判断语句

liucody

(( 0 && 1 ))
echo $? # 1 ***   为什么是 1？
# And so ...
let "num = (( 0 && 1 ))"  
echo $num # 0    为什么是0
# But ...
let "num = (( 0 && 1 ))"
echo $? # 1 ***     为什么嘛

tc1989tc

please man bash. then search \(\( and let:

man bash.

((expression))
              The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the
              value of the expression is non-zero, the return status is 0; otherwise the return status is 1.  This is
              exactly equivalent to let "expression".

let arg [arg ...]
              Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION above).   If  the  last
              arg evaluates to 0, let returns 1; 0 is returned otherwise.

?      Expands to the exit status of the most recently executed foreground pipeline.