Special characters of the shell

Bash is a powerful scripting language, which is the default shell in many Linux occurrences, supports variables and special characters, and looks at what special characters it has:

; Command delimiter, you can write multiple commands in one line

;; Terminate case option

. Shell built-in command, equivalent to source,

. As part of the file name, if it is a prefix, it is represented as a hidden file

. Character matching, which represents a single character in a regular expression

"Double quotes, weak references, can implement variables

' Single quotes, strong references, reference characters themselves

\ escape Character

' Post reference, command replace '

: Empty command, just do nothing, in script: > A.txt equals cat/dev/null > A.txt

！ Take the inverse operator, the shell keyword

* Any word matching, in arithmetic operation * * is a power operation

${} reference variable

$? Exit state variable

$# the number of parameters in a bash script

$* [email protected] A list of parameters represented in a bash script

$ A script name

() command group: For example: (A=3;echo $a), note the variable in () whose use is limited to () and produces a child shell run

{A, B} curly brace extension, such as cat {A.txt,dns.sls} > C.txt

An expression of [] test that represents the range of character matching in a regular expression

(()) Extension of data calculation

> Standard output redirection

2> Error Output redirection

&> Redirect all outputs

< output redirection

|| Or, the logical operation

&& and, logical operations

{} code block, this structure creates an anonymous function, but unlike a function, the declared variable is visible to the rest of the script.

Such as:

#!/bin/bash

A=5

{a=123;}

Echo $a #a =123 describes the modification of variable A in the code block, which affects the outer variable a

-For redirecting stdin or stdout, such as: Ls/root | Cat-or grep ' C ' a.txt | Diff C.txt-

^ indicates positioning to the beginning of the line

This article from "10,000 years too long, seize" blog, please be sure to keep this source http://zengwj1949.blog.51cto.com/10747365/1916402

Special characters of the shell