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Regular expressions (REs), unlike simple queries, allow you to search for text which matches a particular pattern.
REs are similar to (but more poweful than) the "wildcards" used in the command-line interfaces found in operating systems such as Unix and MS-DOS. REs are used by sophisticated search engines, as well as by many Unix-based languages and tools ( e.g., awk, grep, lex, perl, and sed ).
Examples
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compan(y|ies)
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Search for company , companies
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(peter|paul)
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Search for peter , paul
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bug*
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Search for bug , bugs , bugfix
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[Bb]ag
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Search for Bag , bag
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b[aiueo]g
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Second letter is a vowel. Matches bag , bug , big
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b.g
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Second letter is any letter. Matches also b&g
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[a-zA-Z]
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Matches any one letter (not a number and a symbol)
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[^0-9a-zA-Z]
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Matches any symbol (not a number or a letter)
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[A-Z][A-Z]*
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Matches one or more uppercase letters
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[0-9][0-9][0-9]-[0-9][0-9]-
[0-9][0-9][0-9][0-9]
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US social security number, e.g. 123-45-6789
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