CODEWITHSUNDEEP
lualua-patterns
tanzil
tanzil

Reputation: 1481

Unexpected lua pattern matching result

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?

Upvotes: 4

Views: 183

Answers (2)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627468

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

Upvotes: 5

Oleg V. Volkov
Oleg V. Volkov

Reputation: 22471

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.

Upvotes: 3

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