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
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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:
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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$
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Linux wildcard characters, metacharacters, and special characters