Wildcards linux что это

How to Use Wildcards

A wildcard is a character that can be used as a substitute for any of a class of characters in a search, thereby greatly increasing the flexibility and efficiency of searches.

Wildcards are commonly used in shell commands in Linux and other Unix-like operating systems. A shell is a program that provides a text-only user interface and whose main function is to execute commands typed in by users and display their results.

Wildcards are also used in regular expressions and programming languages. Regular expressions are a pattern matching system that uses strings (i.e., sequences of characters) constructed according to pre-defined syntax rules to find desired strings in text.

The term wildcard or wild card was originally used in card games to describe a card that can be assigned any value that its holder desires. However, its usage has spread so that it is now used to describe an unknown or unpredictable factor in a variety of fields.

Star Wildcard

Three types of wildcards are used with Linux commands. The most frequently employed and usually the most useful is the star wildcard, which is the same as an asterisk (*). The star wildcard has the broadest meaning of any of the wildcards, as it can represent zero characters, all single characters or any string.

As an example, the file command provides information about any filesystem object (i.e., file, directory or link) that is provided to it as an argument (i.e., input). Because the star wildcard represents every string, it can be used as the argument for file to return information about every object in the specified directory. Thus, the following would display information about every object in the current directory (i.e., the directory in which the user is currently working):

If there are no matches, an error message is returned, such as *: can’t stat `*’ (No such file or directory).. In the case of this example, the only way that there would be no matches is if the directory were empty.

Wildcards can be combined with other characters to represent parts of strings. For example, to represent any filesystem object that has a .jpg filename extension, *.jpg would be used. Likewise, a* would represent all objects that begin with a lower case (i.e., small) letter a.

As another example, the following would tell the ls command (which is used to list files) to provide the names of all files in the current directory that have an .html or a .txt extension:

Likewise, the following would tell the rm command (which is used to remove files and directories) to delete all files in the current directory that have the string xxx in their name:

Question Mark Wildcard

The question mark (?) is used as a wildcard character in shell commands to represent exactly one character, which can be any single character. Thus, two question marks in succession would represent any two characters in succession, and three question marks in succession would represent any string consisting of three characters.

Thus, for example, the following would return data on all objects in the current directory whose names, inclusive of any extensions, are exactly three characters in length:

And the following would provide data on all objects whose names are one, two or three characters in length:

As is the case with the star wildcard, the question mark wildcard can be used in combination with other characters. For example, the following would provide information about all objects in the current directory that begin with the letter a and are five characters in length:

The question mark wildcard can also be used in combination with other wildcards when separated by some other character. For example, the following would return a list of all files in the current directory that have a three-character filename extension:

Square Brackets Wildcard

The third type of wildcard in shell commands is a pair of square brackets, which can represent any of the characters enclosed in the brackets. Thus, for example, the following would provide information about all objects in the current directory that have an x, y and/or z in them:

And the following would list all files that had an extension that begins with x, y or z:

The same results can be achieved by merely using the star and question mark wildcards. However, it is clearly more efficient to use the bracket wildcard.

When a hyphen is used between two characters in the square brackets wildcard, it indicates a range inclusive of those two characters. For example, the following would provide information about all of the objects in the current directory that begin with any letter from a through f:

And the following would provide information about every object in the current directory whose name includes at least one numeral:

The use of the square brackets to indicate a range can be combined with its use to indicate a list. Thus, for example, the following would provide information about all filesystem objects whose names begin with any letter from a through c or begin with s or t:

Likewise, multiple sets of ranges can be specified. Thus, for instance, the following would return information about all objects whose names begin with the first three or the final three lower case letters of the alphabet:

Sometimes it can be useful to have a succession of square bracket wildcards. For example, the following would display all filenames in the current directory that consist of jones followed by a three-digit number:

Created July 17, 2006.
Copyright © 2006 The Linux Information Project. All Rights Reserved.

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Русские Блоги

Команда Linux — Wildcard, Bash Environment Специальные символы, регулярные выражения

В команде Linux есть разница между подстановочными знаками и регулярными выражениями.

