Lazy matching using ? not enabled in bracketed subexpressions

[nalimilan]

This is something I experienced using R, which includes a copy of TRE which dates back to 2009. Sorry if it has been fixed since then.

The idea is that I want to remove the inner tag in the following expression, while keeping the outer one. I do not know beforehand what may appear in the tags after "class=" and "style=".

"ab"

Thus, the expected result is:

"ab"

The expression I tried is the following, and it works with PCRE. With TRE, the first .* is always greedy:

(gsub() matches the first pattern against the third string and replaces them with the second pattern.)

gsub("(?U)(._)", "\1", "ab")
[1] "b"

gsub("(._?)", "\1", "ab")
[1] "b"

// Use PCRE instead of TRE

gsub("(._?)", "\1", "ab", perl=TRUE)
[1] "ab"

Moreover, it looks like the parentheses around the second .* change the result:

gsub("(._?)", "", "ab")
[1] ""

gsub("._?", "", "ab")
[1] "b"

gsub("(?U)(._)", "", "ab")
[1] ""

gsub("(?U)._", "", "ab")
[1] "b"