How to match a regex with backreference in Go?

Question

I need to match a regex that uses backreferences (e.g. \\1) in my Go code.

That\'s not so easy because in Go, the official regexp package uses the RE2 engine, one th

Answer 1

When I had the same problem, I solved it using a two-step regular expression match. The original code is:

if m := match(pkgname, `^(.*)\$\{DISTNAME:S(.)(\\^?)([^:]*)(\\$?)\2([^:]*)\2(g?)\}(.*)$`); m != nil {
    before, _, left, from, right, to, mod, after := m[1], m[2], m[3], m[4], m[5], m[6], m[7], m[8]
    // ...
}

The code is supposed to parse a string of the form ${DISTNAME:S|from|to|g}, which itself is a little pattern language using the familiar substitution syntax S|replace|with|.

The two-stage code looks like this:

if m, before, sep, subst, after := match4(pkgname, `^(.*)\$\{DISTNAME:S(.)([^\\}:]+)\}(.*)$`); m {
    qsep := regexp.QuoteMeta(sep)
    if m, left, from, right, to, mod := match5(subst, `^(\^?)([^:]*)(\$?)`+qsep+`([^:]*)`+qsep+`(g?)$`); m {
        // ...
    }
}

The match, match4 and match5 are my own wrapper around the regexp package, and they cache the compiled regular expressions so that at least the compilation time is not wasted.