Ruby中如何替换多个正则表达式各自的首次匹配项

这问题我之前也碰到过，刚好给你捋清楚～你想要的是每个目标名字各自的首次出现被替换成加粗格式，而不是全局替换所有实例，也不是只替换第一个匹配到的任意名字，对吧？

核心思路 #

既然sub方法只会替换当前字符串中第一个匹配到的目标，那我们可以逐个处理每个目标名字，对每个名字单独调用sub，这样就能保证每个名字只被替换第一次出现的位置，后续的出现会被保留。

具体实现代码 #

names_hash = {"Lebron James" => "**Lebron James**", "Chris Paul" => "**Chris Paul**"}
str = "of the best players left in the playoffs, Lebron James is the most experienced player left in the field and probably in all of the league. Chris Paul has played in many playoff games but has never been to a conference final. Lebron James on the other hand, has been to seven straight NBA finals."

# 遍历每个名字，逐个替换首次出现
names_hash.each do |name, replacement|
  str = str.sub(name, replacement)
end

puts str

如果你喜欢更简洁的写法，也可以用inject来链式处理：

result = names_hash.inject(str) do |current_str, (name, replacement)|
  current_str.sub(name, replacement)
end

puts result

结果验证 #

运行上面的代码后，输出的结果正好符合你的预期：

"of the best players left in the playoffs, Lebron James is the most experienced player left in the field and probably in all of the league. Chris Paul has played in many playoff games but has never been to a conference final. Lebron James on the other hand, has been to seven straight NBA finals."

为什么原来的方法不行？ #

• 用str.sub(regex, names_hash)时，正则会匹配到第一个符合条件的字符串（也就是开头的Lebron James），替换一次就停止了，根本不会处理Chris Paul的首次出现；
• 用str.gsub(regex, names_hash)则会替换所有匹配到的实例，包括Lebron James的第二次出现，这也不符合你的需求。

内容的提问来源于stack exchange，提问作者fhbi