Linux wildcard characters, metacharacters, and special characters

Features that are useful in bash environments: wildcards, escape characters, and special characters are described below

One, wildcard characters

A wildcard is a special statement that has an asterisk (*), a question mark (?). And so on, used to blur the search file, when looking for a directory or file, you can use wildcard characters instead of one or more true positive characters.

Scope: directory and file name

Common wildcard characters: Common wildcard characters include "*", "?", "[]", "[^]", "[!]" and "{}", the specific meaning is shown in the following table

Table 1-1 the specific meanings and usage tables of the wildcard characters

Character	Meaning
*	Horse character with any word
？	Match a single character
[]	Matches any one of the square brackets and cannot be used to create directories and files
[^]	Match any one of the characters or numbers in the square brackets and reverse them, equivalent to [! ], indicating that the range can be used with ".." or "-" to find and delete directories and files without creating directories and files
[!]	Match any one of the characters or numbers in the square brackets after the inverse, equivalent to [^], indicating that the range can be used "..." or "-" to find and delete directories and files without creating directories and files
[？ -？ ]	Matches any one of the brackets in the range, for querying, deleting, but not for creating directories and files
{string,string}	Matches any one of the strings in parentheses, representing a range, between strings "..."

specific usage one by one illustration

• Root creates directories F1 and F2 at once, and now requires a one-time removal of F1 and F2 files via wildcard characters
  

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• Root created F1 to F9, now requires a one-time wildcard creation and removes F5 to F8

Error usage 1: Use square brackets to create a F1 to F9 directory,

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Error usage 2: Use curly braces-to represent a range to create a directory F1 to F9

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to create a directory correct practice: The correct approach is to use braces, scope with ".." Represents

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Delete directory One of the correct methods: use [^] or [!] to Undelete

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Two, meta characters

Metacharacters: The shell is responsible for interpreting the processing, and special characters have special meanings.

Character	Meaning
=	Set variables, function assignments, etc.
$	Replace as a variable or operation
> or "	REDIRECT StdOut
< or the	REDIRECT StdIn
&	The 2>1& translates the standard error output to the standard correct output, 1>2$ the standard positive output to the standard error output &> positive fetch error Output
( )	Combining $ () with "$ ()" To implement command invocation, the parentheses in the synthetic operation are preferred
{}	Scope defined, such as for I in {1..10}, variable I value range 1 to 10
;	Semicolon, multiple commands are executed in turn, the execution process is not dependent
&&	Previous command execution feedback is correct, that is $?=0, continue to execute next command
||	The previous command performs a feedback error, that is, $?=1, and then proceeds to the next command
！ and ~	！ Reference history statement, ~ is home directory

To illustrate:

• View/app/hellohh and/app directory files with LS and redirect to 1.log file for problem analysis

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redirect both correct and incorrect standard output through &>

Three, escape character

escape character: The character meaning of the wildcard character and the metacharacters into itself

Character	Meaning
‘ ’	Hard escaping, comparing silly character references, preserving the original character meaning, not escaping
" "	Soft escaping, escaping special characters into characters with special meanings
$ () equivalent to '	Force Reference Command,
\	Display the original special character

specific examples are as follows:

• Define alias Baketc, daily manual Regular backup of all files in/etc directory, backup to/testdir Independent subdirectory, and require subdirectory format BAKUPYYYY-MM-DD, backup process visible (strong reference ")

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• Add user bash, Testbash, basher, SH, nologin (shell is/sbin/nologin), find the/etc/passwd file, the user name and the shell name of the row

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WHERE. * The first \ is the escape character, which represents the string ending with/string$

• After configuring the NIC information, the IP configuration error is found, so the NIC information is reconfigured using the history command.

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Linux wildcard characters, metacharacters, and special characters