Patterns
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 inset. A range of characters can bespecified 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] representsthe 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 ofset,
wheresetis 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 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 can 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 firstcapture (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.