The issue in your case is related to the encoding mismatch between the XML file and the tool (xmlstarlet) processing it. Here's what's happening:

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Root Cause

1. XML Declaration: Your test.xml file declares its encoding as UTF-16:

   xml
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   <?xml version="1.0" encoding="UTF-16"?>

   However, the actual content of the file is likely not encoded in UTF-16. The file appears to be in a different encoding (possibly UTF-8 or ASCII), but the declaration explicitly states UTF-16.

2. xmlstarlet Behavior:

   • xmlstarlet reads the XML declaration and expects the file to be in UTF-16.
   • If the file is not actually UTF-16, xmlstarlet will fail to parse it, resulting in the error:

     text
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     parsing XML declaration: '?>' expected

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How to Fix It

Option 1: Change the XML Declaration

If your file is not UTF-16 encoded (e.g., it's UTF-8 or ASCII), update the XML declaration to match the actual encoding:

xml
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<?xml version="1.0" encoding="UTF-8"?>

Then save the file as UTF-8.

Option 2: Convert the File to UTF-16

If you want to keep the declaration as UTF-16, ensure the file is actually saved in UTF-16 encoding. You can do this using tools like:

• iconv (Linux/macOS):

  bash
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  iconv -f UTF-8 -t UTF-16 test.xml > test_utf16.xml

• Text editors (e.g., Notepad++, VS Code) that allow you to save files in specific encodings.

Option 3: Force xmlstarlet to Ignore Encoding

If you are sure the file is UTF-8 but misdeclared, you can preprocess it to remove the encoding attribute or use a tool like recode to fix it.

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Testing the Fix

After fixing the encoding, run your command again:

bash
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cat test.xml | xmlstarlet sel -t -v '//node/@bounds'

If the file is correctly encoded, this should work without errors.

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