Command grouping (&&, ||, …)

Question

We are currently in the /home/student/ directory. We execute the following commands:

pwd; (ls) || { cd .. && ls student/; }  && cd student ||         


        

Answer 1

(ls) is executed in a subshell, because the commands are seperated with ";"

ls is executed in a subshell because of the parentheses. Parentheses introduce subshells.

But I have no idea why other commands are executed?

Unlike other programming languages you might be familiar with, bash does not give && higher precedence than ||. They have equal precedence and are evaluated from left to right.

If you had a || b && c, in other languages this would be read as a || {b && c;}. If a were true then neither b nor c would be evaluated.

In bash, though, it's parsed as {a || b;} && c (strict left-to-right precedence), so when a is true b is skipped but c is still evaluated.