Manuale_LUA

a number

For non-integral numeric types, causes the decimal portion of the output to be expressed in at least number digits. For the string type, causes the output to be truncated at number characters. If the precision is zero, nothing is printed for the corresponding argument.

*

Same as the above, but uses an integer value in the intaken argument to determine the number of decimal places or maximum string length. For example, printf("%.*s", 3, "abcdef") will result in "abc" being printed.