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
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Character
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Meaning
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.
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Matches any single character
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*
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Matches zero or more occurrences of a match of the preceding character
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^
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Forces a match to the beginning of a line
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$
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A match to the end of a line
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\
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Quotes special characters
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\<
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Forces a match to the beginning of a word
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\>
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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
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Class
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Defines
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[xyz]
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Defines a character class that matches x, y, or z
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[^xyz]
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Defines a character class that matches any character except x, y, or z
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[xz]
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Defines a character class that matches any character x through z inclusive
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\(xyz\)
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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 expressions
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Expression
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Matches
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+
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Matches one or more occurrences of the preceding character
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?
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Matches zero or one occurrence of the preceding character
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(xyz)+
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Matches one or more occurrences of what xyz matches
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(xyz)?
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Matches zero or one occurrence of what xyz matches
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(xyz)*
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Matches zero or more occurrences of what xyz matches
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xyz|abc
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Matches either what xyz or what abc matches (use \| in vim)
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(xy|ab)c
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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 strings
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String
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Represents
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&
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Represents what the regular expression (search string) matched
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\n
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A quoted number, n, represents what the nth bracketed regular expression in the search string matched |
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