Shell (11) shell .doc

Basic Concepts

X
Window

Interoperate with display & video card

Xfree86
And x.org

The Open Source version of X Window

KDE/gnome,

 

Character Set

A set of binary commands,
Linux
The system sends a message to the monitor to display characters.

ASCII

ISO-8859-x, Unicode (all iso-8xx encoded)

 

Analog Terminal

Simulate old-fashioned
UNIX
Non-intelligent terminal, defining terminal parameters such as display cache, graphics vector, number of characters in a row, and defining buttons

 

Environment Variable
Term

Define the simulated terminal used

 

Xterm

Terminal simulator package

 

Topic: script format

Variable assignment"
=
"No space on both sides

If
Conditional judgment
[]
Must contain spaces,
If
Space is also required between and [

Variable reference, except the value assignment and
For
All external applications
$

Double quotation marks allow replacement of variables and commands

Single quotes avoid special wildcard characters being interpreted, such
$? | <>
,
Eg: Echo '$ abc' # $ ABC
Not interpreted as a variable
ABC

Another variable reference method:

$ {Variable}

Bash
Escape Character,
/

 

Environment
Values

Printenv, show all EVN values

Global env values:
Uppercase: Any process with Defined variables and its sub-processes are visible;

Local env values:
Lowercase, only visible in the local process that defines it, such as the current
Shell
;

Set, show all env values, global &
Local encoded ded.

Set env values, use "" or '':
A = "a B C"

Export,
Set local
Env
Export to global
Env
;

Delete env: unset xxx

 

Some default environment variables:

Path

Home

Tmout

, Set how long after idle
Bash
Automatically exit

Display

 

Mathematical operations

Expr 5/* 2
#
Space Required

Var = $ [5*2]
#
No space,
Bash
Private

Var = $ [$ Var * (2 + $ var)]

You can also:

Var = $(5*2 ))

 

Script exit

Exit status:
$?
Maximum Value
255

Exit command
: Exit 0
#
Can I use it like a function?
Return
?
TBD

 

Bash
Variable Array

Define
:
A = (1 2 3 4)
, Separated by spaces,
()

Echo $ {A [1]}
# Use:
Index Based on
0

Echo $ {A [*]}
# Show All members

A [1] = 20


# Set a member

Unset


# Deleted

TBD
:
How to add members to the array?

 

Bash
Three startup Methods

1
Default Logon Time
Shell
, Run
/Etc/profile
,
$ Home/. bash_profile,
$ Home/. bash_login, $ home/. Profile

2
, Non-Logon interactive
Shell
, Processing
~ /. Bashrc

3
, Non-interactive running scripts
Shell
,
$ Bash_env
Start script to be executed

 

/Etc/profile

Run the command at the First Login and
/Etc/profile. d
Under the configuration file to collect
Shell
Settings

~ /. Bash_profile

When the user logs on
~ /. Bashrc

~ /. Bashrc

Set
Alias
And call
/Etc/bashrc

/Etc/bashrc


Each execution
/
Open
Bash
The content can be
~ /. Bashrc
Overwrite

~ /. Bash_logout

 

/Etc/profile,
Read
/Etc/profile. d
The configuration file in the directory, which is executed during the First Login

~ /. Profile

~ /. Bash_login

~ /. Bash_profile

~ /. Bashrc
, The best place to add environment variables and aliases

~ /. Bash_logout
,
Logout
Time execution

 

Others

Coreutils package, the core utilities
Linux from GNU

Echo-n xxx,
No line feed output

 

User Manage

UID
Less
100
Users created with various non-real-user functions

/Etc/passwd

User_name: Pwd: uid: GID: Comments: home_dir: deault_shell

/Etc/shadom

Useradd-D # Show default setting for adding
User. skel set a pattern for the home Dir of the new user.

Userdel, del
User, param-R is appended if u want to Del
The home_dir also

Usermod, Set User such as adding user to
Group

Passwd, Change Password

Finger root, show User Info

 

Group

/Etc/group

Name: Pwd: GID: user_list

Passwd of group:
Used to temporarily become a member of this group

Null user_list:/etc/passwd
The default group users in
Group
In the user list

Usermod-G group1 user1
: Add user to a group

Groupadd

Groupmod

ID
Command to display all groups of users

 

File Permission

Umask, set the default value of the new
Created file.

Chmod 760 newfile

Chmod + x newfile
# +,-, =

Chown chgrp

 

 

File Attributes

Set User ID (SUID)
, The file will be executed under the file owner permission, not the file executor permission, such
Root
All, then the common user will also
Root
Permission to execute this program

Set Group ID (SGID)
For a directory, the user group of the directory will be used as the default user group for creating new files in the directory; a method for creating shared folders for multiple users;

Stick bit: After the process ends, the file is still in the memory (?)

Chmod + S xxx
, Set
SGID
Bit

 

Temporary Files

Mktemp ABC. xxxxxx
#6
Items
X
Will be randomly generated,
X
The quantity must be greater
3
, Command to return the generated file name (default current directory ),
Xx
It must be at the end of the name

Mktemp-t abc. xxx
#
In
/Tmp
File generation

Mktemp-d abc. xxx
#
Create temporary directory

 

String processing

Use
### %
String Truncation

Use
Expr
Obtain the string length, substring, and so on,

Expr substr string POS Length

Eg:

Expr
Substr ABCD 1 100
# POS

Slave
1

Start,
Length

It can be larger than the actual length

Expr Length
ABCD