Wildcard

In data transmission, a joker symbol is a symbol with which you can replace any predefined set of other symbols.

• In the high-frequency radio range (HF) during automatic communication ( English automatic link establishment ), the character “?” Can correspond to any of the following 36 characters: from “ A ” to “ Z ” and from “ 0 ” to " 9 ".
• It must be agreed in advance whether the joker represents a single character or a string of characters .

Most often, two different characters are used - to replace any string of characters and to replace any single character. The asterisk ( * ) is almost always used as the first. At the same time, it can also mean an empty string (absence of characters).

In command line interpreters of various operating systems: COMMAND.COM in DOS , cmd.exe in Microsoft Windows , various script shells in * nix - wildcard characters are used: a question mark ( ? ) As a replacement for one character and an asterisk in the above sense. Using them, you can operate (list, delete, copy, etc.) immediately with groups of files. Examples of commands:

  copy * .txt> all.txt    

copies the contents of all text files in the current directory to a single file (DOS, Windows).

  rm *. ???

deletes all files in the current directory whose extension consists of exactly three characters ( sh ).

In database management programs, such as SQL (instead of *, the percent sign is %, instead of? Is the underscore _) or Microsoft Access , more precisely in their scripting languages, wildcard characters can be used in LIKE expressions:

SELECT * FROM books WHERE book_name LIKE '%хими%';

In regular expressions, the concept of wild symbols has been further developed. They have special notation not only for one (".") And any number (quantifier "*") of characters, but also for different classes of characters (for example, empty characters "\ s"), alternative expressions ("|") and much more another.

• MIL-STD-188

• Search pattern

• How to Use Wildcards
• shwild: Shell-compatible wildcards (C / C ++ )