Does xpath explicitly allow undefined variables?

Question

I was trying to pull some data out of an XML file using xmlstarlet, but

xmlstarlet sel -t  -v '//div[contains(@class,'addresses')]/a'

was getting me a lot more than I expected.

I finally worked out - with the help of replacing -v with -c to debug the xpath - that it was because the single quotes around 'addresses' were vanishing because the whole argument is single-quoted: replacing that with "addresses" worked as expected.

What I'm really confused about is quite what contains(@class,addresses) does - because xmlstarlet didn't flag it as an error or warn about it, even though I presume it's treated as an undefined variable.

I checked the source in https://github.com/fishjam/xmlstarlet/blob/master/src/xml_select.c but I can't spot a 'warnings' flag - should there be something like that, or are xpaths defined to allow this?

Martin Honnen · Accepted Answer · 2023-05-07 14:58:57Z

2

In contains(@class,addresses), addresses selects (possible) child elements named addresses of the context node (i.e. in //div[contains(@class,addresses)] the div element the predicate [contains(@class,addresses)] belongs to); a variable (reference) would be written as $addresses.

edited May 7, 2023 at 14:58

answered May 7, 2023 at 14:48

Martin Honnen

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2 Comments

android.weasel Over a year ago

Thanks for the response... but my divs didn't hold any <address> elements, so why were any divs being selected? I'm a bit perplexed that contains(@class,"address") means 'if the class attribute contains the word address' but not quoting it means something... weird.

Martin Honnen Over a year ago

Your question just said you expected an error or warning in terms of an undeclared variable; there was no indication you got something selected you didn't expect to be selected; I think this is an edge case where the definition of contains says for an empty string as the second argument the result is true; and an empty node-set (which e.g. contains(@class, addresses) has as the second argument) is converted to an empty string.

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