Getting a substring of an attribute in XPATH

Given

<foo>
  <bar baz="Hello, World!">
</foo>

开发者_如何学GoHow do I all but the last 4 characters of @baz? One of my attempts was:

/foo/bar/@baz[substring( ., 0, -4 )]

Use:

substring(/foo/bar/@baz, string-length(/foo/bar/@baz)-3) 

Do note the 3 in the expression.

The following is wrong:

substring(/foo/bar/@baz, string-length(/foo/bar/@baz)-4) 

because this returns the last 5 characters of the string value of the baz attribute.

try this: substring-before(/foo/bar/@baz,"rld!")

That's actually not so bad, but IIRC substring doesn't like negative indices. I tried

substring(/foo/bar/@baz, string-length(/foo/bar/@baz)-4)

Which gave me the expected result.