in reply to globally seen vairable

Is there a way to introduce a variable which is defined in the main program and is seen from external modules.

Sure. See our.

What is a drawback of such a variable

There is extensive literature out there, for example search for why are global variables bad. In short: global state makes programs harder to understand, to debug, can cause problems with recursion and concurrency, and is often a sign of bad encapsulation.

Perl 6 - links to (nearly) everything that is Perl 6.

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Re^2: globally seen variable
by vit (Friar) on Sep 28, 2010 at 18:15 UTC
    In this example from perldoc will not $bar declared "our" in Foo conflict in package Bar with "use strict" ? 
    package Foo;
our $bar; # declares $Foo::bar for rest of lexical scope
$bar = 20;
..........................
#
package Bar;
use strict;
print $bar; # prints 20, as it refers to $Foo::bar

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[d/l]
      Why should it?

      our $bar creates an entry in the current package, and a lexical alias to it. The lexical alias persists to the next package too, because packages and lexical scopes are completely orthogonal.

      Perl 6 - links to (nearly) everything that is Perl 6.
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[d/l]
        I declared 
        our $ERROR_FILE            = $cgi_dir."files/logs/errors.txt";

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        in main program and tried to use it in package: 
        use strict;

package RecordError;

sub RecordError
{
my $error = shift;

## $ERROR_FILE is global var ##

open OF, ">>$ERROR_FILE" or die "cannot open ERROR_FILE $ERROR_FILE\n"
+;
print OF "$error\n";
close OF;
}
1;

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        and it returns 
        Global symbol "$ERROR_FILE" requires explicit package name at E:/.....
+./lib/RecordError.pm line 12.

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        What do I do wrong?
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[d/l]
[select]

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