Regular expression is a notation for patterns of text, as opposed to exact strings of characters. The notation uses literal characters and metacharacters. Every character which does not have special meaning in the regular-expression syntax is a literal character and matches an occurrence of that character. For example, letters and numbers are literal characters. A metacharacter is a symbol with special meaning (an operator or delimiter) in the regular-expression syntax.
.
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Wildcard: any character
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*
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Repeat: zero or more occurrences of previous character or class
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^
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Line position: beginning of line
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$
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Line position: end of line
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[class]
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Character class: any character in the set
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[^class]
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Inverse class: any character not in the set
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[x-y]
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Range: any characters within the specified range
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\x
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Escape: literal use of metacharacter x
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\<xyz
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Word position: beginning of the word
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xyz\>
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Word position: end of the word
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For example, the following regular expression .* matches any string of characters, ^a matches any string beginning with character a.
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