Keyword Forensics

Abstract

The objectives of this chapter are to:

Appendix: Regular Expression Metacharacters [2, 4]

Metacharacter	Description
^	Matches the following item at the beginning of a text line
$	Matches the preceding item at the end of a text line
.	Matches any single character
[…]	A bracket expression. Matches a single character in the bracketed list or range
[^…]	Matches a single character that is not contained within the brackets
( )	Defines a marked subexpression. A marked subexpression is also called a block or capturing group. BRE mode requires
*	Matches the preceding item zero or more time
{m}	The preceding item is matched exactly m times. BRE mode requires \{m\}
{m,}	The preceding item is matched N or more times. BRE mode requires \{m,\}
{m,n}	Matches the preceding item at least m and not more than n times. BRE mode requires \{m,n\}
\	The escape of special meaning of next character

The next three metacharacters are only for extended regular expression

Metacharacter	Description
?	Matches the preceding character, metacharacter, or expression zero or one time
+	Matches the preceding character, metacharacter, or expression one or more times. There is no limit to the amount of times it can be matched
|	Matches the character, metacharacter, or expression on either side of it

Note that to use the grep command to search for metacharacters, you have to use a backslash (\) to escape the metacharacter. For example, the regular expression “^\.” matches lines that start with a period.