Appendix Summary

A regular expression defines a set of one or more strings of characters. A regular expression is said to match any string it defines.

In a regular expression, a special character is one that does not represent itself. Table A-9 lists special characters.

Table A-9. Special characters

Character	Meaning
.	Matches any single character
*	Matches zero or more occurrences of a match of the preceding character
^	Forces a match to the beginning of a line
$	A match to the end of a line
\	Used to quote special characters
\ <	Forces a match to the beginning of a word
\ >	Forces a match to the end of a word

Table A-10 lists ways of representing character classes and bracketed regular expressions.

Table A-10. Character classes and bracketed regular expressions

Class	Defines
[xyz ]	Defines a character class that matches x, y, or z
[^ xyz ]	Defines a character class that matches any character except x, y, or z
[x z ]	Defines a character class that matches any character x through z inclusive
\ ( xyz \ )	Matches what xyz matches (a bracketed regular expression)

In addition to the preceding special characters and strings (excluding quoted parentheses, except in vim), the characters given in Table A-11 are special within full, or extended, regular expressions.

Table A-11. Extended regular expressions

Expression	Matches
+	Matches one or more occurrences of the preceding character
?	Matches zero or one occurrence of the preceding character
(xyz )+	One or more occurrences of what xyz matches
(xyz )?	Zero or one occurrence of what xyz matches
(xyz )*	Zero or more occurrences of what xyz matches
xyz |abc	Either what xyz or what abc matches (use \| in )
(xy |ab)c	Either what xyc or what abc matches (use \| in vim)

Table A-12 lists characters that are special within a replacement string in sed and vim.

Table A-12. Replacement strings

String	Represents
&	Represents what the regular expression (search string) matched
\n	A quoted number, n, represents what the nth bracketed regular expression in the search string matched