B::Deparse reveals all:

$ perl -MO=Deparse
package foo;

sub ARGV { print "in foo::ARGV\n" }

package main;

foo->ARGV;

package foo;
sub main::ARGV {
    print "in foo::ARGV\n";
}
package main;
'foo'->ARGV;
- syntax OK
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I haven't yet found the part of the parser which forces sub ARGV into main::.

Interestingly enough, if you add use strict (at least on 5.8.9 and 5.10.1) to package foo, B::Deparse does not reveal all, like so:


package foo;
sub BEGIN {
    require strict;
    do {
        'strict'->import
    };
}
sub ARGV {
    use strict 'refs';
    print "in foo::ARGV\n";
}
package main;
use strict 'refs';
'foo'->ARGV;
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(in fact just making sub ARGV not the first line of code after package foo is enough to confuse B::Depase in this.

The special variables are "super global"*, accessible from any namespace without qualification. This is done by making the name of the variable "super global". That means that if $_ is super global, so is array @_, hash %_, sub &_, etc.

"ARGV" is one of those names. No matter what namespace is current, sub ARGV { } will define &main::ARGV, and ARGV() will call &main::ARGV.

You can get around that by specifying which package's ARGV you want.

{
   package Foo;
   sub ARGV      { print "1\n" }
   sub Foo::ARGV { print "2\n" }
}

{
   package Bar;
   ARGV();        # 1
   Foo::ARGV();   # 2
   Foo->ARGV();   # 2
}
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Replace "ARGV" with "_" and you'll get the same results.

* — Not a technical term :)

sub foo::ARGV { print "in foo::ARGV\n" }
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ARGV

The special filehandle that iterates over command-line filenames in @ARGV . Usually written as the null filehandle in the angle operator <> . Note that currently ARGV only has its magical effect within the <> operator; elsewhere it is just a plain filehandle corresponding to the last file opened by <> . In particular, passing \*ARGV as a parameter to a function that expects a filehandle may not cause your function to automatically read the contents of all the files in @ARGV .

ARGV: It's more than just an array!

Update: And if you really want to do what you appear to want to do, running this script:

#!/usr/bin/perl
use strict;
use warnings;

package foo;

sub fake_ARGV { print "in foo::ARGV\n" }
no warnings "once";
*foo::ARGV = *foo::fake_ARGV;

package main;

foo->ARGV;
print $ARGV[0];
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~/sandbox$ perl test.pl 'Still here'
in foo::ARGV
Still here
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That is not required, all is required is this:

package foo;
use strict;

sub foo::ARGV { print "in foo::ARGV\n" }

package main;
foo->ARGV;
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Also note that rational is not a noun and that they're pronounced differently: "rational" is something like "RASH-ən-əl" and "rationale" is something like "rash-ən-AL" (rhyming neither with "all" nor "ale", but with the shortened form of "Albert").