What are dangling metacharacters in regex?

问题

In Ruby, I wrote a simple regex to find the first {:

txt.gsub! /^.*{/, '{'

Whenever I run this, everything past that point for my purposes works fine, however there is a mild error that reads along the lines of WARNING: Dangling metacharacter detected. What specifically are dangling metacharacters, and how would I change my regex to be as explicit and efficient as possible?

回答1:

{ has special meaning in regular expression.

PATTERN{m,n}

Above matches PATTERN repeated m~n times.

If you want avoid that warning (to match literally match {) escape it.

txt.gsub! /^.*\{/, '{'

UPDATE

BTW, /^.*{/ does not catch the first { because .* is greedy match; It consume as much as possible.

来源：https://stackoverflow.com/questions/20585639/what-are-dangling-metacharacters-in-regex