Here s what I m using: ".+/@[^/]+$". Can you think of a reason why this might not work?
This is actually a very subtle problem and I think a great question.
My understanding is that an (abbreviated) XPATH points to an attribute if and only its last @ is not within a predicate, that is, something of the form [...], and has no steps after it (something like /...). I think this has the relatively simple regular expression @[^]/]*$, that is, there must be an @ that has no ]s nor /s after it. Also, if you want to cover unabbreviated XPATHs, you can use (@|attribute::)[^]/]*$
I ve included a test harness that may prove useful in checking this or other tests. Note also that there may be whitespace in between tokens which can complicate some regexs.
@* or @a or ../@a or a/@ba[@b and @c]/@da[b[@c="d"]/e[@f and @g]]/h[@i="j"]/@ka[@b] or a[@b and @c]a[b[@c and @d]/@e]a[b[@c="d"]/e[@f and @g]]/h[@i="j"]/k[5][@l="m"]I can t think of a legal example where there is a / but not a ] after the last example, but I think there might be one.
Hopefully these examples make it at least a little clear that there can be arbitrary nesting of [ and ] together with @s anywhere in between. Luckily, I think only the very last @ and its nesting level matters.
(For reference, the OP s regex fails on @a. My original regex failed on a[@b and @c].)
Edit: It turns out that there are more corner cases, which convinces me that there is no perfectly-correct regular expression. For example, once you have an attribute node, there are many ways of keeping it, e.g. //@a// or //@a/. in the abbreviated syntax. There are also a variety of more creative ways, such as //@f//[node()]. All in all, it seems that if you want to cover these cases, you need to be able to match [ and ], which a basic regular expression cannot do. On the other hand, you could decide this is too contrived ...
Recently I discovered two amazing regular expression features: ?: and ?!. I was curious of other neat regex features. So maybe you would like to share some tricky regular expressions.
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