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lualua-patterns

Pattern match dropping new lines characters

How to extract the values from a csv like string dropping the new lines characters (\r\n or \n) with a pattern.

A line looks like:

1.1;2.2;Example, 3

Notice there are only 3 values and the separator is ;. The problem I'm having is to come up with a pattern that reads the values while dropping the new line characters (the file comes from a windows machine so it has \r\n, reading it from a linux and would like to be independent from the new line character used).

My simple example right now is:

s = "1.1;2.2;Example, 3\r\n";
p = "(.-);(.-);(.-)";
a, b, c = string.match(s, p);
print(c:byte(1, -1));

The two last characters printed by the code above are the \r\n.

The problem is that both, \r and \n are detected by the %c and %s classes (control characters and space characters), as show by this code:

s = "a\r";
print(s:match("%c"));
print(s:match("%s"));
print(s:match("%d"));

So, is it possible to left out from the match the new lines characters? (It should not be assumed that the last two characters will be new lines characters)

The 3º value may contain spaces, punctuation and alphanumeric characters and since \r\n are detected as space characters a pattern like `"(.-);(.-);([%w%s%c]-).*" does not work.

Solution

  • Your pattern

    p = "(.-);(.-);(.-)";

    does not work: the third field is always empty because .- matches a little as possible. You need to anchor it at the end of the string, but then the third field will contain trailing newline chars:

    p = "(.-);(.-);(.-)$";

    So, just stop at the first trailing newline char. This also anchors the last match. Try this pattern instead:

    p = "(.-);(.-);(.-)[\r\n]";

    If trailing newline chars are optional, try this pattern:

    p = "(.-);(.-);(.-)[\r\n]*$";