4 GNU Operators

Following are operators that GNU defines (and POSIX doesn't).

• Word Operators
• Buffer Operators

4.1 Word Operators

The operators in this section require Regex to recognize parts of words. Regex uses a syntax table to determine whether or not a character is part of a word, i.e., whether or not it is word-constituent.

• Non-Emacs Syntax Tables
• Match-word-boundary Operator: \b
• Match-within-word Operator: \B
• Match-beginning-of-word Operator: \<
• Match-end-of-word Operator: \>
• Match-word-constituent Operator: \w
• Match-non-word-constituent Operator: \W

4.1.1 Non-Emacs Syntax Tables

A syntax table is an array indexed by the characters in your character set. In the ASCII encoding, therefore, a syntax table has 256 elements. Regex always uses a char * variable re_syntax_table as its syntax table. In some cases, it initializes this variable and in others it expects you to initialize it.

• If Regex is compiled with the preprocessor symbols emacs and SYNTAX_TABLE both undefined, then Regex allocates re_syntax_table and initializes an element i either to Sword (which it defines) if i is a letter, number, or `_', or to zero if it's not.
• If Regex is compiled with emacs undefined but SYNTAX_TABLE defined, then Regex expects you to define a char * variable re_syntax_table to be a valid syntax table.
• See section 5.1.1 Emacs Syntax Tables, for what happens when Regex is compiled with the preprocessor symbol emacs defined.

4.1.2 The Match-word-boundary Operator (\b)

This operator (represented by `\b') matches the empty string at either the beginning or the end of a word. For example, `\brat\b' matches the separate word `rat'.

4.1.3 The Match-within-word Operator (\B)

This operator (represented by `\B') matches the empty string within a word. For example, `c\Brat\Be' matches `crate', but `dirty \Brat' doesn't match `dirty rat'.

4.1.4 The Match-beginning-of-word Operator (\<)

This operator (represented by `\<') matches the empty string at the beginning of a word.

4.1.5 The Match-end-of-word Operator (\>)

This operator (represented by `\>') matches the empty string at the end of a word.

4.1.6 The Match-word-constituent Operator (\w)

This operator (represented by `\w') matches any word-constituent character.

4.1.7 The Match-non-word-constituent Operator (\W)

This operator (represented by `\W') matches any character that is not word-constituent.

4.2 Buffer Operators

Following are operators which work on buffers. In Emacs, a buffer is, naturally, an Emacs buffer. For other programs, Regex considers the entire string to be matched as the buffer.

• Match-beginning-of-buffer Operator: \`
• Match-end-of-buffer Operator: \'

4.2.1 The Match-beginning-of-buffer Operator (\`)

This operator (represented by `\`') matches the empty string at the beginning of the buffer.

4.2.2 The Match-end-of-buffer Operator (\')

This operator (represented by `\'') matches the empty string at the end of the buffer.

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