The export command is a Bash built-in command that exports environment variables and functions for use in other shell sessions1. Environment variables are named values that affect the behavior of applications and processes2. For example, the PATH variable stores a list of directories where executable programs are located, and the LANG variable sets the language and locale of the system2. By using the export command, you can make these variables available to any child process spawned by the current shell1. For example, if you want to set the EDITOR variable to vim for all subshells, you can run:

export EDITOR=vim

The export command can also be used to export functions, which are blocks of code that can be reused by invoking their name3. For example, if you want to create and export a function that prints “Hello world”, you can run:

hello () { echo “Hello world”; } export -f hello

Then, you can call the hello function in any subshell or script that inherits the environment from the current shell.

The other options are not related to the export command. Option A refers to the mount command, which attaches a filesystem to a directory4. Option B refers to the command substitution feature, which runs a command in a subshell and replaces it with its output5. Option C refers to the history command, which displays the command history of the current shell. Option E refers to the exportfs command, which maintains the table of exported NFS shares.