Select the TWO true statements about shell variables and the environment in bash.
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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The options
Choose 2.
Not correct A variable assigned without export is still visible to programs started from that shell.
Wrong. Without export it is a shell variable only, so a program the shell executes — including a script run as ./script.sh — never receives it in its environment. (A forked subshell such as ( ... ) or $( ... ) is a copy of the same shell and does still see it; that is not a new program.)
Correct export VAR marks VAR so that it is placed in the environment of commands the shell starts.
Correct. Exported variables are inherited by child processes; that inheritance is the whole point of export.
Not correct set with no arguments prints only the exported variables.
Wrong. `set` with no arguments prints all shell variables AND shell functions. It is `env` (or `export -p`) that shows the exported environment.
Not correct env with no arguments prints every shell variable, exported or not.
Wrong. env prints the environment it received, which contains only exported variables. It is also used to run a command with a modified environment, e.g. env LANG=C sort.
Correct unset VAR removes the variable from the current shell entirely.
Correct. unset deletes the variable (or a function, with -f), which is different from setting it to an empty string.
Why
Bash keeps shell variables and the environment as two overlapping sets. Assignment creates a shell variable; export promotes it into the environment so child processes inherit it; unset removes it. `set` lists shell variables and functions, `env` lists the environment. Remember that changes made in a child can never propagate back to the parent shell — which is why you source a script instead of executing it when you want its variables to stick.
Where this comes from
- Cited
- LPI exam objective 103.1
- What it says
- Shell variables versus environment variables; export, set, unset and env.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 103 and space the ones you get wrong.