package main
import (
    "regexp"
    "fmt"
)
func main() {
    var re = regexp.MustCompile(`(?is)([^\?#]*\w)((?:/#|#)?)([^\?]*)($|\?.*)`)
    var str = []byte(`https://demo.wofll.com/#/demo?a=1&b=2`)
    var substitution = []byte("$1/index.html$2$3$4")
    var count = 1 // negative counter is equivalent to global case (replace all)
    
    str = re.ReplaceAllStringFunc(str, func(s string) string {
        if count == 0 {
            return s
        }
        
        count -= 1
        return re.ReplaceAllString(s, substitution)
    })
    
    fmt.Println(string(str))
}
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Golang, please visit: https://golang.org/pkg/regexp/