User:Merlin11188/Draft

Patterns

Patterns require some knowledge of string manipulation.

Classes

Character Class:

A character class is used to represent a set of characters. The following are character classes and their representations:

• x — Where x is any non-magic character (^$()%.[]*+-?), x represents itself
• . — Represents all characters (#32kas321fslk#?@34)
• %a — Represents all letters (aBcDeFgHiJkLmNoPqRsTuVwXyZ)
• %c — Represents all control characters (all ascii characters below 32 and ascii character 127)
• %d — Represents all base-10 digits (1-10)
• %l — Represents all lower-case letters (abcdefghijklmnopqrstuvwxyz)
• %p — Represents all punctuation characters (#^;,.) etc.
• %s — Represents all space characters
• %u — Represents all upper-case letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
• %w — Represents all alpha-numeric characters (aBcDeFgHiJkLmNoPqRsTuVwXyZ0123456789)
• %x — Represents all hexadecimal digits (0123456789ABCDEF)
• %z — Represents the character with representation 0 (the null terminator)
• %x — Represents (where x is any non-alphanumeric character) 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. So, a percent sign in a string is "%%"
  

Here's an example:

Example

String="Ha! You'll never find any of these (323414123114452) numbers inside me!"
print(string.match(String, "%d")) -- Find a digit character

Output:
3

An upper-case version of any of these classes results in the complement of that class. For instance, %A will represent all non-letter characters. Here's another example:

Example

Martian="141341432431413415072343E234141241312"
print(Martian:match("%D")) -- Find a non-digit character

Output:
E

Modifiers

In Lua, there are 4 modifiers:

• + — 1 or more repetitions
• * — 0 or more repetitions
• - — also 0 or more repetitions
• ? — optional (0 or 1 occurrence)

• [set] represents the class which is the union of all characters in set. A range of characters may be specified by separating the end characters of the range with a '-'. All classes %x described above may 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.

The interaction 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 may be

• a single character class, which matches any single character in the class;
• a single character class followed by '*', which matches 0 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
• a single character class followed by '+', which matches 1 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
• a single character class followed by '-', which also matches 0 or more repetitions of characters in the class. Unlike '*', these repetition items will always match the shortest possible sequence;
• a single character class followed by '?', which matches 0 or 1 occurrence of a character in the class;
• %n, for n between 1 and 9; such item matches a substring equal to the n-th captured string (see below);
• %bxy, where x and y are two distinct characters; such item matches strings that start with x, end with y, and where the x and y are balanced. This means that, if one reads the string from left to right, counting +1 for an x and -1 for a y, the ending y is the first y where the count reaches 0. For instance, the item %b() matches expressions with balanced parentheses.

Pattern:

A pattern is a sequence of pattern items. A '^' at the beginning of a pattern anchors the match at the beginning of the subject string. A '$' at the end of a pattern anchors the match at the end of the subject string. At other positions, '^' and '$' have no special meaning and represent themselves. Captures:

A pattern may contain sub-patterns enclosed in parentheses; they describe captures. When a match succeeds, the substrings of the subject string that match captures are stored (captured) for future use. Captures are numbered according to their left parentheses. For instance, in the pattern "(a*(.)%w(%s*))", the part of the string matching "a*(.)%w(%s*)" is stored as the first capture (and therefore has number 1); the character matching "." is captured with number 2, and the part matching "%s*" has number 3.

As a special case, the empty capture () captures the current string position (a number). For instance, if we apply the pattern "()aa()" on the string "flaaap", there will be two captures: 3 and 5.

A pattern cannot contain embedded zeros. Use %z instead.