PATTERNS(7) FreeBSD Miscellaneous Information Manual PATTERNS(7)
NAME
patterns - Lua's pattern matching rules
DESCRIPTION
Pattern matching in httpd(8) is based on the implementation of the Lua
scripting language and provides a simple and fast alternative to the
regular expressions (REs) that are described in re_format(7). Patterns
are described by regular strings, which are interpreted as patterns by
the pattern-matching "find" and "match" functions. This document
describes the syntax and the meaning (that is, what they match) of these
strings.
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.
%g represents all printable characters except space.
%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.
%x (where x is any non-alphanumeric character) represents the
character x. This is the standard way to escape the magic
characters. Any non-alphanumeric character (including all
punctuation characters, even the non-magical) 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, in ascending order, 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.
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 can be
o a single character class, which matches any single character in the
class;
o a single character class followed by `*', which matches zero or more
repetitions of characters in the class. These repetition items will
always match the longest possible sequence;
o a single character class followed by `+', which matches one or more
repetitions of characters in the class. These repetition items will
always match the longest possible sequence;
o a single character class followed by `-', which also matches zero or
more repetitions of characters in the class. Unlike `*', these
repetition items will always match the shortest possible sequence;
o a single character class followed by `?', which matches zero or one
occurrence of a character in the class. It always matches one
occurrence if possible;
o `%n', for n between 1 and 9; such item matches a substring equal to
the n-th captured string (see below);
o `%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.
o `%f[set]', a frontier pattern; such item matches an empty string at
any position such that the next character belongs to set and the
previous character does not belong to set. The set set is
interpreted as previously described. The beginning and the end of
the subject are handled as if they were the character `\0'.
PATTERN
A pattern is a sequence of pattern items. A caret `^' 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 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: 2 and 4.
SEE ALSO
fnmatch(3), re_format(7), httpd(8)
Roberto Ierusalimschy, Luiz Henrique de Figueiredo, and Waldemar Celes,
Patterns, Lua 5.3 Reference Manual,
https://www.lua.org/manual/5.3/manual.html#6.4.1, Lua.org, PUC-Rio, June
2015.
HISTORY
The first implementation of the pattern rules were introduced with Lua
2.5. Almost twenty years later, an implementation based on Lua 5.3.1
appeared in OpenBSD 5.8.
AUTHORS
The pattern matching is derived from the original implementation of the
Lua scripting language written by Roberto Ierusalimschy, Waldemar Celes,
and Luiz Henrique de Figueiredo at PUC-Rio. It was turned into a native
C API for httpd(8) by Reyk Floeter <
[email protected]>.
CAVEATS
A notable difference with the Lua implementation is the position in the
string returned by captures. It follows the C-style indexing (position
starting from 0) instead of Lua-style indexing (position starting from
1).
FreeBSD 14.1-RELEASE-p8 November 8, 2023 FreeBSD 14.1-RELEASE-p8