Shell – How to restore the changes to shell variable

The processes are organized as a tree: every process has a unique parent, apart from init which PID is always 1 and has no parent.

The creation of a new process goes generally through a pair of fork/execv system calls, where the environment of the child process is a copy of the parent process.

To put a variable in the environment from the shell you have to export that variable, so that it is visible recursively to all children. But be aware that if a child change the value of a variable, the changed value is only visible to it and all processes created after that change (being a copy, as previously said).

Take also into account that a child process could change its environment, for example could reset it to default values, as is probably done from login for example.

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).