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Regular expressions and syntax
A regular expression is a pattern that describes a set of strings. A regular expression is a sequence of any of the following items:
literal character
matching character
repetition clause
alternation clause
subpattern grouped with parenthesis
Regular expressions syntax
The following table lists the regular expression syntax with its corresponding descriptions:
Syntax
Description
.
Matches any character; used as a wildcard when creating a search string.
*
Matches zero or more instances of the previous pattern item.
+
Matches one or more instances of the previous pattern item.
?
Matches zero or one instance of the previous pattern item.
( )
Groupssubpattern; repetition and alternation operators apply to the entire preceding subpattern.
|
Allows for an alternation of a pattern.
For example, to match Hello or hello in a string, the regular expression should read: Hello|hello.
[ ]
Delimits a set of characters; the range is specified as [x-y].
If the first character in the set is ^, there is a match only when the remaining characters in the set are not present.
^
Anchors the pattern to the beginning of the string; this character must be the first character in the set.
$
Anchors the pattern to the end of the string; this character must be the last character in the set.
Provides regular expression syntax with its corresponding descriptions.
