$ cat test.xml
<?xml version="1.0"?>
<filelist>
<file name="file1">
  <field name="field1" start="50"  length="20"/>
  <field name="field2" start="80"  length="20"/>
  <field name="field3" start="100"  length="20"/>
</file>
<file name="file2">
  <field name="field1" start="52"  length="22"/>
  <field name="field2" start="82"  length="22"/>
  <field name="field3" start="120"  length="22"/>
</file>
<file name="file3">
  <field name="field1" start="53"  length="23"/>
  <field name="field2" start="83"  length="23"/>
  <field name="field3" start="130"  length="23"/>
</file>
</filelist>


$ perl -MXML::Simple -MData::Dumper -e '$x=XMLin("test.xml"); print Dumper($x)'

$VAR1 = {
          'file' => {
                    'file2' => {
                               'field' => {
                                          'field1' => {
                                                      'length' => '22',
                                                      'start' => '52'
                                                    },
                                          'field2' => {
                                                      'length' => '22',
                                                      'start' => '82'
                                                    },
                                          'field3' => {
                                                      'length' => '22',
                                                      'start' => '120'
                                                    }
                                        }
                             },
                    'file1' => {
                               'field' => {
                                          'field1' => {
                                                      'length' => '20',
                                                      'start' => '50'
                                                    },
                                          'field2' => {
                                                      'length' => '20',
                                                      'start' => '80'
                                                    },
                                          'field3' => {
                                                      'length' => '20',
                                                      'start' => '100'
                                                    }
                                        }
                             },
                    'file3' => {
                               'field' => {
                                          'field1' => {
                                                      'length' => '23',
                                                      'start' => '53'
                                                    },
                                          'field2' => {
                                                      'length' => '23',
                                                      'start' => '83'
                                                    },
                                          'field3' => {
                                                      'length' => '23',
                                                      'start' => '130'
                                                    }
                                        }
                             }
                  }
        };