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Appendix A: Regular Expressions

Appendix A. Regular Expressions

The following table lists special characters in regular expressions and their meanings.

TypeDescriptionExample
^Beginning of input or line ^T matches “T” in “This good earth” but not in “Uncle Tom.”
$End of input or line h$ matches “h” in “teach” but not in “teacher.”
*The preceding character 0 or more times um* matches “um” in “rum,” “umm” in “yummy,” and “u” in “huge.”
+The preceding character 1 or more times um+ matches “um” in “rum” and “umm” in “yummy.”
?The preceding character at most once st?on matches “son” in “Johnson” and “ston” in “Johnston.”
.Any single character except newline .an matches “ran” and “can.”
x|yEither x or y FF0000|000FF matches "FF0000" in BGCOLOR="#FF0000" and "0000FF" in FONT COLOR="#0000FF."
{n}Exactly n occurrences of the preceding character o{2} matches “oo” in “loom” and the first two o's in “mooooo.”
{n,m}At least n and at most m occurrences of the preceding character F{2,4} matches "FF" in "#FF0000" and the first four Fs in "#FFFFFF."
[abc]Any one of the characters enclosed in the brackets [aeiou] initially matches “a” in “apple,” “e” in “egg,” and “i” in “pig.” Specify a range of characters with a hyphen (for example, [a-f] is equivalent to [abcdef]).
[^abc]Any character not enclosed in the brackets [^aeiou] initially matches “r” in “orange,” “b” in “book,” and “k” in “eek!”. Specify a range of characters with a hyphen (for example, [^a-f] is equivalent to [^abcdef]).
\bA word boundary (such as a space or carriage return) \bb matches “b” in “book” but nothing in “goober” or “snob.”
\BA nonword boundary \Bb matches “b” in “goober” but nothing in “book.”
\dAny digit character. Equivalent to [0-9]\d matches “3” in “C3PO” and “2” in “apartment 2G.”
\DAny nondigit character. Equivalent to [^0-9]\D matches “S” in “900S” and “Q” in “Q45.”
\fForm feed  
\nLine feed  
\rCarriage return  
\sAny single whitespace character, including space, tab, form feed, or line feed \sbook matches “book” in “blue book.”
\SAny single non-whitespace character \Sbook matches “book” in “notebook” but nothing in “blue book.”
\tA tab  
\wAny alphanumeric character, including underscore. Equivalent to [A-Za-z0-9_]b\w* matches “barking” in “the barking dog” and both “big” and “black” in “the big black dog.”
\WAny nonalphanumeric character. Equivalent to [^A-Za-z0-9_]\W matches “&” in “Jake & Mattie” and “%” in “100%.”



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