環境變數 env

1. Linux 是一個多人多功的系統，每個用戶登入時讀取設定檔 /etc/bashrc 及 /etc/profile 取得工作的環境變數，登入後執行 env 可以列出環境變數。

   [dywang@dywmac ~]$ env
   ORBIT_SOCKETDIR=/tmp/orbit-dywang
   HOSTNAME=dywmac
   IMSETTINGS_INTEGRATE_DESKTOP=yes
   TERM=xterm
   SHELL=/bin/bash
   HISTSIZE=1000
   XDG_SESSION_COOKIE=ac14e52ecfb2492f78ca6a6900000012-1552852991.392630-81397834
   GTK_RC_FILES=/etc/gtk/gtkrc:/home/dywang/.gtkrc-1.2-gnome2
   WINDOWID=69206020
   QTDIR=/usr/lib64/qt-3.3
   QTINC=/usr/lib64/qt-3.3/include
   IMSETTINGS_MODULE=gcin
   USER=dywang
   LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;....
   GNOME_KEYRING_SOCKET=/tmp/keyring-8bgO8w/socket
   SSH_AUTH_SOCK=/tmp/keyring-8bgO8w/socket.ssh
   USERNAME=dywang
   SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/3513,unix/unix:/tmp/.ICE-unix/3513
   PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin
   MAIL=/var/spool/mail/dywang
   DESKTOP_SESSION=gnome
   QT_IM_MODULE=gcin
   PWD=/home/dywang
   XMODIFIERS=@im=gcin
   GDM_KEYBOARD_LAYOUT=us
   GNOME_KEYRING_PID=3503
   LANG=en_US.UTF-8
   GDM_LANG=en_US.UTF-8
   GDMSESSION=gnome
   SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass
   HISTCONTROL=ignoredups
   HOME=/home/dywang
   SHLVL=2
   GNOME_DESKTOP_SESSION_ID=this-is-deprecated
   LOGNAME=dywang
   QTLIB=/usr/lib64/qt-3.3/lib
   CVS_RSH=ssh
   DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-CSMOPauJQO,guid=51ed8f7a36376c036368676d0000002e
   LESSOPEN=||/usr/bin/lesspipe.sh %s
   WINDOWPATH=1
   DISPLAY=:0.0
   G_BROKEN_FILENAMES=1
   COLORTERM=gnome-terminal
   XAUTHORITY=/var/run/gdm/auth-for-dywang-xnorl4/database
   _=/usr/bin/env
   

2. 除了系統預設的環境變數，用戶也可以在自己的家目錄中 .bashrc 及 .bash_profile 設定專屬的環境變數。 變數設定在 /etc/bashrc 或 /etc/profile 兩個檔案 ssh 登入都會生效，但圖形界面開啟 gnome-terminal 不會讀取 /etc/profile，同樣的狀況，用戶設定在家目錄中的 .bashrc 或 .bash_profile ，ssh 登入都生效，但 gnome-terminal 不會讀取 .bash_profile。

   [dywang@dywmac ~]$ vim .bashrc 
   [dywang@dywmac ~]$ tail -1 .bashrc
   myname=dywang
   [dywang@dywmac ~]$ vim .bash_profile 
   [dywang@dywmac ~]$ tail -1 .bash_profile 
   doc=Documents
   [dywang@dywmac ~]$ bash
   [dywang@dywmac ~]$ echo $myname
   dywang
   [dywang@dywmac ~]$ echo $doc
   
   [dywang@dywmac ~]$ exit
   exit
   [dywang@dywmac ~]$ ssh localhost
   Last login: Mon Mar 18 04:56:47 2019 from localhost
   [dywang@dywmac ~]$ echo $myname
   dywang
   [dywang@dywmac ~]$ echo $doc
   Documents