What is the command to modify environment variables in Linux?

The command used to modify environment variables in Linux is "export." This command is essential for modifying the environment variables for the current shell session or for making them available to child processes that may be spawned by that shell. When you use "export" followed by the variable name and value, it ensures that the variable is added to the environment and is accessible to any subsequent commands executed in that session.

For example, if you want to set the MY_VAR environment variable to "value," you would use the command export MY_VAR=value. After executing this command, MY_VAR would be available in the environment for any processes launched from that terminal.

The other options listed do not represent standard commands for modifying environment variables in a Linux shell. "alterenv" and "setvar" are not recognized Linux commands, and while "setenv" is used in some Unix-like systems (notably in csh and tcsh) for setting environment variables, it is not typically used in the more commonly used bash shell. In bash, "export" is the appropriate command to utilize.