Passing a variable to a child shell | LPIC-1 101-500 Exam original practice question

103.1Basic

The following two lines were run in the current Bash, and the result was <>.

Without changing LAB_COLOR, make the second command print <blue> when it is run again.

LAB_COLOR=blue
bash -c 'printf "<%s>\n" "$LAB_COLOR"'

Which command should be added between the two lines?

Hint 1: Identify which process needs the value

The second line starts a new Bash process. Separate a variable visible in the current shell from a name-value pair included in the environment inherited by that new process.

Hint 2: Shell state and inheritance

Review the scope of a variable, an exported environment entry, and positional parameters.

Shell variable: A named value held by the current shell; assignment alone does not newly mark it for export.
Environment: Name-value pairs supplied to a process when it is started.
Export attribute: A variable attribute that includes its name and value in environments passed to subsequently executed commands.
Positional parameter: An argument stored as $1, $2, and so on, separate from a named variable such as LAB_COLOR.
Single quotes: Shell quoting that preserves the enclosed characters literally until they are passed to the invoked command.

Detailed explanation

Correctexport LAB_COLOR

Correct. export marks the existing shell variable for inclusion in the environment of child processes.

LAB_COLOR already holds blue. Adding the export attribute keeps that value and makes it available in the environment of a Bash started afterward. It does not retroactively modify a child that is already running.

Incorrectset LAB_COLOR

Incorrect. This sets positional parameters; it does not give LAB_COLOR the export attribute.

With LAB_COLOR as an argument and no option, set replaces positional parameters: $1 becomes the literal text LAB_COLOR. This does not add the export attribute to the named variable. In the stated shell, the value remains blue but the newly started child still lacks it.

Incorrectecho "$LAB_COLOR"

Incorrect. echo only prints the value in the current shell and does not change the child environment.

The current shell expands the value before echo prints it. Seeing blue in that output demonstrates visibility in the parent, but printing a value does not modify the environment passed to another process.

Incorrectunset LAB_COLOR

Incorrect. unset removes the variable, so neither the current shell nor a child shell can read it.

Removing LAB_COLOR leaves no named value to pass to the next child. The later child therefore still prints an empty value instead of the required blue.

Try it yourself

An example you can run in a temporary verification environment.

unset LAB_COLOR
LAB_COLOR=blue
bash -c 'printf "before=<%s>\n" "$LAB_COLOR"'
export LAB_COLOR
bash -c 'printf "after=<%s>\n" "$LAB_COLOR"'

Official references

Expected result

before=<>
after=<blue>

Key points

The difference between shell and environment variables
Inheritance by child processes
When expansion occurs inside single quotes

Notes

Environment: Bash. Use a fresh Bash process so changes to variables and positional parameters do not affect your working shell.
Run the supplied verification sequence in a fresh Bash process: it removes only the task variable there and should print before=<> followed by after=<blue>.
The initial empty result is part of the premise. An assignment to a variable that was already exported can retain its export attribute; do not assume every assignment creates a non-exported variable.

Foundation review

Assignment and export are separate

In this scenario, the observed empty child output establishes that LAB_COLOR is not inherited. Assigning blue stores a shell value; adding the export attribute changes which named values later commands inherit.

Choose the expansion time

The single quotes around the bash -c program stop the outer shell from expanding $LAB_COLOR. The child Bash parses that program and expands the variable using its own environment.

Inheritance starts with the child

A child receives its environment when it starts. Subsequent changes in the child normally do not change the parent shell, and exporting in the parent affects commands started afterward.

Question IDKP-103-001

EnvironmentBash. Use a fresh Bash process so changes to variables and positional parameters do not affect your working shell.

Last technical review2026-10-30

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