Multi-command sequential execution, single quote, double quote, anti-quote, escape character

Sequential execution of MULTIPLE commands
; sequential execution of multiple commands
&& logic with previous command execution OK, followed by
|| logical OR previous command execution failed after execution
| Command 1| Command 2 command 1 result, let the command handle
Wildcard characters
？ match any one character
* match 0 or more of any characters
[] matches any one of the characters in brackets
[-] match any one of the characters in parentheses
[^] logical non-match is not one of the characters in brackets

[email protected] biji]# aa=666
[[email protected] biji]# echo $AA # print variable AA
666
[[email protected] biji]# echo ' $aa ' #单引号, print characters $aa
$aa
[email protected] biji]# echo "$aa" #打印变量aa
666
[[email protected] biji]# bb= ' ls ' #反引号, variable ls value, assigned to BB
[email protected] biji]# echo $BB
1.txt axel-2.4-1.el5.rf.x86_64.rpm Sogou_pinyin_wubi_2.0.1.1221.1432288488.exe
[[email protected] biji]# bb=$ (du) assign a value to BB #du variable
[email protected] biji]# echo $BB
9092.
[[email protected] biji]# echo \ $bb # \ Represents escape character
$BB

Multi-command sequential execution, single quote, double quote, anti-quote, escape character