require 'rexml/document'
  
  doc = REXML::Document.new(File.open("test.xml"))
  root = doc.root
    rtnValue = root.get_elements("COM1")
  #rtnValue = root.elements["COM1"].text
  rtnValue.each{|re|
    puts re.text
  }
  #puts  rtnValue

XML文件：

<?xml version="1.0" encoding="UTF-8"?>
<Root>
  <COM1>AAAAAAAAAAA</COM1>
  <COM1>AAAAAAAAbbb</COM1>
  <COM2>BBBBBBBBBBB</COM2>
  <COM3>CCCCCCCCCCC</COM3>
  ...
  ...
</Root>