[Regex-tut] Case insensitivity and local modifiers

[wtd]

Quick recap

In previous tutorials I used a set to achieve case insensitivity at the beginning on a word.

code:

/[hH]ello/

It works, but...

This works, and it's even fairly concise, but, it doesn't really indicate that case insensitivity was my goal. It also gets messier if, for instance, I wanted to make the entire word "hello" case-insensitive.

code:

/[hH][eE][lL][lL][oO]/

There's a better way?

Yes, there is. The "i" modifier can make the entire regular expression case-insensitive. It's applied in the same way as the m and x modifiers.

code:

/hello/i

Back to the future

Going back to the original example, we want only the first letter of "hello" to be case-insensitive. Fortunately, we can apply modifiers locally.

code:

/(?i:h)ello/

Similarly, modifiers can be negated locally. A rather odd reversal of the above might look like:

code:

/h(?-1:ello)/i

These two styles can be mixed.

code:

/(?i-x:h) ello /x