多个值时 if [ -z 报错 binary operator expected

if [ ! -z "\$client_pid" ]; then

报错: line 23: [: 662: binary operator expected

改成

if [[ ! -z "\$client_pid" ]]; then

即可。

unix - binary operator expected error when checking if a file with full pathname exists - Stack Overflow

bash - ERROR: binary operator expected - ZhangZhihuiAAA - 博客园 (cnblogs.com)