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particular, the callstring.sub(s,1,j) returns a prefix of s with length j, and string.sub(s, -i) returns
a suffix of s with length i.
string.upper (s)
Receives a string and returns a copy of this string with all lowercase letters changed to
uppercase. All other characters are left unchanged. The definition of what a lowercase letter is
depends on the current locale.
Patterns
Character Class:
A character class is used to represent a set of characters. The following combinations are
allowed in describing a character class:
x: (where x is not one of the magic characters ^$()%.[]*+-?) represents the character x
itself.
.: (a dot) represents all characters.
%a: represents all letters.
%c: represents all control characters.
%d: represents all digits.
%l: represents all lowercase letters.
%p: represents all punctuation characters.
%s: represents all space characters.
%u: represents all uppercase letters.
%w: represents all alphanumeric characters.
%x: represents all hexadecimal digits.
%z: represents the character with representation 0.
%x: (where x is any non-alphanumeric character) represents the character x. This is the
standard way to escape the magic characters. Any punctuation character (even the non
magic) can be preceded by a '%' when used to represent itself in a pattern.
[set]: represents the class which is the union of all characters in set. A range of
characters can be specified by separating the end characters of the range with a '-'. All
classes %x described above can also be used as components in set. All other characters
in set represent themselves. For example,[%w_] (or [_%w]) represents all alphanumeric
characters plus the underscore, [0-7] represents the octal digits, and [0-7%l%-]
represents the octal digits plus the lowercase letters plus the '-'character.
on between ranges and classes is not defined. Therefore, patterns like
[%a-z]or [a-%%] have no meaning.
[^set]: represents the complement of set, where set is interpreted as above.
For all classes represented by single letters (%a, %c, etc.), the corresponding uppercase letter
represents the complement of the class. For instance, %S represents all non-space characters.
The definitions of letter, space, and other character groups depend on the current locale. In
particular, the class [a-z] may not be equivalent to %l.
Pattern Item:
A pattern item can be:
characters in the class. These repetition items will always match the longest possible
sequence;
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