An executable script contains only the line `export EDITOR=vim`. After running it as `./setenv.sh`, `echo $EDITOR` in the calling shell prints nothing. What explains this?
LPIC-1 Exam 102-500, objective 105. Shells and shell scripting medium
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The options
Not correct The script is missing execute permission, so the assignment never ran.
Wrong. Without execute permission the shell would refuse to run it and print a permission-denied error, not run it silently.
Not correct export only works for variables that already exist in the environment.
Wrong. `export NAME=value` creates the variable and marks it for export in one step. Existence beforehand is not required.
Not correct Environment variables must be assigned with set instead of export.
Wrong. `set` is a real builtin, but it toggles shell options and sets positional parameters. It does not create environment variables.
Correct Executing the script starts a child shell, and a child can never alter its parent's environment.
Correct. Exported variables propagate downward to children only. To change the current shell you must run the script with `source setenv.sh` or `. setenv.sh`, which executes its lines in the current shell.
Why
Executing a script forks a new process running a new shell. Anything that shell changes, including variables, the working directory and umask, dies with it. Sourcing (`.` or `source`) does not fork: the commands run in the current shell, so their side effects persist. This is exactly why ~/.bashrc is sourced rather than executed.
Where this comes from
- Cited
- LPI exam objective 105.1
- What it says
- Understand the difference between sourcing a file and executing it.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 105 and space the ones you get wrong.