Character class can be used to match a single character out of several possible characters. Alternation is more generic than character class. It can also be used to match an expression out of several possible expressions.
+ +In the above example, cat|dog|lion basically means 'either cat or dog or lion'. Here, we have used specific expression(cat, dog & lion), but we can use any regular expression. For example,
boot|bot, b(o|oo)t. Last expression is using a group.Suppose, you want to match two words Set and SetValue. What will be the regular expression?
+ +From whatever we have learned so far, you will say, Set|SetValue will be the answer. But it is not correct.
If you try SetValue|Set, then it is working.
Can you observe anything from it?
+ +OR operator tries to match a substring starting from the first word(or expression)-in the regex. If it is a match, then it will not try to match the next word(or expression) at the same place in text.
+ +Find out an regex which matches each and every word in the following set: {bat, cat, hat, mat, nat, oat, pat, Pat, ot}. The regex should be as small as possible.
Hint: Use character-class, ranges and or-operator together.
+ +Answer: [b-chm-pP]at|ot