Parsing regex with alternatives and optionals

问题

I'm building a chatbot subset of RiveScript and trying to build the pattern matching parser with regular expression. Which three regexes match the following three examples?

ex1: I am * years old
valid match:
- "I am 24 years old"
invalid match:
- "I am years old"

ex2: what color is [my|your|his|her] (bright red|blue|green|lemon chiffon) *
valid matches:
- "what color is lemon chiffon car"
- "what color is my some random text till the end of string"

ex3: [*] told me to say *
valid matches:
- "Bob and Alice told me to say hallelujah"
- "told me to say by nobody"

The wildcards mean any text that is not empty is acceptable.

In example 2, anything between [ ] is optional, anything between ( ) is alternative, each option or alternative is separated by a |.

In example 3, the [*] is an optional wildcard, meaning blank text can be accepted.

回答1:

1. https://regex101.com/r/CuZuMi/4

   I am (?:\d+) years old
   

2. https://regex101.com/r/CuZuMi/2

   what color is.*(?:my|your|his|her).*(?:bright red|blue|green|lemon chiffon)?.*
   

3. https://regex101.com/r/CuZuMi/3

   .*told me to say.*
   

---

I am using mostly 2 things:

1. (?:) non-capture groups, to group things together like the parenthesis use on math.
2. .* match any character 0 or more times. Could be replaced by {1,3} to match between 1 and 3 times.

You can exchange * by + to match at least 1 character, instead of 0. And the ? after the non-capture group, makes that group optional.

---

These are golden place for you to start:

1. http://www.rexegg.com/regex-quickstart.html
2. https://regexone.com/
3. http://www.regular-expressions.info/quickstart.html
4. Reference - What does this regex mean?

来源：https://stackoverflow.com/questions/42464120/parsing-regex-with-alternatives-and-optionals