Coyote Point Systems E350GX, Руководство по установке и администрированию

Страница: 278 / 344

Appendix D: Regular Expression Format
274 Equalizer Installation and Administration Guide
• A bracket expression.
• A period (.), which matches any single character.
• A carat (^), which matches the null string at the beginning of a line.
• A dollar sign ($), which matches the null string at the end of a line.
• A backslash (\) followed by one of the following characters: ^.[$()|*+?{\, which matches that character
taken as an ordinary character.
• A backslash (\) followed by any other character, which matches that character taken as an ordinary
character (as if the \ had not been present).
• A single character with no other significance, which simply matches that character. Note that regular
expressions are case-insensitive.
• An open brace ({) followed by a character other than a digit is an ordinary character, not the beginning of a
bound. It is illegal to end a real expression with a backslash (\).
Creating a Bracket Expression
A bracket expression is a list of characters enclosed in brackets ( [...] ). It normally matches any single character
from the list. If the list begins with ^, it matches any single character not from the rest of the list. Two characters in a
list that are separated by '-' indicates the full range of characters between those two (inclusive) in the collating
sequence; for example, '[0-9]' in ASCII matches any decimal digit. It is illegal for two ranges to share an endpoint;
for example, 'a-c-e'. Ranges are very collating-sequence-dependent, and portable programs should avoid relying on
them.
• To include a literal ']' in the list, make it the first character (following an optional '^').
• To include a literal '-', make it the first or last character, or the second endpoint of a range.
• To use a literal '-' as the first endpoint of a range, enclose it in '[.' and '.]' to make it a collating element (see
below).
With the exception of these and some combinations using '[' (see next paragraphs), all other special characters,
including '\', lose their special significance within a bracket expression.
Within a bracket expression, a collating element (a character, a multi-character sequence that collates as if it were a
single character, or a collating-sequence name for either) enclosed in '[.' and '.]' stands for the sequence of characters
of that collating element. The sequence is a single element of the bracket expression's list. A bracket expression
containing a multi-character collating element can thus match more than one character; e.g., if the collating sequence
includes a 'ch' collating element, then the real expression '[[.ch.]]*c' matches the first five characters of 'chchcc'.
Within a bracket expression, a collating element enclosed in '[' and `]' is an equivalence class, representing the
sequences of characters of all collating elements equivalent to that one, including itself. (If there are no other
equivalent collating elements, the treatment is as if the enclosing delimiters were '[.' and '.]'.) For example, if 'x' and
'y' are the members of an equivalence class, then '[[x]]', '[[y]]', and '[xy]' are all synonymous. An equivalence class
may not be an end-point of a range.
Within a bracket expression, the name of a character class enclosed in '[:' and ':]' stands for the list of all characters
belonging to that class.
There are two special cases of bracket expressions: the bracket expressions '[[:<:]]' and '[[:>:]]' match the null string
at the beginning and end of a word respectively. A word is defined as a sequence of word characters that is neither
preceded nor followed by word characters. A word character is an alnum character (as defined by ctype(3)) or an
underscore. This is an extension, compatible with but not specified by IEEE Std 1003.2 (''POSIX.2''), and should be
used with caution in software intended to be portable to other systems.