Unexpected lua pattern matching result

Question

For the following code:

local function getParentPath(_path)

    pattern = "(.+)([/\\][/\\])(.+)"
    i,j,k = string.match(path,pattern)
    return i,j,k

end

print(getParentPath(path))

For path = "C://data//file.text", I get:

C://data // file.text

But For path = "C:\data\file.text", I get:

nil nil nil

I am looking for a pattern which woks for both. Any suggestions?

Answer 1

The problem is that the first .+ matches greedily and grabs all up to the last \ and then backtracks. Then, one \ can be matched with [\\/], and thus the first group has one backslash, and the second has got the second.

You can fix it by using

pattern = "^(.-)([/\\]+)([^/\\]+)$"

See IDEONE demo

Explanation:

• ^ - start of string
• (.-) - any characters but as few as possible (lazy matching with - quantifier)
• ([/\\]+) - 1+ / or \
• ([^/\\]+) - 1+ characters other than / and \
• $ - end of string