Regular expression live website and PHP regex trick with backslash

Regular expression is really help to process data. But a tiny typo can hardly be aware and that is why a "live" regex is really helpful for newbie as me when learning it. Below is a list of live regex for different coding language.
PHP,  phpliveregex. An important note, if you use "\\_" in php to get "\_", which means escape the first "\", you actually need "\\\\_" in the regex in PHP.
Ruby, rubular

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