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 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
[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
. If files are named with a date stamp, wildcards can be used to match date ranges, such as 202410*.mp4
to select video recordings from October 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
[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]- ^ "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).