Regex - Trimming whitespace from start and end of line [closed]

Question

Link: http://regexone.com/example/5

It asks: Write a simple regular expression to capture the content of each line, without the extra whitespace.

What I have is a mess with a bunch of \S+, is there an elegant way to solve this problem?

Answer 1

Writing regular expressions may seem like a black art, but it's actually quite simple; the most important step is to identify with surgical precision exactly what you do and do not want to match, then say just what you mean (no more and no less).

Another tip: when using * or + qualifiers, especially with "wildcard" characters like ., always remember that part of the regex may "run past" the part which you wanted to match, perhaps matching the entire string. Often, the simplest solution is to use a reluctant qualifier like *? or +? instead. (The most common regexp bugs are those which make the regexp match when you didn't want it to or more than you wanted to.)

In this case, you want "the content of each line, without extra whitespace". That's not quite precise enough. What is "extra whitespace"? Trailing and leading whitespace? If so...

Let's express that in completely precise, non-ambiguous terms. What you basically have is:

1. A region of whitespace characters (possibly empty)
2. Either: a) Nothing. b) A single non-whitespace character. c) A region which starts and ends with non-whitespace characters.
3. A region of whitespace characters (possibly empty)

Can you express that as a regex? Try doing so and posting it here, then I'll give you some feedback.