Wildcard character
 | This article relies largely or entirely on a single source. (May 2016) |
In software, a wildcard character is a kind of placeholder represented by a single character, such as an asterisk (*), which can be interpreted as a number of literal characters or an empty string. It is often used in file searches so the full name need not be typed.[1]
Telecommunication[edit]
In telecommunications, a wildcard is a character that may be substituted for any of a defined subset of all possible characters.
- In high-frequency (HF) radio automatic link establishment, the wildcard character
?may be substituted for any one of the 36 upper-case alphanumeric characters. - Whether the wildcard character represents a single character or a string of characters must be specified.
Computing[edit]
In computer (software) technology, a wildcard is a symbol used to replace or represent one or more characters.[2] Algorithms for matching wildcards have been developed in a number of recursive and non-recursive varieties.[3]
File and directory patterns[edit]
When specifying file names (or paths) in CP/M, DOS, Microsoft Windows, and Unix-like operating systems, the asterisk character (*, also called "star") matches zero or more characters. For example, doc* matches doc and document but not dodo.
In Unix-like and DOS operating systems, the question mark ? matches exactly one character. In DOS, if the question mark is placed at the end of the word, it will also match missing (zero) trailing characters; for example, the pattern 123? will match 123 and 1234, but not 12345.
In Unix shells and Windows PowerShell, ranges of characters enclosed in square brackets ([ and ]) match a single character within the set; for example, [A-Za-z] matches any single uppercase or lowercase letter. In Unix shells, a leading exclamation mark ! negates the set and matches only a character not within the list. In shells that interpret ! as a history substitution, a leading caret ^ can be used instead.
The operation of matching of wildcard patterns to multiple file or path names is referred to as globbing.
Databases[edit]
In SQL, wildcard characters can be used in LIKE expressions; the percent sign % matches zero or more characters, and underscore _ a single character. Transact-SQL also supports square brackets ([ and ]) to list sets and ranges of characters to match, a leading caret ^ negates the set and matches only a character not within the list. In Microsoft Access, the asterisk sign * matches zero or more characters, the question mark ? matches a single character, the number sign # matches a single digit (0-9), and square brackets can be used for sets or ranges of characters to match.
Regular expressions[edit]
In regular expressions, the period (., also called "dot") is the wildcard pattern which matches any single character. Combined with the asterisk operator .* it will match any number of any characters.
In this case, the asterisk is also known as the Kleene star.
See also[edit]
References[edit]
- ^ "Microsoft Corporation". www.microsoft.com. Archived from the original on 2017-03-24. Retrieved 2018-01-23.
- ^ "What is wildcard?". Archived from the original on 2016-11-21. Retrieved 2016-11-21.
- ^ Cantatore, Alessandro (2003). "Wildcard matching algorithms".
This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C". (in support of MIL-STD-188)
This article incorporates