How do I unset a variable at the command line?

To remove an environment variable, run

unset ALL_PROXY

Note that an environment variable only takes effect in a program and the program it launches. If you set an environment variable in one shell window, it doesn't affect other shell windows.

If you've added export ALL_PROXY=… to an initialization file, remove it from there.

You can run export with no arguments to see what environment variables are set in the current shell.

Remember that to make a shell variable available to the programs started by that shell, you need to export it, either by running export VAR after the assignment VAR=VALUE or by combining the two (export VAR=VALUE).

To unset a bound variable in bash use unset VARIABLE (unset ALL_PROXY in your case). This command actually deletes the variable. You can also set the value of a variable to empty by

VARIABLE=

or

VARIABLE=""

The difference is that the two latter commands don't delete the variable. You can see the difference by using the -u flag with set to force it to treat the unset variables as an error while substituting:

/home/user1> var=""
/home/user1> echo $var

/home/user1> set -u
/home/user1> echo $var

/home/user1> unset var
/home/user1> echo $var
-bash: var: unbound variable

In the above example, bash complains about var is unbound (after unsetting its value) which is the expected error (note that this does not happen in second echo command, meaning that var has a value which is empty or null).