bash短路一线分配

Question

Can I assign a variable in a short circuit expression in bash?

x=''
y='aaa'
( [ ! -z "$x"  ]  && (echo "using SGE ID" >&2;  num="$x") ) ||  ( [ ! -z "$y" ] && (num="z$y" && echo "trying y" ) )
echo "num : $num : $y"
exit 0

returns:

trying y
num :  : aaa

Seemingly the point of assignment is reached, but it is not evaluated, or is it in a wrong scope?

Answer 1

You can, but parentheses are not for grouping in the traditional sense. The commands inside parentheses run in a subshell, and any variable assignments in a subshell are local to that shell, invisible outside it.

Use braces instead; note that you need a semicolon to terminate the command before a closing brace if it appears on the same line.

x=''
y='aaa'
{ [ ! -z "$x"  ]  && { echo "using SGE ID" >&2;  num="$x"; }; } ||
  { [ ! -z "$y" ] && { num="z$y" && echo "trying y"; }; }
echo "num : $num : $y"
exit 0