In Linux shells like Bash, assigning a variable with VAR=value creates a shell variable, which is only available within the current shell session. To make the variable accessible to child processes (subsequently executed commands), it must be converted into an environment variable. The export command is used for this purpose. It marks the specified variable for export to the environment of child processes. The syntax export ENABLEAUTH=1 both declares the variable and exports it in a single step, fulfilling the requirement.

A. let is a shell builtin used for evaluating arithmetic expressions, not for setting environment variables.

B. This command creates a local shell variable, which is not inherited by child processes or sub-shells.

C. This command substitution reassigns the variable's existing value to itself; it does not export it.

1. GNU Bash Reference Manual. (2022). 4.2 Bash Builtin Commands. "The export builtin command marks the names of shell variables to be passed to child processes in the environment." Retrieved from https://www.gnu.org/software/bash/manual/bash.html#index-export

2. Sobell

M. G. (2018). A Practical Guide to Linux Commands

Editors

and Shell Programming. Pearson Education. Chapter 8

"The Bourne Again Shell

" section on "User-Created Variables

" explains the difference between local and environment variables and the use of export.

3. University of Cambridge

Computing Service. (n.d.). Introduction to the Unix shell for data processing. Section "Variables". "To make a variable available to other programs we run from the shell

we must export it."