Finding '.' with string.find()

Question

I'm trying to make a simple string manipulation: getting the a file's name, without the extension. Only, string.find() seem to have an issue with dots:

s = 'crate.png'
i, j = string.find(s, '.')
print(i, j) --> 1 1

And only with dots:

s = 'crate.png'
i, j = string.find(s, 'p')
print(i, j) --> 7 7

Is that a bug, or am I doing something wrong?

Solution 1

string.find(), by default, does not find strings in strings, it finds patterns in strings. More complete info can be found at the link, but here is the relevant part;

The '.' represents a wildcard character, which can represent any character.

To actually find the string ., the period needs to be escaped with a percent sign, %.

EDIT: Alternately, you can pass in some extra arguments, find(pattern, init, plain) which allows you to pass in true as a last argument and search for plain strings. That would make your statement;

> i, j = string.find(s, '.', 1, true)   -- plain search starting at character 1
> print(i, j) 
6 6

Solution 2

Do either string.find(s, '%.') or string.find(s, '.', 1, true)

Solution 3

The other answers have already explained what's wrong. For completeness, if you're only interested in the file's base name you can use string.match. For example:

string.match("crate.png", "(%w+)%.")  --> "crate"

Comments

[Rohan Desai]

-1; The escape character for Lua patterns is %, not \ . Trying to use a backslash will probably give you an "invalid escape sequence" error.

[Joachim Isaksson]

@missingno You're of course correct, I mixed up the escape character for escape sequences and patterns. Fixed the answer.