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?

Can you elaborate in more details what did you expect to match? Everything up to last `//`? There's two of them in your string and it is not clear what you really want just from one example. — Oleg V. Volkov, Mar 24 '16 at 16:22

score 5 · Accepted Answer · answered Mar 24 '16 at 16:23

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

Also, check http://stackoverflow.com/questions/9102126/lua-return-directory-path-from-path — Wiktor Stribiżew, Mar 24 '16 at 16:28

score 3 · Answer 2 · answered Mar 24 '16 at 16:20

3

It is perfectly expected. First greedy (.+) matches as many symbols as it can without breaking following patterns - i.e. everything up to very last slash that is necessary to make ([/\\]+) match.

answered Mar 24 '16 at 16:20

Oleg V. Volkov

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Unexpected lua pattern matching result

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