The term wildcard character has the following meanings:
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In telecommunications, a wildcard character is a character that may be substituted for any of a defined subset of all possible characters.
In computer (software) technology, a wildcard character can be used to substitute for any other character or characters in a string.
When specifying file names (or paths) in CP/M, DOS, Microsoft Windows and Unix-like operating systems, the asterisk character ("*") substitutes for any zero or more characters, and the question mark ("?") substitutes for any one character or less but not more than the amount of question marks. For example 123??? will match 1231 or 12313 but not 1239919991. In Unix shells and Windows PowerShell, ranges of characters enclosed in square brackets ("[" and "]") substitute for all the characters in their ranges; for example, [A-Za-z] substitutes for any single capitalized or lowercase letter. Unix shells allow negation of the specified characters within brackets by using a leading "!". Matching wildcard patterns to multiple files or paths is referred to as glob expansion.
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 ^ matches only a character not specified within the brackets. In Microsoft Access, wildcard characters can be used in "LIKE" expressions; the asterisk sign (*) matches zero or more characters, and question mark (?) a single character.
In SAP the plus-sign (+) matches exactly one character.
In regular expressions, the period (.) is the wildcard character for a single character. Combined with the asterisk operator (.*) it will match any number of characters.