Just to add to kcott’s excellent answer:

If you have a string like "$VAR1 = '-39.9999400000';\n" and want to get the number inside, you can either eval the string and use $VAR1, or else extract the number with a regular expression:

#! perl
use strict;
use warnings;
use Data::Dumper;

      my @lines  = <DATA>;
chomp(my $line   = $lines[0]);
chomp(my $string = Dumper("$line"));

print "Dumper returns the string \"$string\"\n";

# Method 1: eval the string

my    $VAR1;
eval  $string;      # Sets $VAR1
my    $m = $VAR1 + 8;
print "Method 1: $m\n";

# Method 2: extract the number

if ($string =~ /'([-0-9.]+)'/)
{
    my    $value = $1;
    my    $n     = $value + 8;
    print "Method 2: $n\n";
}

__DATA__
-39.9999400000
[download]

Output:

23:27 >perl 730_SoPW.pl
Dumper returns the string "$VAR1 = '-39.9999400000';"
Method 1: -31.99994
Method 2: -31.99994

23:27 >
[download]

See chomp, eval, and perlretut.

Hope that helps,