Shulou(Shulou.com)06/03 Report--

Shen Chao:

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A brief introduction to shell

1 concept

Command interpreter

2 Common shell

Bash linux standard shell

Attachment: she is saved in / etc/bash, which is a binary executable file, so it cannot be directly:

Vim/bin/bash will be garbled.

Sh early shell, relatively simple

Csh (the default Shell for UNIX! ) ksh tcsh unix shell

PS: most of them are the same, but there will be some differences, such as where the configuration files are saved

Shell supported by vi / etc/shells linux

Typing csh directly does not report an error, because he has switched from bash to csh

(return exit)

3 shell script

Attached: create folder / file directory: mkdirsh

Unlike Windows, Linxu does not distinguish between extensions!

#! / bin/bash

Example 1: print time

#! / bin/bash

Echo "hello world!"

How the script is executed:

1) Grant execution authority (idiom)

Such as: chmod755 hello.sh

Path execution / root/shell/hello.sh# absolute path

. / hello.sh # relative path

2) No executive permission is granted

Bash script name

Such as: bashecho.sh

4 Common features of bash

1) Historical commands

1000 history commands are saved by default:

Vi / etc/profile modifies the environment variable configuration file. To take effect, you must log out.

HISTSIZE=1000 modifies the default number of historical commands

History query system history command

History command save file

~ / .bash_history

History-w saves the history of commands in memory into a file

History-c clears all historical commands

Repeat the history command

! N repeat the command under article n

! Str repeats the last command that starts with str

The up arrow calls the above command

2) Alias

Attachment: Linux will display folders in blue after using ls by default

But you can also use: ls-- color=never to cancel the display color

Alias view aliases in effect in the system

Attached:

Alias ls='ls-color=never' sets aliases manually and takes effect temporarily: quite in line with personal operating habits

Aliasls='ls-color=tty' # changed back

Vi ~ / .bashrc is written to the alias, which is permanently effective # the second environment variable configuration file

5 input and output redirection

Standard input / dev/stdin 0 keyboard

Standard output / dev/stdout 1 display

Standard error output / dev/stderr 2 monitor

# device file name # file descriptor # default device

1) output redirection

Redirect the output that should be output to the screen to a file.

> overwrite

> append

Ls > aa overwrites to aa

Ls > > aa appended to aa

Ls gdlslga 2 > > aa error message output to aa emphasis: error output, no spaces

Ls & > aa errors and corrections are entered into aa

Master (check the system version: uname-r)

Ls > > aa 2 > > bb correct information enter aa, error information enter bb

Ls > > aa 2 > & 1 both errors and corrections are entered into aa and can be appended

2 > & 1 redirect standard error to standard correct output

6 sequential execution of multiple commands

1) Command 1; Command 2; Command 3 Command 123 is executed sequentially. There is no relationship between cd;ls; date # date is used to print the current system time

2) Command 1 & & Command 2 Command 1 will not be executed until Command 1 is executed correctly

3) Command 1 | | Command 2 Command 1 will only be executed if it is not executed correctly, that is, if the first command is executed correctly, then the second command will not be executed!

Test-like test:

A) ls & & echo "Yes" | | echo "No"

B) ls skdjfkdj & & echo "Yes" | | echo "No"

Lsaa & & echo "cunzai" | | echo "bu cunzai!" Execute ls aa to determine that if correct, the output "exists". If it does not exist, the output "does not exist"

7 pipe character: there is a connection between the two commands

Command 1 | the execution result of command 2, as a condition for the execution of command 2

Note: the first command must have an output

Netstat-tlun | grep 80 queries the listening port number and checks whether port 80 is enabled.

Attached:

Netstat-tlun lists how many ports are being monitored

Grep extraction commands, such as grep80 # extract lines containing 80

80 is the port of Apache

Ls-l / etc/ | more displays ls content in different screens

Ls-l / etc/ | grep vim

Attached: more displays the contents of the file on different screens

Two variables: Linux identifies all variables as program string # should be Shell, right? Idon't know!

The purpose of setting variables: like passing values in a program script.

1 classification

Local variable

Environment variable

Position parameter variable

Predefined variable

2 Local variables

1) declare variable name = variable value Note: there can be no spaces around the = sign.

Aa=123

2) call

Echo $variable name

3) View variables

Set looks at all variables, including environment and local variables

4) Delete

Unset variable name

3 variable setting rules

1) variables are connected with equal signs, and the equal sign cannot have spaces

2) the variable name consists of numbers and letters and underscores and cannot start with a number

3) there are spaces in the variable value, enclosed in quotation marks such as: aa= "helloworld" # where there can be no symbols!

4) within double quotation marks, there are special characters. Such as $

5) Special characters in single quotation marks have no meaning

6) in the value of a variable, you can use the\ escape character

7) the value of the variable can call the system command directly. `Command `$ (command)

For example, cc= `ls / dev` # `is the backquote, the one under the ESC key

Or: cc=$ (ls/dev) has the same function, recommended!

Call: echo$cc

8) variable values can add up to aa=123 aa= "$aa" 456 echo $aa-> 123456

9) Environment variables must be set to uppercase

4 environment variables:

Attached: pstree: query process tree

Generally do not declare environment variables

1) Declaration

Export variable name = variable value

Cases where the export aa # variable already exists

2) View

Set view all variables

Env or export can only view environment variables, and export can see the essence-_-

Declare declares the variable type, if not specifically declared, all variables are string type

-I declared as int

-x is declared as an environment variable

3) Delete

Unset variable name

4) Common environmental variables

Echo$PATH

/ usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

The system looks for the path of the command

PATH= "$PATH": / root/shell appends the / root/shell directory as the command lookup path after the system default path

5) Environment variable profile

/ etc/bashrc takes effect for all users

/ etc/profile

~ / .bashrc takes effect only for specified users

~ / .bash_profile

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