APPENDIX 7 - REGULAR EXPRESSIONS IN THE

THE uses the GNU Regular Expression Library to implement regular expressions. This library has several different regular expression syntaxes that can be used when specifying targets.

Note that all pattern specifications used for syntax highlighting always uses the EMACS regular expression syntax.

The following table lists the features of each of the regular expression syntaxes that can be set via the SET REGEXP command. Each feature in the table is explained later.

This appendix is not intended to explain everything about regular expressions. If you want to find out more about GNU Regular Expressions, then view the on-line documentation at http://www.hessling-editor.sf.net/doc/regex/regex/ .

BACKSLASH_ESCAPE_IN_LISTS

If this feature is not set, then \ inside a bracket expression is literal.
If set, then such a \ quotes the following character.

BACKSLASH_PLUS_QM

If this feature is not set, then + and ? are operators, and \+ and \? are literals.
If set, then \+ and \? are operators and + and ? are literals.

CHAR_CLASSES

If this feature is set, then character classes are supported. They are:
[:alpha:], [:upper:], [:lower:], [:digit:], [:alnum:], [:xdigit:], [:space:], [:print:], [:punct:], [:graph:], and [:cntrl:].
If not set, then character classes are not supported.

CONTEXT_INDEP_ANCHORS

If this feature is set, then ^ and $ are always anchors (outside bracket expressions, of course).
If this feature is not set, then it depends:
^ is an anchor if it is at the beginning of a regular expression or after an open-group or an alternation operator;
$ is an anchor if it is at the end of a regular expression, or before a close-group or an alternation operator.

This feature could be (re)combined with CONTEXT_INDEP_OPS, because POSIX draft 11.2 says that * etc. in leading positions is undefined.

CONTEXT_INDEP_OPS

If this feature is set, then special characters are always special regardless of where they are in the pattern.
If this feature is not set, then special characters are special only in some contexts; otherwise they are ordinary. Specifically, * + ? and intervals are only special when not after the beginning, open-group, or alternation operator.

CONTEXT_INVALID_OPS

If this feature is set, then *, +, ?, and { cannot be first in an RE or immediately after an alternation or begin-group operator.

DOT_NEWLINE

If this feature is set, then . matches newline. If not set, then it does not.

DOT_NOT_NULL

If this feature is set, then . does not match NUL. If not set, then it does.

HAT_LISTS_NOT_NEWLINE

If this feature is set, nonmatching lists [^...] do not match newline. If not set, they do.

INTERVALS

If this feature is set, either \{...\} or {...} defines an interval, depending on NO_BACKSLASH_BRACES.
If not set, \{, \}, {, and } are literals.

LIMITED_OPS

If this feature is set, +, ? and | are not recognized as operators. If not set, they are.

NEWLINE_ALT

If this feature is set, newline is an alternation operator. If not set, newline is literal.

NO_BACKSLASH_BRACES

If this feature is set, then `{...}' defines an interval, and \{ and \} are literals. If not set, then `\{...\}' defines an interval.

NO_BACKSLASH_PARENS

If this feature is set, (...) defines a group, and \( and \) are literals. If not set, \(...\) defines a group, and ( and ) are literals.

NO_BACKSLASH_REFS

If this feature is set, then \ matches . If not set, then \ is a back-reference.

NO_BACKSLASH_VBAR

If this feature is set, then | is an alternation operator, and \| is literal. If not set, then \| is an alternation operator, and | is literal.

NO_EMPTY_RANGES

If this feature is set, then an ending range point collating higher than the starting range point, as in [z-a], is invalid.
If not set, then when ending range point collates higher than the starting range point, the range is ignored.

UNMATCHED_RIGHT_PAREN_ORD

If this feature is set, then an unmatched ) is ordinary. If not set, then an unmatched ) is invalid.