How do you parse a regex to key-value pairs in Lua?

Parsing a regex to key-value pairs in Lua typically involves using Lua's string manipulation functions along with pattern matching. Here's a breakdown of how you can achieve this:

1. Understanding the Regex and Desired Format:

- First, you need to define the regex pattern that matches your key-value pairs. For example, if your string is in the format key1=value1;key2=value2;..., your regex should capture the key and value parts.

2. Using Lua's `string.gmatch` Function:

- The `string.gmatch` function is perfect for iterating over all matches of a pattern in a string. It returns an iterator that yields the captured values.

3. Example Code:

function parse_key_value_pairs(input_string, pattern)
  local result = {}
  for key, value in string.gmatch(input_string, pattern) do
    result[key] = value
  end
  return result
end

-- Example usage:
local input = "name=John Doe;age=30;city=New York"
local pattern = "(%w+)=(%w+)"
local key_value_pairs = parse_key_value_pairs(input, pattern)

for key, value in pairs(key_value_pairs) do
  print(key, value)
end

4. Explanation:

- The `parse_key_value_pairs` function takes the input string and the regex pattern as arguments.

- It initializes an empty table `result` to store the key-value pairs.

- The `string.gmatch` function iterates over all matches of the pattern in the input string. The pattern (%w+)=(%w+) captures one or more word characters (%w+) as the key and one or more word characters as the value, separated by an equals sign.

- For each match, the captured key and value are added to the `result` table.

- Finally, the function returns the `result` table.

5. Handling More Complex Values:

- If your values can contain spaces or other special characters, you might need to adjust the regex pattern. For example, ([^=]+)=([^;]+);? would capture any characters up to the next equals sign as the key and any characters up to the next semicolon as the value. The ;? makes the semicolon optional at the end of the string.

6. Error Handling:

- You might want to add error handling to check if the input string matches the expected format or if the regex pattern is valid.

By using this approach, you can effectively parse a regex to key-value pairs in Lua, making it easy to extract structured data from strings.

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