A script contains the line `mkdir /srv/data && cp report.txt /srv/data/`. Under what condition does the cp run?
LPIC-1 Exam 102-500, objective 105. Shells and shell scripting medium
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The options
Not correct Always, because && only separates commands on one line.
Wrong. The plain separator that always runs the next command is `;`. `&&` adds a condition.
Not correct Only if mkdir writes nothing to standard output.
Wrong. Output on stdout or stderr is irrelevant to && and ||. Only the numeric exit status is examined.
Correct Only if mkdir exits with status 0.
Correct. `A && B` runs B only when A succeeded. Here that avoids copying into a directory that could not be created.
Not correct Only if mkdir exits with a non-zero status.
Wrong, that is `||`. `A || B` runs B only when A failed, which is the idiom behind `command || exit 1`.
Why
&& and || are short-circuit list operators driven purely by exit status: && runs the right-hand side on success (status 0), || runs it on failure (non-zero). They chain left to right with equal precedence, so `A || B && C` is read as `(A || B) && C`, not as an if/else.
Where this comes from
- Cited
- LPI exam objective 105.2
- What it says
- Use conditional execution based on the exit status of a command.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 105 and space the ones you get wrong.