string substr(string string, int start, int [length]);Substr returns the portion of string specified by the start and length parameters.
If start is positive, the returned string will start at the start'th character of string.
If start is negative, the returned string will start at the start'th character from the end of string.
If length is given and is positive, the string returned will end length characters from start. If this would result in a string with negative length, then the returned string will contain the single character at start.
If length is given and is negative, the string returned will end length characters from the end of string. If this would result in a string with negative length, then the returned string will contain the single character at start.