Using # and $ with the same variable name in Perl - perl

Question

I am declaring the same variable name with # and $:
#ask=(1..9);
$ask="insanity";
print ("Array #ask\n");
print ("Scalar $ask\n");
Without using use strict I am getting output correctly but when I am using use strict it gives me a compilation error.
Do these two variables refer to two different memory locations or is it the same variable?

Answer 1

You've got two variables:
#ask
$ask
You could have %ask (a hash) too if you wanted. Then you'd write:
print $ask, $ask[0], $ask{0};
to reference the scalar, the array and the hash.
Generally, you should avoid this treatment, but the variables are all quite distinct and Perl won't be confused.
The only reason use strict; is complaining is because you don't prefix your variables with my:
#!/usr/bin/env perl
use strict;
use warnings;
my #ask = (1..9);
my $ask = "insanity";
my %ask = ( 0 => 'infinity', infinity => 0 );
print "Array #ask\n";
print "Scalar $ask\n";
print "Hash $ask{0}\n";

Answer 2

with use strict; you need to declare your variables first before using it.
For example:
use strict;
my #ask=(1..9);
my $ask="insanity";
print ("Array #ask\n");
print ("Scalar $ask\n");

Answer 3

#ask and $ask are different variables — as is %ask — and it is not an error to do this. It is however poor style.
Because the sigil changes when you use them, such as when you use $ask[1] to get the second element of #ask, the code becomes harder to read and use strict will also not be able to tell if you've gotten confused. Thus it's a good idea to use names that differ in more than the sigil unless you know what you're doing. So you could use e.g. #asks and $ask.

Answer 4

The error you are getting with strict is not due to variable names. It is because you are not declaring the variables (using one of my, our, local, or state. Nor are you using the vars pragma.
Short answer: Stick a my in front of each variable, and you'll be strict-compliant.
For package variables, you can examine entries in the symbol table. $ask and #ask are separate entities:
#!/usr/bin/env perl
use Devel::Symdump;
use YAML;
#ask=(1..9);
$ask="insanity";
my $st = Devel::Symdump->new('main');
print Dump [ $st->$_ ] for qw(
scalars
arrays
);
Among other things, this code will output:
--
…
- main::ask
…
---
…
- main::ask
…
Being able to use the same name can help when, say, you have an array of fish and you are doing something with each fish in the array:
for my $fish (#fish) {
go($fish);
}
Normally, it is more expressive to use the plural form for arrays and hashes, the singular form for elements of an array, and something based on the singular form for keys in a hash:
#!/usr/bin/env perl
use strict;
use warnings;
my #ships = ('Titanic', 'Costa Concordia');
my %ships = (
'Titanic' => {
maiden_voyage => '10 April 1912',
capacity => 3_327,
},
'Costa Concordia' => {
maiden_voyage => '14 July 2006',
capacity => 4_880,
},
);
for my $ship (#ships) {
print "$ship\n";
}
while (my ($ship_name, $ship_details) = each %ships) {
print "$ship_name capacity: $ship_details->{capacity}\n";
}