my $foo;
my $bar = '043';

my $s1 = '$foo = $bar';
print "s1: ", $s1, "\n";
print "eval=", eval($s1)//$@, ", \$foo=$foo\n";

my $s2 = "\$foo = $bar"; # same as '$foo = '.$bar
print "s2: ", $s2, "\n";
print "eval=", eval($s2)//$@, ", \$foo=$foo\n";

__END__

s1: $foo = $bar
eval=043, $foo=043
s2: $foo = 043
eval=35, $foo=35

##</code><code>##

use Data::Dump;

my $val = "034";
$val = oct $val if $val=~/^0/;
dd $val;   # 28

# or, for a list of values:
my @vals = qw/ 10 20 0b1101 0xF 023 /;
/^0/ and $_=oct for @vals;
dd @vals;  # (10, 20, 13, 15, 19)