to check if a variable exists is to check *foo{SCALAR} which will return true (actually, a reference to the variable) if a scalar variable $foo exists. This isn't of much practical use, since code like if (*foo{SCALAR}) { print "foo is $foo"} will always do the print, since the compiler will create the variable before runtime when it sees the $foo. The other problem is that if perl sees any kind of foo variable (hash, array, sub, format, glob) it will create that kind *and* a bonus scalar $foo. So stick with defined($foo).