xpath expression for regex-like matching?

Question

I want to search div id in an html doc with certain pattern. I want to match this pattern in regex:

foo_([[:digit:]]{1.8})

using xpath. W

Answer 1

How about this (updated):

XPath 1.0:

"//div[substring-before(@id, '_') = 'foo' 
       and substring-after(@id, '_') >= 0 
       and substring-after(@id, '_') <= 99999999]"

Edit #2: The OP made a change to the question. The following, even more reduced XPath 1.0 expression works for me:

"//div[substring(@id, 1, 13) = 'post_message_' 
       and substring(@id, 14) >= 0 
       and substring(@id, 14) <= 99999999]"

XPath 2.0 has a convenient matches() function:

"//div[matches(@id, '^foo_\d{1,8}$')]"

Apart from the better portability, I would expect the numerical expression (XPath 1.0 style) to perform better than the regex test, though this would only become noticeable when processing large data sets.

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Original version of the answer:

"//div[substring-before(@id, '_') = 'foo' 
       and number(substring-after(@id, '_')) = substring-after(@id, '_') 
       and number(substring-after(@id, '_')) >= 0 
       and number(substring-after(@id, '_')) <= 99999999]"

The use of the number() function is unnecessary, because the mathematical comparison operators coerce their arguments to numbers implicitly, any non-numbers will become NaN and the greater than/less than tests will fail.

I also removed the encoding of the angle brackets, since this is an XML requirement, not an XPath requirement.