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 Chapter 6Pattern Matching

## 6.3 Metacharacters

The characters below have special meaning only in search patterns:

 . Match any single character except newline. * Match any number (or none) of the single character that immediately precedes it. The preceding character can also be a regular expression. E.g., since ``` .``` (dot) means any character, ``` .*``` means "match any number of any character." ^ Match the following regular expression at the beginning of the line. \$ Match the preceding regular expression at the end of the line. [ ] Match any one of the enclosed characters. A hyphen (``` -``` ) indicates a range of consecutive characters. A circumflex (``` ^``` ) as the first character in the brackets reverses the sense: it matches any one character not in the list. A hyphen or close bracket (``` ]``` ) as the first character is treated as a member of the list. All other metacharacters are treated as members of the list. ``` \{ ``` ``` n ``` ,``` m ``` ``` \} ``` Match a range of occurrences of the single character that immediately precedes it. The preceding character can also be a regular expression. \{ n \} matches exactly n occurrences, \{ n \} matches at least n occurrences, and \{ n , m \} matches any number of occurrences between n and m . n and m must be between 0 and 256, inclusive. \ Turn off the special meaning of the character that follows. ``` \( \) ``` Save the pattern enclosed between \( and \) into a special holding space. Up to nine patterns can be saved on a single line. They can be "replayed" in substitutions by the escape sequences \1 to \9. ``` \< \> ``` Match characters at beginning (\<) or end (\>) of a word. ``` + ``` Match one or more instances of preceding regular expression. ``` ? ``` Match zero or one instances of preceding regular expression. ``` | ``` Match the regular expression specified before or after. ``` ( ) ``` Apply a match to the enclosed group of regular expressions.

The characters below have special meaning only in replacement patterns.

 \ Turn off the special meaning of the character that follows. \``` n ``` Restore the n th pattern previously saved by \( and \). n is a number from 1 t 9, with 1 starting on the left. & Reuse the search pattern as part of the replacement pattern. ~ Reuse the previous replacement pattern in the current replacement pattern. ``` \u ``` Convert first character of replacement pattern to uppercase. ``` \U ``` Convert replacement pattern to uppercase. ``` \l ``` Convert first character of replacement pattern to lowercase. ``` \L ``` Convert replacement pattern to lowercase.

 6.2 Metacharacters, Listed by UNIX Program 6.4 Examples of Searching