Lua pattern parentheses and 0 or 1 occurrence

Question

I'm trying to match a string against a pattern, but there's one thing I haven't managed to figure out. In a regex I'd do this: ``` Strings: en eng engl engli englis english Pattern: ^en(g(l(i(s(h?)?)?)?)?)?$ ``` I want all strings to be a match. In Lua pattern matching I can't get this to work. Even a simpler example like this won't work: ``` Strings: fly flying Pattern: ^fly(ing)?$ ``` Does anybody know how to do this?

Accepted Answer

You can't make match-groups optional (or repeat them) using Lua's quantifiers `?`, `*`, `+` and `-`.

In the pattern `(%d+)?`, the question mark "looses" its special meaning and will simply match the literal `?` as you can see by executing the following lines of code:

```
text = "a?"
first_match = text:match("((%w+)?)")
print(first_match)
```

which will print:

```
a?
```

AFAIK, the closest you can come in Lua would be to use the pattern:

```
^eng?l?i?s?h?$
```

which (of course) matches string like `"enh"`, `"enls"`, ... as well.

Lua pattern parentheses and 0 or 1 occurrence

Solution

Problem