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
editIn 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
editIn computer (software) technology, a wildcard is a symbol used to replace or represent zero 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
editWhen 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. If files are named with a date stamp, wildcards can be used to match date ranges, such as 202412*.mp4 to select video recordings from December 2024, to facilitate file operations such as copying and moving.
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
editIn 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
editIn 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
editReferences
edit- ^ "Using wildcard characters". Microsoft. Archived from the original on 2017-03-24. Retrieved 2018-01-23.
- ^ "What is a wildcard?". Computer Hope. Archived from the original on 2016-11-21. Retrieved 2016-11-21.
- ^ Cantatore, Alessandro (Apr 25, 2003). "Wildcard matching algorithms". Archived from the original on Oct 14, 2023.
This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).
