$a = $a * 2
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Which you means you have to build that string and pass it to the parser (eval EXPR). That can be done using the string literal

"\$$v = \$$v * 2"
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So you want

eval "\$$v = \$$v * 2; 1" or die $@;
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Thanks!

I see that I need to look at the string being passed to eval().

Thanks, again for slapping me back to reality. I guess it's getting late...

The values you pass into a subroutine are aliased, in other words, the elements of @_ are actually the variables you passed in and whatever you do to the elements of @_ happens to the original variables.

Consider:

use Modern::Perl;
use PadWalker qw/peek_my peek_our/;

my ($first,$second, $third) = qw /1 2 3/;

double_me($first,$second, $third);

say "$first $second $third";

sub double_me {
    say get_name(1, $_) for @_;
    $_*=2 for @_;
}

sub get_name_my {
    my $pad = peek_my($_[0] + 1);
    for (keys %$pad) {
        return $_ if $$pad{$_} == \$_[1]
    }
}
sub get_name_our {
    my $pad = peek_our($_[0] + 1);
    for (keys %$pad) {
        return $_ if $$pad{$_} == \$_[1]
    }
}
sub get_name_stash {
    my $caller = caller($_[0]) . '::';
    my $stash = do {
        no strict 'refs';
        \%$caller
    };
    my %lookup;
    for my $name (keys %$stash) {
        if (ref \$$stash{$name} eq 'GLOB') {
            for (['$' => 'SCALAR'],
                 ['@' => 'ARRAY'],
                 ['%' => 'HASH'],
                 ['&' => 'CODE']) {
                if (my $ref = *{$$stash{$name}}{$$_[1]}) {
                    $lookup{$ref} ||= $$_[0] . $caller . $name
                }
            }
        }
    }
    $lookup{\$_[1]}
}
sub get_name {
    unshift @_, @_ == 2 ? 1 + shift : 1;
    &get_name_my  or
    &get_name_our or
    &get_name_stash
}
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$first
$second
$third
2 4 6
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1. Because of the aliasing it is considered a "Perl Best Practice" to immediately assign @_ to lexical variables in the subroutine, so as not to have any inadvertent effect "at a distance" on the original variables. Of course this is exactly what you want to happen here, so go ahead!
2. I have found the solution to get your variable names on StackOverFlow

#!/bin/env perl

use strict;
use warnings;

my ($a, $b, $c);
$a = $b = $c = 0;
foreach my $v (qw/a b c/) {
    func($v);
}

sub func {
    my $v = shift;
    print "v = $v\n";
    eval '$'.$v.' = $'.$v.' * 2';
}

print "$a $b $c\n";
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our ($a, $b, $c) = (0, 0, 0);
foreach my $v (qw/a b c/) {
    func($v);
}
sub func {
    my $v = shift;
    print "v = $v\n";
    no strict 'refs';
    $$v *= 2;
}
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Slightly off topic but you can also use an anonymous function rather than the eval. This is what I quickly came up with:

#!/bin/env perl

use strict;
use warnings;
use 5.012;

my ($a, $b, $c);
$a = $b = $c = 0;
foreach my $v (qw/a b c/) {
    func($v);
}

sub func {
    my $in = shift;
    say "passed in: $in";
    print "returned: ";
    return sub {
        my $in = shift;
        say $in x 2;
        }->($in);
}
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Actually, disregard that as it still won't work with $a, $b, $c rather than a, b, c... Humble apologies, I misread your question!