How do I delete an exported environment variable?
 Before installing gnuplot, I set the environment variable GNUPLOT_DRIVER_DIR = /home/gnuplot/build/src .  During the installation, something went wrong.  
 I want to remove the GNUPLOT_DRIVER_DIR environment variable.  How can I achieve it?  
 unset是您正在查找的命令。 
unset GNUPLOT_DRIVER_DIR
Walkthrough of creating and deleting an environment variable in bash:
Test if the DUALCASE variable exists:
el@apollo:~$ env | grep DUALCASE
el@apollo:~$ 
It does not, so create the variable and export it:
el@apollo:~$ DUALCASE=1
el@apollo:~$ export DUALCASE
Check if it is there:
el@apollo:~$ env | grep DUALCASE
DUALCASE=1
It is there. So get rid of it:
el@apollo:~$ unset DUALCASE
Check if it's still there:
el@apollo:~$ env | grep DUALCASE
el@apollo:~$ 
The DUALCASE exported environment variable is deleted.
Extra commands to help clear your local and environment variables:
Unset all local variables back to default on login:
el@apollo:~$ CAN="chuck norris"
el@apollo:~$ set | grep CAN
CAN='chuck norris'
el@apollo:~$ env | grep CAN
el@apollo:~$
el@apollo:~$ exec bash
el@apollo:~$ set | grep CAN
el@apollo:~$ env | grep CAN
el@apollo:~$
 exec bash command cleared all the local variables but not environment variables.  
Unset all environment variables back to default on login:
el@apollo:~$ export DOGE="so wow"
el@apollo:~$ env | grep DOGE
DOGE=so wow
el@apollo:~$ env -i bash
el@apollo:~$ env | grep DOGE
el@apollo:~$
 env -i bash command cleared all the environment variables to default on login.  
这也可能起作用。
export GNUPLOT_DRIVER_DIR=
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