Подстановочный знак

Подстановочные знаки используются для имени файлов, которые полностью совпадают, что анализируется оболочкой, такими как Find, LS, CP, MV и т. Д., Такая как Find, Ls, CP и MV, не может использовать регулярные выражения, только собственную оболочку Подстановочные знаки могут быть сопоставлены, обычный подстановочный знак:

Использовать * и? Первое вхождение оболочки — это начало оболочки. Bash сканирует каждое слово в командной строке, если вы найдете * или [, то это слово считается режимом. Затем этот режим заменяется списком имени файлов, которые соответствуют алфавитным порядке. Быть простым, Bash будет соответствовать и заменить его до выполнения команды LS. Тогда Ls использует параметр замены для выполнения команды, такой как выполнение

Если есть каталог, называемый тестом и каталог, называемый TestSQL, то замена Bash подобна этому:

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#Примечание символ

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10 Practical Examples Using Wildcards to Match Filenames in Linux

Wildcards (also referred to as meta characters) are symbols or special characters that represent other characters. You can use them with any command such as ls command or rm command to list or remove files matching a given criteria, receptively.

These wildcards are interpreted by the shell and the results are returned to the command you run. There are three main wildcards in Linux:

• An asterisk (*) – matches one or more occurrences of any character, including no character.
• Question mark (?) – represents or matches a single occurrence of any character.
• Bracketed characters ([ ]) – matches any occurrence of character enclosed in the square brackets. It is possible to use different types of characters (alphanumeric characters): numbers, letters, other special characters etc.

You need to carefully choose which wildcard to use to match correct filenames: it is also possible to combine all of them in one operation as explained in the examples below.

How to Match Filenames Using Wildcards in Linux

For the purpose of this article, we will use following files to demonstrate each example.

1. This command matches all files with names starting with l (which is the prefix) and ending with one or more occurrences of any character.

List Files with Character

2. This example shows another use of * to copy all filenames prefixed with users-0 and ending with one or more occurrences of any character.

List and Copy All Files

3. The following command matches all files with names beginning with l followed by any single character and ending with st.sh (which is the suffix).

Match File with Character Name

4. The command below matches all files with names starting with l followed by any of the characters in the square bracket but ending with st.sh .

Matching Files with Names

How to Combine Wildcards to Match Filenames in Linux

You can combine wildcards to build a complex filename matching criteria as described in the following examples.

5. This command will match all filenames prefixed with any two characters followed by st but ending with one or more occurrence of any character.

Match File Names with Prefix

6. This example matches filenames starting with any of these characters [clst] and ending with one or more occurrence of any character.

Match Files with Characters

7. In this examples, only filenames starting with any of these characters [clst] followed by one of these [io] and then any single character, followed by a t and lastly, one or more occurrence of any character will be listed.

List Files with Multiple Characters

8. Here, filenames prefixed with one or more occurrence of any character, followed by the letters tar and ending with one or more occurrence of any character will be removed.

Remove Files with Character Letters

How to Match Characters Set in Linux

9. Now lets look at how to specify a set of characters. Consider the filenames below containing system users information.

This command will match all files whose name starts with users-i , followed by a number, a lower case letter or number, then a number and ends with one or more occurrences of any character.

The next command matches filenames beginning with users-i , followed by a number, a lower or upper case letter or number, then a number and ends with one or more occurrences of any character.

This command that follows will match all filenames beginning with users-i , followed by a number, a lower or upper case letter or number, then a lower or upper case letter and ends with one or more occurrences of any character.

Match Characters in Filenames

How to Negate a Set of Characters in Linux

10. You can as well negate a set of characters using the ! symbol. The following command lists all filenames starting with users-i , followed by a number, any valid file naming character apart from a number, then a lower or upper case letter and ends with one or more occurrences of any character.

That’s all for now! If you have tried out the above examples, you should now have a good understanding of how wildcards work to match filenames in Linux.

You might also like to read these following articles that shows examples of using wildcards in Linux:

If you have any thing to share or a question(s) to ask, use the comment form below.

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