Linux Learning Notes (23)

First, Shell Foundation

The shell is a command interpreter that provides interaction between the user and the machine

Each user can have their own specific shell

Centos7 default shell is bash (Bourne Agin Shell)

Besides bash, there's zsh.ksh and so on.

Ii. History of the Order

The commands that have been knocked are stored in the/root/.bash_history and can store up to 1000 records.

You can use the history command to view

History-c can erase the history of the command in memory, but cannot clear the command in the config file/root/.bash_history

Echo $HISTSIZE look at the environment variables to see how many commands can be stored.

/etc/profile inside can change the environment variable

Source/etc/profile Refresh profile to make environment variables effective immediately

histtimeformat= "%y%m%d%h:%m:%s" allows history to temporarily display the input time of the historical command

If you want to be effective, add histtimeformat= "%y%m%d%h:%m:%s" line to/etc/profile

Source/etc/profile Refresh a profile file to

Permanently save/root/.bash_history don't want to be destroyed or deleted by others

Chattr + a/root/.bash_history Add a permission to this user

If you do not exit normally, use Exit or logout. Then the history command is not preserved.

！！ Execute the last command

！ n N represents a number. Which history command to execute

！ command executes the specified command for the last input

Third, command completion is the alias

tab, if there is only one start, click Auto-Complete. If it is more than two, press two to complete the auto-completion

Yum install-y bash-completion Download a package with auto-completion parameters (need to be active from new boot)

Alisa Aliases

Alisa View all Alisa commands in the system

alisa+ alias = ' command ' create Alisa Alias

unalisa+ aliases Cancel the Alisa alias you created

Four, wildcard characters

* No characters or numbers

？ An arbitrary character.

[] inside can write a range. For example, 0-3 or 123, 13 displays 1 and 3 only.

{} is equivalent to 13 square brackets, but the middle is added,

V. Input/Output redirection

> direct the output of the preceding command directly to the following file, overwriting the original contents of the following file

Cat 1.txt > 2.txt

>> append the output of the preceding command to a later file

Cat 1.txt >> 2.txt

2> Error Redirection

2>> Error Append redirect

&> = > and 2>

&>> = >> and 2>>

When you write a shell script, you can separate the errors and correct them to check the script

Linux Learning Notes (23)