In
computer (
software) technology, a wildcard is a symbol used to replace or represent zero or more characters.
Algorithms for matching wildcards have been developed in a number of
recursive and non-recursive varieties.
File and directory patterns When specifying file names (or paths) in
CP/M,
Atari DOS,
MS-DOS,
Windows, and
Unix-like operating systems, the
asterisk character (, also called "star") matches zero or more characters. For example, matches and but not . If files are named with a date stamp, wildcards can be used to match date ranges, such as *.mp4 to select video recordings from , to facilitate file operations such as copying and moving. In Unix-like operating systems, MS-DOS, and Atari DOS, the
question mark matches exactly one character. In MS-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 will match and , but not . In
Unix shells and
Windows PowerShell, ranges of characters enclosed in
square brackets ( and ) match a single character within the set; for example, 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 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 In
regular expressions, the
period (, also called "dot") is the wildcard pattern which matches any single character. Followed by the
Kleene star operator, which is denoted as an
asterisk (), we obtain , which will match zero or more arbitrary characters.
Search engines The wildcard operator can be used in
Google Search to fetch results which have one or more word(s) inserted between phrases; e.g. Googling "I love * so much" will populate results such as "I love this game so much," "I love my wife so much," etc.
Namespaces In some languages, such as
Java and
Rust, an asterisk can be used to qualify all symbols inside a namespace (sometimes called a "glob import" or "wildcard import"). For example, in Java import java.util.*; adds into scope all public classes from the java.util package, while in Rust use std::collections::*; adds into scope all public symbols from the std::collections module. ==See also==