如何首先扩展字符串然后求值？

Question

非常简单：如何进行这项工作：

export predicate='[[ $LINE $arg ]]'
export LINE=10
export arg='-gt 3'
eval $predicate

产生：

eval "${predicate}"
bash: conditional binary operator expected
bash: syntax error near `$arg'
bash -x -c 'eval "${predicate}"'

尝试2：

$ eval $(echo ${predicate})
bash: conditional binary operator expected
bash: syntax error near `$arg'

尝试3：

+ eval '[[ $LINE $arg ]]'
bash: eval: line 0: conditional binary operator expected
bash: eval: line 0: syntax error near `$arg'
bash: eval: line 0: `[[ $LINE $arg ]]'

根本就没有扩展这些变量。