Wildcard character
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In software, a wildcard character is a kind of placeholder represented by a single character, such as an asterisk (Template:Code), 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.<ref>Template:Cite web</ref>
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 Template:Code 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 zero or more characters.<ref>Template:Cite news</ref> Algorithms for matching wildcards have been developed in a number of recursive and non-recursive varieties.<ref>Template:Cite web</ref>
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 (Template:Code, also called "star") matches zero or more characters. For example, Template:Code matches Template:Code and Template:Code but not Template:Code. If files are named with a date stamp, wildcards can be used to match date ranges, such as {{#time:Ym}}*.mp4 to select video recordings from {{#time:F}} {{#time:Y}}, to facilitate file operations such as copying and moving.
In Unix-like and DOS operating systems, the question mark Template:Code 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 Template:Code will match Template:Code and Template:Code, but not Template:Code.
In Unix shells and Windows PowerShell, ranges of characters enclosed in square brackets (Template:Code and Template:Code) match a single character within the set; for example, Template:Code matches any single uppercase or lowercase letter. In Unix shells, a leading exclamation mark Template:Code negates the set and matches only a character not within the list. In shells that interpret Template:Code as a history substitution, a leading caret Template:Code 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 Template:Code matches zero or more characters, and underscore Template:Code a single character. Transact-SQL also supports square brackets (Template:Code and Template:Code) to list sets and ranges of characters to match, a leading caret Template:Code negates the set and matches only a character not within the list. In Microsoft Access, the asterisk sign Template:Code matches zero or more characters, the question mark Template:Code matches a single character, the number sign Template:Code 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 (Template:Code, also called "dot") is the wildcard pattern which matches any single character. Followed by the Kleene star operator, which is denoted as an asterisk (Template:Code), we obtain Template:Code, which will match zero or more arbitrary characters.
See also
[edit]References
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