GNU sed Regular Expression Extensions
With the -r option, GNU sed uses Extended Regular Expressions instead of Basic Regular expressions. (See Chapter 7 for more information.) However, even without -r, you can use additional escape sequences for more powerful text matching. The following escape sequences are valid only in regular expressions:
- \b
Matches on a word boundary, where of the two surrounding characters (x\by), one is a word-constituent character and the other is not.
- \B
Matches on a nonword boundary, where both of the two surrounding characters (x\by) are either word-constituent or not word-constituent.
- \w
Matches any word-constituent character (i.e., a letter, digit, or underscore).
- \W
Matches any nonword-constituent character (i.e., anything that is not a letter, digit, or underscore).
- \'
Matches the beginning of the pattern space. This is different from ^ when the m modifier is used for a pattern or the s command.
- \'
Matches the end of the pattern space. This is different from $ when the m modifier is used for a pattern or the s command.
The following escape sequences may be used anywhere.
- \a
The ASCII BEL character.
- \f
The ASCII formfeed character.
- \n
The ASCII newline character.
- \r
The ASCII carriage-return character.
- \v
The ASCII vertical tab character.
- \dnn
The character whose ASCII decimal value is nn.
- \onn
The character whose ASCII octal value is nn.
- \xnn
The character whose ASCII hexadecimal value is nn.
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