Outside of a *subroutine*, the default variable for list operations is @ARGV. Inside a subroutine, it's @_. Since none of your code occurs inside a subroutine, it's all attempting to operate on @ARGV.

Note, though, that while @_ is a respectable global, the @_ your subroutine sees is local to the subroutine. So unless you *explicitly* pass arguments to the subroutine, what you set @_ outside the subroutine won't make any valuables (update or, indeed, *values* =) available to the subroutine. i.e. :

sub jah {
        while (my $d = shift) {
             print "$d\n";
        }
}
@_ = qw(foo bar bat);
jah(); # produces no output
jah(qw(foo bar bat)); # produces output
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HTH

perl -e 'print "How sweet does a rose smell? "; chomp ($n = <STDIN>); 
+$rose = "smells sweet to degree $n"; *other_name = *rose; print "$oth
+er_name\n"'
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but &jah; would produce output.

arturo is mostly correct about what shift defaults to, but note that there are exceptions (that you are unlikely to encounter anytime soon) where shift will take @ARGV by default within a subroutine. See the docs for more details.

If shift "is not really a function", what is it? And I thought only *subroutines* were called with &. shift certainly isn't a subroutine.

The words subroutine and function are often used interchangably in perl. (Even perlsub does it!) What I meant by calling shift "not really a function" was that it is very unlike the functions you define in your code, which have a symbol table entry and thus are associated with a package, can have coderefs be taken of them, and be aliased to other names at the symbol table entry, or imported into other packages, in addition to being callable by the & syntax.

my $n = shift @_;

Really, I do not recommend explicitly defining the @_ var, but I hope it is just for example purposes.

So in that case....

#! /usr/bin/perl -w
use strict;

@_ = qw( Lucy, I'm home! );

sub main {
while(my $d = shift) {
    print "$d\n";
}
}

&main;
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You can use this if it really upsets you.

However, assuming your code is not just an example, why in the world are you using the @_ array??? And if your not explicitly defining something to @_, there should not be a variable to read in the main. The package main should always be called first on program execution, and should have @ARGV, and the variables you assigned (globally...). (Side note, yes, I know other built-ins are there, but these are really the vars he needs to deal with.)

Dont just think of @_, $_, etc, as "default variables", but more as pronouns. "These are as bad as it." Is not a proper sentence, and a worse program. "These are apples, and it is an orange. These cannot compare to it." Now the sentence makes no sense for a reason other than bad grammar.

So from what I can tell, you're doing something you shouldn't, and perl is making you type three more charachters... Whatta language.

What would happen to this:

#!/usr/bin/perl -w
use strict;

@_ = qw( hello world )
@other = qw( hasta la vista baby )

sub main {
while(my $d = shift) {
    print "$d\n"; # Are we coming or going?
    }
}

&main;
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The code actually reads the @_ array, which it should, but more importantly, you can't tell if you're coming or going just from reading it.

Bad monky...

~Hammy

-n0mad-