Linux Common commands

Type of command:

Internal command: Command that comes with the shell program

External command: itself is an independent executable program

How to distinguish internal commands from external commands: Using the "type command"

PRINTENV Display Environment variables

Hash Display cache

Help Hash

Hash-r Clearing Cached content

Logout Log out session

Whatis "Commands" To view the man chapter

External Command lookup: $PATH

The first runtime is found in $path, and the lookup results are cached

Bash Key Features

echo $HISTCONTROL History command display settings

Histcontrol can be assigned a value

Ignoredups: Ignoring duplicate commands, successive identical commands will be considered duplicates

Ignorespace: Ignore commands that start with whitespace characters

Ignoreboth: Both of these ignore

Date Command common options

+%F: Format with%y-%m-%d

+%d: Format with%m/%d/%y

+%t: Time, format with%h:%m:%s

+%y: Year

+%m: Month

+%d: Date (01-31)

+%h: Hours (00-23)

+%i: Hours (01-12)

+%m: minutes (00-59)

+%s: Seconds (00-60)

+%s: Timestamp timing, the number of seconds elapsed from the beginning of Unix (1970-01-01-00:00:00) to this moment.

+%u: Show weeks

Linux has two clocks: system clock and hardware clock

Hwclock display hardware clock

Date display system clock

Hwclock-s the hardware clock is the standard

-W with system clock

Which display the full path of the command

which--skip-alias ls skip command alias

Stat Display file meta data

Stat/root/.bash_history

Changes in file content influence Modify-time Mtime

File meta-data changes affect Change-time CTime

Touch Changes Atime and Mtime

Touch-a Change only Atime

-M only changes Mtime

Cat command: Connect and display file contents

Cat/etc/{issue,fstab}

CAT-E Display newline characters

Text file: Is data stream (stream)

Echo-n does not end with a newline character

Echo-e echo-e ' Hello \ n World ' makes escape character

\ t \ n Common

Display color \033[single digit: controls the font itself

3#: #是一个数字, 3 means control foreground color

4#: #是一个数字, 4 for controlling background color

Combined use

Echo-e ' \033[33mhello\033[0m '

M: Fixed format

\033[0m: The control function ends, and if there is no control flag, the CAP font does not revert to color.

Cp-p preserving file meta data

Sort:-F ignores character case

-T Specify delimiter

-k Specifies the sort field

-N Sort by numeric value

-U Go Heavy

Uniq: Go to the heavy command

-D Show only duplicate rows

-U displays only non-repeating rows

-C shows the number of repetitions per line

Bash features input, output rewrite direction, and piping

Set-c Turn off the overwrite function of output redirection

>|: Overwrite operation is still performed when output redirection override is turned off

&>: Correct, error output to the same file

<: Input redirection

<<:here Document

Cat <<end: End after input end

Cat >>/tmp/myfile <<eof

/etc/shells Directory

Users cannot log on to the system if the user is using a default shell that is not in this directory

md5sum file name

MD5: fixed length output 128bits

Sha512sum file name

SHA1: fixed length output 160bits

Encrypt password

OpenSSL passwd-1-salt 12345678

User Management

/etc/shadow format

User name: encrypted password: Last password change time (days): Minimum password Age: Password maximum age: Password Expiration warning interval: Inactivity period: Account expiration: Reserved area

Usermod-g modify additional groups by appending it with the "-a" option

Usermod-d modifies the location of the home directory with the "-m" option to ensure that the home directory is created and that the user's original files are moved to the new home directory.

USERMOD-L User name: Modify user Name

Chsh USERNAME Change Shell

CHFN USERNAME Change Annotation information

Id:

ID-G user1 display Group ID

ID-GN User1 Display Group name

Id-u user1 display User ID

Determine if a user exists

ID User1 &>/dev/null

echo $?

Su:switch User

Su-l = Su-

Su-c ' COMMAND '

Temporarily switch basic groups

Log on to the user who wants to switch groups, NEWGREP group name

Bash's configuration file

Global configuration

/etc/profile,/etc/profile.d/*.sh,/etc/bashrc

Personal configuration

~/.bash_profile,~/.bashrc

File for Profile class:

Setting environment variables

Run a command or script

BASHRC class file

Setting Local Variables

Defining command aliases

How the login shell reads the configuration file

/etc/profiel-/etc/profiel.d/*.sh-~/.bash_profile-~/.bashrc-/etc/bashrc

Non-sign-on shell

~/.bashrc-/etc/bashrc-/etc/profile.d/*.sh

Linux Common commands