| 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 charactersCharacter | Meaning |
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. | 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 | \ | Quotes 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 expressionsClass | Defines |
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[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 | [xz] | 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 in Table A-11 are special within full, or extended, regular expressions. Table A-11. Extended regular expressionsExpression | Matches |
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+ | Matches one or more occurrences of the preceding character | ? | Matches zero or one occurrence of the preceding character | (xyz)+ | Matches one or more occurrences of what xyz matches | (xyz)? | Matches zero or one occurrence of what xyz matches | (xyz)* | Matches zero or more occurrences of what xyz matches | xyz|abc | Matches either what xyz or what abc matches (use \| in vim) | (xy|ab)c | Matches 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 stringsString | Represents |
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& | 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 |
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