Special Shell variables
1. Environment variables:
An environment variable is a class of variables that the system itself needs to be created in advance by the LIUNX system.
Mainly used for the user's working environment, including (user's host directory, command lookup path, user's current directory, landing terminal, etc.) the value of the environment variable is maintained by the operating system itself, and changes with the user's state.
Env Tune Current environment variable
[[Email protected] ~]# env
xdg_session_id=2
Hostname=xlous.com
Selinux_role_requested=
Term=linux
Shell=/bin/bash
histsize=1000
ssh_client=192.168.1.116 51516 22
Selinux_use_current_range=
Ssh_tty=/dev/pts/1
User=root
ls_colors=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=01;05 ; 37;41:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*. arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*. t7z=01;31:*.zip=01;31:*.z=01;31:*. Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31 :*. tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:* . alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*. gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*. tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:* . m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01; 35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:* . anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.mid=01;36:*.midi=01;36:*.mka=01;36:*. MP3=01;36:*.MPC=01;36:*.OGG=01;36:*.RA=01;36:*.WAV=01;36:*.AXA=01;36:*.OGA=01;36:*.SPX=01;36:*.XSPF=01;36:
Mail=/var/spool/mail/root
Path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
Pwd=/root
Lang=zh_cn. UTF-8
Selinux_level_requested=
Histcontrol=ignoredups
Shlvl=1
Home=/root
Logname=root
ssh_connection=192.168.1.116 51516 192.168.1.175 22
lessopen=| | /usr/bin/lesspipe.sh%s
xdg_runtime_dir=/run/user/0
display=localhost:10.0
_=/usr/bin/env
The PWD command calls this variable in order to output.
$PWD
[Email protected] etc]# echo $PWD
/etc
[[Email protected] etc]# CD
[Email protected] ~]# pwd
/root
$PATH Define the default search path for a command
[Email protected] ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
Note: Only commands executed by yourself can be used directly in the directory included in the path variable, and tab completion is used. If you are not under the path included in path, you can only use absolute or relative paths.
[Email protected] ~]# echo $USER
Root
[Email protected] ~]# echo $SHELL
/bin/bash
[Email protected] ~]# echo $HOME
/root
[Email protected] ~]# echo $LANG
Zh_cn. UTF-8
Linux commands 16