use warnings;

With warnings turned on, perl will tell you there are syntax errors.

Here is a stripped version of your code:

use strict;
use warnings;

my $file = (<DATA>);


Data___
<?xml version="1.0"?>

<opt>
  <node>
    <val>1</val>
  </node>
  <node>
    <val>2</val>
  </node>
  <node>
    <val>3</val>
  </node>
</opt>
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Here is the warings:

Number found where operator expected at c.pl line 12, near "<val>1"
        (Missing operator before 1?)
Bareword found where operator expected at c.pl line 13, near "</node"
  (Might be a runaway multi-line // string starting on line 12)
        (Missing operator before node?)
Bareword found where operator expected at c.pl line 16, near "</node"
  (Might be a runaway multi-line // string starting on line 15)
        (Missing operator before node?)
Bareword found where operator expected at c.pl line 19, near "</node"
  (Might be a runaway multi-line // string starting on line 18)
        (Missing operator before node?)
syntax error at c.pl line 8, near "?xml version="1.0"?>"
Execution of c.pl aborted due to compilation errors.
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use __DATA__, then the warnings go away.