Shell Simple Usage Notes

One, the main use of the Bash Shell in Linux; View the supported shell types available on Linux systems :

Vim/etc/shell

The way to perform shel footsteps:

1. Give footsteps the ability to execute permissions and invoke the script using a relative or absolute path

chmod  755  Test. SH    #赋予该脚本可执行权限. /test. SH                      #以相对路径执行该命令~/test. SH                   #一绝对路径执行该命令

2. Invoke the script with the shell command (the script may not need to execute permissions at this time):

bash  test.js     #使用bash Shell executes sh      test.js     #使用sh执行

Note: The shell script is #! /bin/bash begins by saying that the shell script is written (equivalent to PHP's <?php?>)

Second, the Shell History Command view

Run: History to see the commands that have been used under the user (through the up and down arrows to see the previous or next command executed)

Use Vim ~/.bash_history to view historical commands that have been maintained

You can view the maximum number of saved history entries by viewing the/etc/profile

By:!n the nth command of the repeatable history record

By:!str can repeat the last history command starting with Str

C. Shell definition aliases

The  aliasls"ls-l"   #定义ls-L is named LS, and is actually executed when LS is executed ls-l

Configuration of aliases (configuration aliases are permanently active):

Edit ~/.BASHRC

Iv. output Redirection

Standard output/dev/stdin 0 keyboard

Standard output/dev/stdout 1 display

Standard error Output/dev/strerr 2 display

ls > AA cover to AA

LS >> AA append to AA

LS hahah 2>aa output error to AA (no spaces on both sides of the error output)

LS &> AA will output correct and error to AA

V. Execution of multiple orders

ls Date           #中断中输入后会顺序执行该3条命令  ls  Date       #前一条正确执行后, execute LS AAA on the following line   | |  Date        #前一条命令错误执行, the next command executes the lsechoecho no          #ls  AAA correctly executes output Yes, executes error output nolsgrep  etc    #前一条命令的执行结果 as the execution condition of the latter command

Vi. variables

1. Variable classification

• Local variables
• Environment variables
• Positional parameter variables
• Pre-defined variables

Environment variable configuration file:

/etc/profile

/etc/bashrc

~/.bashrc

~/.bash_profile

The first two take effect for all users, and the latter two for the specified user

Shell Simple Usage Notes