Shell_ 00_ First meeting shell

Shell Basics

CLI（Command Line Interface）： Command line interface

1）CLI Only accept text input , And only output text and basic graphics ;

2）Linux After system startup , Create by default in the system memory 5~6 individual CLI Terminal session running

// It can be done by Ctrl+Alt+（F2~F7） Switch ,F1 For graphical interface

Shell： Users and Linux Kernel interactive program （ be based on C Language writing ）

Shell species	explain
csh （C Shell）	Grammatical similarity C Language , Internal orders 52 individual At present, it is not used much , Has been /bin/tcsh replaced
Ksh （Korn Shell）	Grammatical similarity Bourne Shell, Internal orders 42 individual Have csh Easy to use features , be relative to bash A little restrictive
tcsh	Belong to csh Enhanced Edition , And csh Fully compatible with
sh	It belongs to shortcut Has been /bin/bash replaced
zch	Linux The largest in Shell, Internal orders 84 individual More complex to use , Rarely use this Shell
bash	CentOS By default, the system uses Shell

1）bash The path of is ：/bin/bash;

2） stay /etc/passwd The last field in each row is the user's default shell

Bash Shell

Bash（GNU Bourne-Again Shell）： A number of Linux The default in the distribution Shell Interpreter

1） The following is from Shell Name instead of Bash Shell name ;

2）Bash Shell The essence is a program （ When running , It becomes a process ）

Shell function

（1） Record historical orders （history）

1）“~/.bash_histroy” Record all commands executed by login （ Default 1000 individual ）;

2） The command executed by login is stored in memory , After logging off the system, the memory records it to ~/.bash_history file ;

3） The number of recorded commands can be modified HISTFILESIZE To increase / Reduce

history command ： operation Shell The historical order in the book

Command format 1：histroy n

1）N Is the number , According to recent N Historical orders

2） If there is no N, Then all historical commands are displayed by default

Command format 2：history Options // Operate on historical commands

Options	meaning
-c	Will the current Shell All in history Content removal
-a	Will add history Cache is written to ~/.bash_history In file
-r	take ~/.bash_history The contents of the document read history In cache
-w	The current history Cache is written to ~/.bash_history In file

! command ： Carry out section N History commands

Command format ：!N

//!! Is to execute the last command

（2） command / File completion function （Tab）

1） Command only / Prefix of file name , adopt Tab Key can automatically complete ;

2） If there are multiple commands / The prefix of the file name is the same , Then list all specific names

（3） Command alias settings （alias）

1） To configure “~/.bashrc” File implementation command alias

alias command ： Set alias command （ Temporary settings ）

Command format ：alias The alias command =‘ command Options ’

1） Direct input alias Then all alias commands are displayed

unalias command ： Cancel command alias

Command format ：unalias The alias command

（4） Programming script （shell scripts）

（5） task management 、 The front desk 、 Backstage control （job control、foreground、background）

（6） wildcard （Wilecard）

Father / Son Shell

Father Shell： Sign in CLI or GUI When running the terminal emulator in , Interaction started by default Shell

Son Shell： In the father Shell Under the environment of , New created by invoking the command Shell Program

1） Son Shell Only the father can inherit Shell The global environment variable of ;

bash command ： establish / Callers Shell

Command format ：bash Options

Options	meaning
-c command	Callers Shell After executing the specified command , And return to the parent Shell
-i	Create a child Shell, And enter the sub Shell
-l	With login shell Form creation sub Shell, And enter the sub Shell
-r	Create a child Shell, And enter the sub Shell Dan Zi Shell Cannot switch directories

exit command ： sign out Shell

Command format ：exit

1） if Shell Itself is a child Shell, Will return to the relative child Shell The father of Shell;

2） if Shell Itself is the highest level Shell, It will close Shell;

Such as ： Callers Shell Execute the specified command

Such as ： Create a child Shell, And enter the sub Shell Then return to the father Shell

Such as ： Create restricted child Shell

Built in command

External command （ File system commands ）：Bash Shell Outside the program

1） Usually located in /bin、/usr/bin、/sbin or /usr/sbin in ;

3） Call external command , You need to specify the absolute path of the external command ;

2） When invoking an external command , By default, create a child Shell Run external commands ;

which command ： Query the full path of the command according to the command name

Command format ：which Options Command name

Options	meaning
-a	Put all PATH The commands found in the directory are listed
-v	Display the version information of the command

1） The essence is based on environmental variables （PATH） The path specified , Go to query the file name

2） There are no options , The first full path found is displayed by default

Such as ： Inquire about ls The full path of the command

Internal key command ：Bash Shell Component part （ Compile into one ）

1） The internal key command defaults to the parent Shell Run in ;

type command ： Query whether the command is Bash shell Built in commands

Command format ：type Options Command name

Options	meaning
-a	take PATH In the path of variable definition All file paths containing the command name are listed （ Include alias）
-p	The command is an external command , Will display the full file path If it were not for external orders , Then no data is displayed
-t	Command attributes are represented by special fields

1）type Commands are similar in nature which command ： Find the execution file

2） The special field is ：file（ External command ）、alias（ Command alias ）、builtin（ Internal key command ）

Common internal key commands are as follows ：

command	function
:	Extended parameter list , Perform the redirection operation
.	Read and execute the command in the specified file
alias	Specify the command definition alias
bg	Run the task in background mode
bind	Bind the keyboard sequence to a readline Function or macro
break	Exit loop
builtin	Execute specified Shell Built in command
caller	Returns the context of the active subfunction call
cd	Toggle directory
command	Execute the specified command , Don't make Shell lookup
compgen	Specify word generation possible completion matches
complete	Display the specified word completion process
compopt	Modify the completion options for the specified word
continue	Skip this cycle , So let's do the next loop
declare	Declare variables or variable types
dirs	List the current storage directory
disown	Delete the task specified in the task column
echo	Output the specified text to stdout
enable	Enable / Disable the specified built-in command
eval	Splice the specified parameters into one command , And implement
exec	Specify command substitution Shell process
exit	mandatory Shell Exit with the specified exit status code
export	Specify the variable as the environment variable
fc	Select a command from the history
fg	Transfer the task to the foreground to run
getopts	Analyze the specified positional parameters
hash	Query and record the full pathname of the specified command
help	List the help documents
history	Display the history of the command
jobs	Make a list of tasks
kill	To specify the PID The process signals
let	Calculates each parameter in a mathematical expression
local	Create a variable with limited scope in the function
logout	sign out Shell
mapfile	from stdin Read data row , And join the index data group
popd	Delete record from directory stack
printf	Displays text using a formatted string
pushd	Add a directory to the directory stack
pwd	Displays the path of the current working directory
read	from stdin Read a row of data , And assign it to the specified variable
readarray	from stdin Read data row , And put it into the index data group
readonly	from stdin Read a row of data , And assign it to a read-only variable
return	Force the function to exit with the specified value
set	Sets and displays the values and values of environment variables Shell attribute
shift	Move the position parameters in turn
shopt	open / Close control Shell Variable value for optional behavior
source	Read and execute the command in the specified file
suspend	Pause Shell Implementation , Until receipt SIGCONT The signal
test	Returns the exit status code based on the specified condition 0 or 1
times	Displays the accumulated user and system time
trap	If the specified system signal is received , Then execute the specified command
type	Detect whether it is a built-in command
typeset	Declare variables or variable types
ulimit	Set the specified resource limit for system users
umask	Specify the default mask for document permissions
unalias	Delete the specified alias
unset	Delete the specified environment variable or Shell attribute
wait	Wait for the specified process to complete , And return the exit status code