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Regular expressions are used to describe patterns in text. The following characters are regular expression operators (or metacharacters) used by the Find and Delete Options dialog to increase the power and versatility of regular expressions.
Caret matches the beginning of the string or the beginning of a line within the string. For example:^@chapter matches the “@chapter” at the beginning of a string.
—|—
$
Dollar sign is similar to the caret, but it matches only at the end of a string or the end of a line within the string. For example:p$ matches a record that ends with a p.
.
Period (.) matches any single character except a new line. For example: .P matches any single character followed by a P in a string. Using concatenation we can make regular expressions like ‘U.A’, which matches any three-character sequence that begins with ‘U’ and ends with ‘A’.
[…]
This is called a character set. It matches any one of the characters that are enclosed in the square brackets. For example: [MVX] matches any one of the characters M, V, or X in a string. Ranges of characters are indicated by using a hyphen between the beginning and ending characters, and enclosing the whole thing in brackets. For example:[0-9] matches any digit. To match ‘-‘, write it as ‘—’, which is a range containing only ‘-‘. You may also give ‘-‘ as the first or last character in the set. To match ‘^’, put it anywhere except as the first character of a set. To match a ‘]’, make it the first character in the set. For example: []d^]matches either ‘]’, ‘d’ or ‘^’.
[^ …]
This is a complemented character set. The first character after the [ must be a ^. It matches any characters except those in the square brackets (or newline). For example: [^0-9] matches any character that is not a digit.
Vertical bar is the alternation operator and it is used to specify alternatives. For example: ^P|[0-9]matches any string that matches either ^P or [0-9]. This means it matches any string that contains a digit or starts with P. The alternation applies to the largest possible regexps on either side. No spaces are allowed between strings and the alternation operator.
{…}
Brackets are used for grouping in regular expressions as in arithmetic. They can be used to concatenate regular expressions containing the alternation operator, |.
*
Asterisk means that the preceding regular expression is to be repeated as many times as possible to find a match. For example: ph* applies the * symbol to the preceding h and looks for matches to one p followed by any number of h’s. This will also match just p if no h’s are present. The * repeats the smallest possible preceding expression (use parentheses if you wish to repeat a larger expression). It finds as many repetitions as possible. For example: (c[ad][ad]*r x) matches a string of the form (car x), (cdr x), (cadr x), and so on.
+
Plus sign is similar to , but the preceding expression must be matched at least once. This means that: wh+y would match “why” and “whhy” but not “wy,” whereas why would match all three of these strings. This is a simpler way of writing the last * example: (c[ad]+r x)
?
Question mark is similar to *, but the preceding expression can be matched once or not at all. For example: fe?d will match fed and fd, but nothing else.
\
Backslash is used to suppress the special meaning of a character when matching. For example: $ matches the character $.
In regular expressions, the *, +, and ? operators have the highest precedence, followed by concatenation, and finally by |.